木村 真晃

The joint strength and its improvement of AA5083 Al alloy joints fabricated by friction stud welding method were investigated. The diameter of the work and stud side specimens were 32.0 mm and 12.8 mm, respectively, and those were friction welded. The appropriate welding condition for obtaining high tensile strength was established as follows: a friction speed of 17.5 s⁻¹, a friction pressure of 80 MPa, a friction time of 1.6 s, and a forge pressure of 360 MPa. However, all joints fractured between the initial weld interface and the work or stud sides, i.e. the fracture did not occur in the base metal. It could be considered that the initial oxide film on the weld faying surface of the work side was not exhausted as the flash during the welding process. To obtain the joint having the fracture in the base metal, the suitable shape at the weld faying portion of the work side specimen was suggested as the groove shape. The inner diameter of the groove corresponded to the same diameter of the stud side, and that had a groove width of 3.0 mm with a groove depth of 1.0 mm. As a conclusion, AA5083 friction stud welded joint, which had the tensile strength of the base metal and the fracture in the base metal, could make with the appropriate welding condition. Furthermore, the weld faying portion at the work side should be in the suitable shape that urges the extrusion of the flash from this side.

To reduce weigh of the transportation machines, joining of the FRP and the light metal is considered as important technique. In this study, the punching rivet method was applied to make joints between a GFRP sheet and an aluminum alloy A6061 sheet and joint strength was examined. The punching rivet method is possible to join the sheets without drilling by using a rivet and a rivet holder. The punching-out process of the sheets using a rivet shank as a punch and the joining process of the sheets using the rivet and the rivet holder are continuously performed. From the experimental results of joining of the GFRP sheet and the A6061 sheet, the joints made by the punching rivet method had no large crack and out-of-plane deformation of the joints was suppressed. From the results of the joint strength tests, the joints made by the punching rivet method had almost the same joint strength as the bolted joints which were tightened by regulated torque. In addition, the fatigue life of the joints made by the punching rivet method was longer than that of bolted joints. It could be confirmed that the punching rivet method was effective to join the GFRP sheet and the A6061 sheet.

This paper describes the stud shape and joint strength of low carbon steel joints fabricated by friction stud welding with low load force requirement. To reduce the load force during the welding process, the stud side with the circular hole at the weld faying surface part was used. The outer diameter of a cylindrically shaped stud side had 12.0 mm and that was welded to the circular solid bar with a diameter of 24.0 mm as the work side. The joint was made with a friction speed of 27.5 rps, a friction pressure of 60 MPa, and a forge pressure of 60 MPa, which was determined as the low force condition for obtaining good joint in the previous study. When joints were made by a cylindrically shaped stud with a hole diameter of 6.0 mm and its depth of 0.5 mm, all joints at a friction time of 0.6 s, i.e. the friction torque reached to the initial peak, had the same tensile strength as that of the base metal with the base metal fracture. All joints with flash from the initial weld interface had the fracture on the base metal, the bend ductility of over 15° with no cracking at the initial weld interface through an impact shock bending test, and a high fatigue strength of the base metal. That is, the sound joint could be successfully achieved, and that could be obtained with the same friction stud welding condition of the circularly shaped solid stud. As a conclusion, the joining technique for the friction stud welding method with low load force requirement was proposed in accordance with using a cylindrically shaped stud that has the circular hole with the shallow depth at the weld faying surface part.

This paper describes the stud shape and joint strength of low carbon steel joints fabricated by friction stud welding with low load force requirement. To reduce the load force during the welding process, the stud side with the circular hole at the weld faying surface part was used. The outer diameter of a cylindrically shaped stud side had 12.0 mm and that was welded to the circular solid bar with a diameter of 24.0 mm as the work side. The joint was made with a friction speed of 27.5 s^-1, a friction pressure of 60 MPa, and a forge pressure of 60 MPa, which was determined as the low force condition for obtaining good joint in the previous study. When joints were made by a cylindrically shaped stud with a hole diameter of 6.0 mm and its depth of 0.5 mm, all joints at a friction time of 0.6 s, i.e. the friction torque reached to the initial peak, had the same tensile strength as that of the base metal with the base metal fracture. All joints with flash from the initial weld interface had the fracture on the base metal, the bend ductility of over 15 degrees with no cracking at the initial weld interface through an impact shock bending test, and a high fatigue strength of the base metal. That is, the sound joint could be successfully achieved, and that could be obtained with the same friction stud welding condition of the circularly shaped solid stud. As a conclusion, the joining technique for the friction stud welding method with low load force requirement was proposed in accordance with using a cylindrically shaped stud that has the circular hole with the shallow depth at the weld faying surface part.

The microstructure and mechanical properties of the AlSi12CuNi alloy fabricated by the additive manufacturing technique, laser powder bed fusion (L-PBF), were investigated. Several laser irradiation conditions were examined to optimize the manufacturing process to obtain a high volume density of the fabricated alloy. Good fabricated samples with a relative density of 99% or higher were obtained with no cracks. The fabricated samples exhibited significantly good mechanical properties, such as ultimate tensile strength, breaking elongation, and micro-hardness, compared to the conventional die casting AlSi12CuNi alloy. Fine microstructures consisting of the α-Al phase and a nano-sized eutectic Al-Si network were observed. The dimensions of the microstructures were smaller than those of the conventional die-casting AlSi12CuNi alloy. The superior mechanical properties were attributed to the microstructure associated with the rapid solidification in the L-PBF process. Furthermore, the influence of the building direction on the mechanical properties of the fabricated samples was evaluated. The ultimate tensile strength and breaking elongation were significantly affected by the building direction; mechanical properties parallel to the roller moving direction were significantly better than those perpendicular to the roller moving direction. In conclusion, AlSi12CuNi alloys with good characteristics were successfully fabricated by the L-PBF process.

To obtain multimaterial structures composed by various materials as the right man in the right place for improvement of the additional value of some products or parts, the easy manufacturing method of the dissimilar metal joint is necessary. This paper described the weldability and its improvement of the friction welded joint between ductile cast iron (JIS FCD400) and typical Al-Mg alloy (JIS A5052). When both materials welded, only the A5052 side was unilaterally deformed and that was exhausted as flash during the friction process regardless of the friction welding condition. The relatively high tensile strength of the joint was obtained when that was made with a friction speed of 27.5 s⁻¹, a friction pressure of 20 MPa, a friction time of 1.5 s, and a forge pressure of 270 MPa. However, the joint had approximately 77% in the tensile strength of the A5052 base metal and that was fractured at the weld interface. The tensile strength of joints, which were made with other friction welding conditions, was lower than that of this friction welding condition. Although the weld interface of the joint had no intermetallic compound interlayer, the fractured surface at the A5052 side had the C element as the graphite particles that were supplied from the FCD400 side. To improve the joint strength, the graphite particle was reduced from the weld faying surface at the FCD400 side by decarburization treatment before welding. The joints had approximately 97% in the tensile strength of the A5052 base metal, and one of joints was fractured at the A5052 base metal. Thus, the graphite particle at the FCD400 side influenced the weldability between FCD400 and A5052. In conclusion, the joint with high tensile strength as well as the possibility for the improvement of the fractured point of them could be obtained when they were made with an opportune friction welding condition and no graphite particles at the weld faying surface of the FCD400 side.

Mechanical properties of AlSi12 alloy, which was manufactured by laser powder bed fusion (LPBF) technique, were investigated. Some basic properties of fabricated objects such as density and tensile strength were clarified. The suitable laser irradiation condition of fabricated objects that had own high relative density was showed. The microstructure of fabricated objects with as-manufactured condition was also evaluated. The fabricated objects exhibited the similar ultimate tensile strength and the Young’s modulus according to the building directions, although other mechanical properties slightly differed. Mechanical properties of fabricated objects made by reused powders also exhibited the similar values of those manufactured by unused powders. In contrast, the mechanical properties excluding the Young’s modulus of the fabricated objects, which were annealed, differed due to annealing treatment. Furthermore, the mechanical properties excluding the Young’s modulus of the fabricated objects for the designed shapes manufactured to the tensile test specimen were smaller than those of the fabricated objects machined from LPBFed rectangular block. Therefore, the attention is necessary for the mechanical design of fabricated object through LPBF technique and that with annealing treatment, because of the difference in the mechanical properties between the object built as the designed shape and the object made from LPBFed bulk product.

The characteristics of the friction welded joint between Al-Mg-Si alloy (AA6063) and austenitic stainless steel (AISI 304, 304SS) through post-weld heat treatment (PWHT) were investigated. The joints were made with a friction speed of 27.5 s⁻¹, friction pressure of 30 MPa, friction time of 1.5 s, and forge pressures of 30 or 240 MPa. As-welded joints had no intermetallic compound (IMC) interlayer at the weld interface. However, the joint with a forge pressure of 30 MPa was fractured between the weld interface and the AA6063 side, and that of 240 MPa was fractured from the AA6063 side. The tensile strength of joints through PWHT process decreased with increasing heating temperature and its holding time. The fractured portion of joints with a forge pressure of 30 MPa changed to the AA6063 side from between the weld interface and the AA6063 side, but that of joints with 240 MPa were fractured from the AA6063 side. Then, all joints with following PWHT conditions fractured at the weld interface; a heating temperature of 773 K and holding time of 3.6 ks, or those of 798 K and 21.6 ks. The fractured surface of joints through PWHT process had IMC interlayer. PWHT condition could express by the Larson-Miller parameter, and the weld interface fracture could divide with a threshold value of this parameter. In conclusion, the fractured point of the joint between AA6063 and 304SS was influenced by the IMC interlayer at the weld interface that was generated during the PWHT process.

In this study, the microstructure and mechanical properties of AlSi12CuNi alloy fabricated by Selective Laser Melting (SLM) were investigated. Wide range of laser irradiation conditions were selected to optimize the process in terms of optimum volume density. As a result, fabricated objects with a relative density of 99% or higher and no crack could be obtained. The as-fabricated alloy exhibited significantly good mechanical properties; an ultimate tensile strength, a breaking elongation, and micro-hardness in comparison with the conventional die casting AlSi12CuNi alloy. The fine microstructures composed of the α-Al phase and nano-sized eutectic Al-Si network could be observed. The dimensions of the microstructures were smaller than that of the conventional die casting AlSi12CuNi alloy. The superior mechanical properties were attributed to the microstructure associated with the rapid solidification of the SLM process. The influence of building direction of mechanical properties on fabricated objects was evaluated. The ultimate tensile strength and breaking elongation were significantly affected by the building direction, which was higher in the case of a parallel direction to the roller moving direction. AlSi12CuNi alloy with good characteristics can be successfully fabricated by the SLM process.

To obtain dissimilar joint for easily making multimaterial structures, the characteristics of friction welded joint between ductile cast iron (FCD400) and 5052 Al alloy (A5052) was investigated. The relatively high tensile strength of joint was obtained when that was made with a friction speed of 27.5s^-1, a friction pressure of 20MPa, a friction time of 1.5s, and a forge pressure of 270MPa, respectively. However, this joint had approximately 77% in the tensile strength of the A5052 base metal and that was fractured at the weld interface. Although the weld interface had no intermetallic compound layer, the fractured surface at the A5052 side had some graphite particles that were supplied from the FCD400 side. To improve the joint strength, the graphite particles were reduced from the weld faying surface at the FCD400 side by decarburization treatment. The joint had approximately 96% in the tensile strength of the A5052 base metal and that was fractured between the A5052 side and the weld interface. The joint with high tensile strength as well as the possibility improving the fractured point of that were obtained when those were made with opportune friction welding condition and no graphite particles at the weld faying surface of the FCD400 side.

In this study, the effect of core bar inserted into weld faying part to obtain an ideal pipe joint with non-generating inner flash via friction welding is described. A steel pipe with inner and outer diameters corresponding to 8.0 mm and 13.5 mm was used, and the weld faying surface was machined to a groove shape of a flat (butt) type. The core bar of various materials was inserted in the weld faying part of the pipes, and those pipes were welded with a friction speed of 27.5 s⁻¹ and friction pressure of 30 MPa. The core bars did not decrease inner flash when joints were fabricated with a core bar of some metallic materials with melting points below that of steel; thus, they were melted during the welding process. The joint with an alumina core bar did not decrease inner flash and was crushed by generating an inner flash. However, a commercially pure tungsten (CP-W) core bar was successfully achieved for decreasing the inner flash. Additionally, all joints with a CP-W core bar did not exhibit the tensile strength of the base metal and a fracture in the base metal, when they were fabricated during the same time, the friction torque reached the initial peak. The joint exhibited a fracture in the base metal when it was fabricated with a CP-W core bar and a taper groove shape that was proposed in the previous study. Furthermore, the core bars were easily removed from the joints; thus the joint with almost no inner flash was successfully obtained. To reduce the inner flash of pipe joints, they should be fabricated with a CP-W core bar inserted into the weld faying part with a taper groove shape.

This paper reported the effects of tensile strength on friction welding condition and weld faying surface properties of friction welded joints between pure copper (OFC) and austenitic stainless steel (AISI 304). The joining phenomena and the joint tensile strength at various friction welding conditions were investigated. The maximum temperature of the joint at a friction pressure of 90 MPa was lower than that of 30 MPa. Also, the central portion of the weld interface of the joint with high friction pressure was not joined completely. Hence, it was showed that the joint should be made with a low friction pressure. In addition, the friction torque curve, joint appearance, flash quantity, and axial shortening of joints differed by virtue of the polishing timing at the weld faying surface, and they were influenced by the surface condition of the OFC side before welding. As a conclusion, the good joint with the fracture in the OFC side should be made with a low friction pressure such as 30 MPa, a friction time after the friction torque reached the initial peak such as 3.6 s, and a high forge pressure such as 270 MPa. Furthermore, the weld faying surface of the OFC side should be polished just before welding, and it was suggested.

Joint strength of dissimilar thin pipe friction welded joints between 5052 Al alloy (A5052) and 304 stainless steel (SUS304) was investigated. Pipes had the outer diameter of 16 mm and the inner diameter of 12 mm, and those were welded with a friction speed of 27.5 s⁻¹, a friction pressure of 30 MPa, and a friction time of 1.2 s. When joints were made with as-received pipes, the joint strength at a forge pressure of 60 MPa had approximately 64% in the tensile strength of the A5052 base metal although that had scattering. Almost all joints fractured between the weld interface and the A5052 side though some joints fractured in the A5052 side. Thus, the fractured portion of joints had scattering at the same friction welding condition. On the other hand, the joint strength at a forge pressure of 50 MPa had approximately 77% in the tensile strength of the A5052 base metal when joints were made by pipes with the machined of the inner and outer diameter parts from solid bars. In addition, all joints fractured from the A5052 side. That is, to obtain good joint such as the fracture in the A5052 side without scattering of the fractured portion of joints, the joint should be made without the affected layer on the pipe surface at the manufacturing of itself.

Direct friction welding between type 7075-T6 aluminum alloy (AA7075) and low-carbon steel (LCS) is extremely difficult, since AA7075 flash has cracks that reach the weld interface during the welding process. In this study, to obtain a joint with no cracks in the flash, AA7075 and LCS were simultaneously friction welded by using pure Al (CP-Al) as an insert metal. The resulting joint had no cracks in the AA7075 flash. When joints were made at a friction pressure of 36 MPa, the joint strength increased with the applied friction time; a friction time of 6.5 s or longer provided approximately 40% of the tensile strength of the LCS base metal. Moreover, the joint strength for a friction time of 6.5 s increased with increasing forge pressure; a forge pressure of 450 MPa provided approximately 71% of the tensile strength of the base metal. That is, the joint strength was higher than the yield strength of the LCS base metal. This joint did not have any not-joined regions or any intermetallic compound layer at both weld interfaces. These results indicate that a good joint between AA7075 and LCS can be easily made by simultaneous friction welding with CP-Al as an insert metal.

The groove shape of the weld faying part was investigated to obtain an ideal pipe friction-welded joint that had a fracture in the base metal and no inner flash of it. The steel pipe had inner and outer diameters of 8.0 mm and 13.5 mm, respectively, and the weld faying surface was of a basic flat shape (butt) type. Moreover, stepped and tapered groove shapes were prepared. Pipe groove shapes were welded with a friction speed of 27.5 s⁻¹ and a friction load of 2.79 kN. Joining phenomena during the welding process were observed, and the tensile strength of joints was evaluated. The joints, that fabricated with flat or step groove shapes, made with a friction time at which the friction torque reached the initial peak did not have the tensile strength of the base metal nor a fracture in the base metal. However, the joints fabricated with a friction time that reached past the initial peak had a large flash, and they contained a fracture in the base metal. In contrast, when joints were made with a gently tapered groove shape with a friction time reaching the time of the initial peak, they achieved a fracture in the base metal, despite having an extremely small inner flash. Therefore, the shape at the weld faying part was capable of reducing the flash exhausted from the weld interface.

In order to obtain easily good joint with no crack at the interface between Ni-based superalloy (Ni-SA) and heat-resistant steel (HRS), the investigation of weldability in those material combinations by friction welding method is required. This paper described the joining phenomena and the tensile strength of the friction-welded joint between Ni-SA and HRS. The joining phenomena during the friction process, such as joining behaviour and friction torque, were measured. The effects of friction pressure, friction time, and forge pressure on the joint tensile strength were also investigated, and the characteristics of joints were observed and analysed. The good joint, which had the fracture in the HRS base metal and the tensile strength of its base metal with no crack at the weld interface, could be successfully achieved, although it had the hardened and softened areas at the adjacent region of the weld interface. In conclusion, it was found that the joint should be made with an opportune friction time after the HRS side was transferred to the entire weld interface on the Ni-SA side and with adding high forge pressure such as 360 MPa. Hence, the good joint could be obtained by friction welding method.

This paper describes the effects of natural aging and heat treatments conditions on mechanical properties of dissimilar composite between 6061 Al alloy (AA6061) and Al-Si12CuNi (AC8A) Al cast alloy, which was fabricated by friction welding. The dissimilar composite was composed of specimens with the pipe part which had an outer diameter of 30.0 mm and an inner diameter of 24.0 mm. This composite had the softened region at the adjacent region of the interface of both materials. The softened region of both sides of the composite recovered the hardness with increasing natural aging time, and those with a natural aging time of 35 days (1 month) or longer had almost similar softened region. Then, the composite with a natural aging time of 35 days (AW composite) had approximately 62% in the tensile strength of the AC8A base metal. The fractured point was the adjacent region of the interface at the AC8A side, i.e. the softened region. The softened region of AW composites, which were re-treated with T6 condition of each base metal, was also recovered. Those composites had approximately 58% in the tensile strength of the AC8A base metal, and those fractured from the corner part of the inner diameter in the AC8A side. In addition, the composite with the high temperature environment with a heating temperature of 473 K, which was re-treated with T6 condition of the AC8A base metal, fractured from the corner part of the inner diameter in the AC8A side. That is, the interface of the composite tightly joined. The possibility that can use the composite fabricated by friction welding as an engine piston was obtained by experimental approach, because the composite did not have the fracture from the interface.

This study focuses on the opening mode of induction bends thismode represents the deformation outside a bend. Bending experiments on induction bends are shown and the manner of failure of these bends was investigated. Ruptures occur at the intrados of the bends, which undergo tensile stress, and accompany the local reduction in wall thickness, i.e. necking that indicates strain localization. By implementing finite element analysis (FEA), it was shown that the rupture is dominated not by the fracture criterion of material but by the initiation of strain localization that is a deformation characteristic of the material. These ruptures are due to the rapid increase in local strain after the initiation of strain localization and suddenly reach the fracture criterion. For the evaluation of the deformability of the bends, a method based on FEA that can predict the displacement at the rupture is proposed. We show that the yield surface shape and the true stress-strain relationship after uniform elongation have to be defined on the basis of the actual properties of the bend material. The von Mises yield criterion, which is commonly used in cases of elastic-plastic FEA, could not predict the rupture and overestimated the deformability. In contrast, a yield surface obtained by performing tensile tests on a biaxial specimen could predict the rupture. The prediction of the rupture was accomplished by an inverse calibration method that determined the true stress-strain relationship after uniform elongation.

Joining of plastics and light metals contributes to the reduction of a product weight. In this study, the punching rivet method was applied to joining of an acrylic resin sheet and an aluminum alloy sheet. The punching rivet method can join the sheets without drilling. The riveting process of this method is constituted of the punching process of the sheets using the rivet shank and the fastening process of the sheets using the rivet and the rivet holder. The sheets are fastened by using the plastic deformation of the rivet shank. From the observation of the joints made by the punching rivet method, it was found that the acrylic resin sheet of the joint had no crack and out-of-plane deformation of the joint was small. From the results of the joint strength tests, it was considered that the joint made by the punching rivet method had high strength due to the effect of the pressures on seating faces of the rivet and the rivet holder. As a result, the punching rivet method was effective to join the acrylic resin sheet and the aluminum alloy sheet.

This paper described the tensile strength of friction welded joint between Al-Mg alloy (JIS A5052) and pure copper (OFC). In particular, the joining phenomena during the friction process and the effects of friction welding condition such as friction pressure, friction time and forge pressure on the joint strength have been investigated, and the metallurgical characteristics of joints have been also observed and analyzed. The adjacent region of the weld interface at the A5052 side was upset during the friction process, although that of the OFC side was hardly upset. When the joint was made with a friction pressure of 30 MPa, all joints fractured at the weld interface because those joints had the not-joined region at this portion. To reduce the not-joined region, the joint was made with increasing forge pressure. All joints did not have a joint efficiency of 100% (same tensile strength as the A5052 base metal) and the fracture on the A5052 base metal without crack at the weld interface, although the joint efficiency increased with increasing forge pressure. It was showed that the joint had the mechanically mixed layer as the lamellar structures of A5052 and OFC on the adjacent region of the weld interface at the A5052 side, and that layer influenced to the fractured point of the joint. The mechanically mixed layer decreased with decreasing friction time and with decreasing friction pressure after the initial peak. Then, the joint, which had the same tensile strength as the A5052 base metal, the fracture on the A5052 base metal with no crack at the weld interface, and less mechanically mixed layer with no the intermetallic compound (IMC) interlayer on the weld interface, could be successfully achieved. In conclusion, it was suggested that the joint should be made with a low friction pressures such as 20 MPa to prevent generating of the mechanically mixed layer, an opportune friction time such as 6.0 s without generating the IMC interlayer, and a high forge pressure such as 240 MPa in order to achieve completely joining of the weld interface and the fracture on the A5052 base metal.

This paper describes the joint strength of low carbon steel joints and the selection guide of friction welding conditions for low force requirements, which was made by friction stud welding. When joints were made at a friction pressure of 30 MPa with a forge pressure of 30 MPa, all joints did not have the fracture on the base metal. All joints, which were made with a friction time of 1.5 s (just after the initial peak) and a forge pressure of 60 MPa, had the fracture on the base metal. However, all joints with a long friction time such as 5.0 s did not have the fracture on the base metal. Furthermore, when joints were made with a friction pressure of 10 MPa, the joint efficiency of 100% was not successfully achieved regardless of increasing forge pressure. The cause of the joint with the fracture between the initial weld interface and the base metal was that the peripheral portion of that interface of the stud side (small diameter side) was not completely joined with low friction pressure such as 10 MPa. On the other hand, the fracture on the base metal and the joint efficiency of 100% were successfully achieved when joints were made at a friction pressure of 60 MPa, a friction time of 0.6 s (just after the initial peak), and a forge pressure of 60 MPa. All those joints with flash at the initial weld interface had the fracture on the base metal, and it also had the bend ductility of over 15 degrees with no cracking at the initial weld interface by impact shock bending test. However, all joints with a long friction time such as 5.0 s in this friction pressure did not also have the fracture on the base metal. Hence, to obtain the joint possessing the fracture on the base metal with no cracking at the initial weld interface, the joint should be made with a friction pressure of 60 MPa and a friction time of 0.6 s, i.e. an optimum friction pressure and friction time such as the friction torque reached to just after the initial peak. By setting to this condition, the forge pressure will be able to set up the identical friction pressure.

In order to ensure the safety of passengers in the event of an accident, side member and crash box are mounted on automobiles. Cylindrical tubes, rectangular pipes and hat-shaped members have been examined as structural members that subjected to an axial compressive load. However, these structures have problems that the initial peak load is very high and the load rapidly decreases due to buckling during crushing. To solve the problems, we proposed a cellular solid with mimetic woody structure as a new structural member. Some woods have no initial sharp peak load and have a plateau region which the load is constant in the relationship between the load and the displacement, when the impulsive load are applied to them. We considered that those features were suitable for structural members like a side member or a crash box. The basic cell was a square block with a side length of 10 millimeters and it had a hole in the center. The cellular solid was constituted by combining some basic cells. Therefore, a homogeneous cellular solid was fabricated by making small holes in the aluminum cube. From results obtained from the impact crushing test and simulation by the FEM software LS-DYNA^®, it was demonstrated that the proposed cellular solid had crushing characteristics similar to the wood, and the energy absorption characteristics were influenced by the shape and arrangement of the cells. As a result, it was shown that the results of experiment and analysis substantially corresponded. Since the load during crushing depended on the shape and arrangement of the cells, the possibility of controlling the energy absorption characteristics was shown.

This paper described the tensile strength of friction welded joint between Al-Mg alloy (JIS A5052) and pure copper (OFC). In particular, the joining phenomena during the friction process and the effects of friction welding condition such as friction pressure, friction time and forge pressure on the joint strength have been investigated, and the metallurgical characteristics of joints have been also observed and analyzed. The adjacent region of the weld interface at the A5052 side was upset during the friction process, although that of the OFC side was hardly upset. When the joint was made with a friction pressure of 30MPa, all joints fractured at the weld interface because those joints had the not-joined region at this portion. To reduce the not-joined region, the joint was made with increasing forge pressure. All joints did not have a joint efficiency of 100% (same tensile strength as the A5052 base metal) and the fracture on the A5052 base metal without crack at the weld interface, although the joint efficiency increased with increasing forge pressure. It was showed that the joint had the mechanically mixed layer as the lamellar structures of A5052 and OFC on the adjacent region of the weld interface at the A5052 side, and that layer influenced to the fractured point of the joint. The mechanically mixed layer decreased with decreasing friction time and with decreasing friction pressure after the initial peak. Then, the joint, which had the same tensile strength as the A5052 base metal, the fracture on the A5052 base metal with no crack at the weld interface, and less mechanically mixed layer with no the intermetallic compound (IMC) interlayer on the weld interface, could be successfully achieved. In conclusion, it was suggested that the joint should be made with a low friction pressures such as 20MPa to prevent generating of the mechanically mixed layer, an opportune friction time such as 6.0s without generating the IMC interlayer, and a high forge pressure such as 240MPa in order to achieve completely joining of the weld interface and the fracture on the A5052 base metal.

Dissimilar metal joints have some advantages such as high functionality characteristics for the industrial usage. This paper describes the effect of friction welding condition on joining phenomena, tensile strength, and bend ductility of friction welded joints between Al-Mg-Si alloy (AA6063) and austenitic stainless steel (AISI 304). When joints were made at a friction pressure of 30 MPa with a friction speed of 27.5 s^-1, the upsetting (deformation) occurred at the AA6063 side. The temperature on the weld interface increased with friction time, and it reached to 623 K or over at a friction time of 1.5 s or longer. When joints were made with a friction time of 1.5 s and a forge pressure of 240 MPa, all joints had the joint efficiency of approximately 100% and the fracture in the AA6063 base metal. Furthermore, those joints had the bend ductility of 90° in a single direction with no crack at the weld interface and did not have the intermetallic compound (IMC) interlayer on the weld interface. To obtain 100% joint efficiency with good joint, the joint should be made with the following conditions: a high forge pressure such as 240 MPa, the opportune friction time that the temperature on the weld interface reached to about 623 K or higher.

Aluminium (Al) and stainless steel have such some advantages as high functionalities for the industrial usage. However, the dissimilar joints have severe problems such as generating the intermediate layer consisting of a brittle intermetallic compound (IMC interlayer) during welding process. Friction welding is very useful for making of dissimilar joint. This paper described the effect of friction welding condition on joining phenomena, tensile strength, and bend ductility of friction welded joints between pure Al (CP-Al) and austenitic stainless steel (AISI 304). The joining phenomena during the friction process such as joining behaviour, friction torque, temperature changes at the weld interface, and transitional changes of the weld interface were investigated. The effects of friction time and forge pressure on the tensile strength and bend ductility of joints were also investigated, and the metallurgical characteristics of those were observed. The joint, which had high joint efficiency, the fracture on the CP-Al side with no crack at the weld interface, and no IMC interlayer on the weld interface, could be successfully achieved. Then, the joint should be made with a high forge pressure of 150 MPa, the opportune friction time at which the temperature on the weld interface reached about 573 K or higher, and those friction welding conditions were suggested for obtaining good joints with high joint efficiency and the bend ductility of 90 degrees.

Dissimilar metal joints (dissimilar joints) have such several advantages as high functionalities for the industrial usage. However, the dissimilar joints have severe problems such as generating the intermediate layer consisting of a brittle intermetallic compound (IMC interlayer) during welding process. Friction welding is very useful for making of dissimilar joint. This paper described the joining phenomena and the tensile strength of friction welded joint between titanium alloy (Ti-6Al-4V) and low carbon steel (LCS). The joining phenomena during the friction process such as joining behavior, friction torque, and temperature changes at the weld interface were measured. The effects of friction pressure, friction time and forge pressure on the joint strength were also investigated, and the metallurgical characteristics of joints were observed and analyzed. Then, the joint, which had 100% joint efficiency, the fracture on the LCS base metal with no crack at the weld interface, and no IMC interlayer on the weld interface, could be successfully achieved. It was suggested that the joint should be made with high friction pressure, opportune friction time to prevent generating of the IMC interlayer, and with high forge pressure in order to achieve completely joining of the weld interface.

This paper describes the joint properties of the friction welded joint between 6061 (AA6061) Al alloy pipe and Al-Si12CuNi (AC8A) Al cast alloy pipe. When joints were made with a friction pressure of 25 MPa, a friction speed of 27.5 rps, and a forge pressure of 30 MPa, the joint strength increased with increasing friction time, and it was approximately 40 % of the ultimate tensile strength of the AC8A base metal at a friction time of 2.0 s. However, all joints fractured at the weld interface between the AA6061 side and the AC8A side, which had an AC8A adhering to the weld interface on the AA6061 side (mixed-mode fracture). When joints were made at a friction time of 0.3 s with the same friction pressure and friction speed, the joint strength increased with increasing forge pressure, and it was approximately 60 % of the AC8A base metal at a forge pressure of 175 MPa. Many joints had the fracture at the AC8A side although one of the joints had at the mixed-mode fracture. On the other hand, when joints were made at friction times of 0.7 and 2.0 s, the joint strength was approximately 60 % of the AC8A base metal at a forge pressure of 75 MPa. Those joints fractured on the AC8A side, because the adjacent region of the weld interface was softened. In addition, the flash of the joint with a friction time of 0.7 s was fewer than that of 2.0 s. To obtain the joint with the fracture from the AC8A side, the joint should be made with the opportune friction time such as 0.7 s and the opportune forge pressure such as 75 MPa because this joint had no cracks at the weld interface.

The characteristics of friction-welded joint between commercially pure-titanium (CP-Ti) and low carbon steel, of which was subjected to post-weld heat-treatment (PWHT), was investigated. When the joint was made with friction speed of 25 s^-1, friction pressure of 200 MPa, friction time of 2.5 s and forge pressure of 250 MPa, it had the same tensile strength as that of the CP-Ti base metal. The joint had no intermediate layer consisting of intermetallic compound (IMC interlayer) at the weld interface. The joint efficiency of the joint subjected to PWHT decreased with increasing heating temperature and its holding time, and the joint fractured at the weld interface although it had no IMC interlayer. The void was generated on the weld interface of the joint during PWHT process.

This paper describes the effect of friction welding condition on joint properties of austenitic stainless steel (SUS304) joints, which was made by friction stud welding. When the joint was made at a friction pressure of 30MPa with a forge pressure of 30 MPa, the joint efficiency of 100% was not successfully achieved. The joint with a forge pressure of 270 MPa was not obtained the fracture in the base metal, although the joint efficiency increased. The cause of the joint with the fracture between the weld interface and the base metal was that the peripheral portion of the weld interface of the stud side was not completely joined at this friction pressure. On the other hand, the fracture on the base metal and the joint efficiency of 100% were successfully achieved when the joint was made at a friction pressure of 90 MPa and a friction time of 0.3 s (just after the initial peak) with a forge pressure of 240 MPa or higher. This joint had the bend ductility of over 90 degrees with no crack at the weld interface by three-point bending test, and it also had that of over 45 degrees with no crack at the weld interface by impact shock bending test. In conclusion, to obtain the joint efficiency of 100% and the fracture in the base metal with no cracking at the weld interface, the joint must be made with high friction pressure, opportune friction time such as the friction torque reached to just after the initial peak, and with adding high forge pressure.

The joint characteristics of thin-walled pipe friction-welded joint between AA6063 aluminum alloy (A6063) and AISI 304 stainless steel (SUS304) were investigated. The pipe had a thickness of 1.5 mm, and the joint was made with a friction speed of 27.5 rps and a friction pressure of 30 MPa. The joint, which was made by a continuous drive friction welding machine, had heavy deformation on the A6063 side during braking. To prevent deformation until rotation stop with braking, the joint was made by a technique in which the relative speed between both specimens instantly decreased to 0 when the setting friction time was finished, and consequently, the joining could be successfully achieved. The joint with a friction pressure of 30 MPa and a friction time of 0.4 s did not have the intermetallic compound (IMC) layer (interlayer) at the weld interface, although that with a friction time of 1.6 s had it. However, the joint with a forge pressure of 150 MPa had the A6063 side buckling. Moreover, the joint efficiency of the joint with flash was higher than that of the joint without flash because the inner flash of A6063 was stuck to the inner surface of the SUS304 side. Therefore, the joint should be made with the opportune friction time without the IMC interlayer and with the opportune forge pressure without buckling, and the accurate joint efficiency should be evaluated without flash.

The present paper described the investigation of the joint properties of friction welded joint between pure magnesium (CP-Mg) and pure aluminium (CP-Al) with post-weld heat treatment (PWHT). The joint in as-welded condition fractured from the adjacent region of the weld interface, although that had the same strength as the tensile strength of the CP-Al base metal. This joint had the intermediate layer (interlayer) consisting of intermetallic compound (IMC) on the weld interface, and its thickness was below approximately 1 μm. Most of joints subjected to PWHT autogenously fractured at IMC interlayer and that mainly occurred between Mg₂Al₃ and Mg₁₇Al₂ although those layers had a little each other at the fractured surfaces. The IMC interlayer grew to (P-Mg and CP-Al sides, and its thickness increased with increasing heating temperature and/or heating time. The main reasons for the autogenous fracture from the adjacent region of the weld interface of the joint were considered the growth of IMC interlayer of the joint during PWHT process. Furthermore, that fracture of the joint was thought the generating of the thermal stresses in the radial and/or circumferential directions during the cooling stage of PWHT process.

This paper describes the characteristics of friction welding between a solid bar of 6061 Al alloy and a pipe of Al-Si12CuNi (AC8A) Al cast alloy. When the joint was made by a continuous drive friction welding machine (conventional method), the AC8A portion of the joint showed heavy deformation and the AA6061 showed minimal deformation. In particular, the joint could not be successfully made with following conditions, because AC8A pipe side crushed due to insufficient friction heat or high pressure: a short friction time such as 0.3 s, high friction pressure such as 100 MPa, or high forge pressure such as 150 MPa. The heavy deformation of AC8A side was caused by increasing friction torque during braking. To prevent braking deformation until rotation stops, a joint was made by a continuous drive friction welding machine that has an electromagnetic clutch. When the clutch was released, the relative speed between both specimens simultaneously decreased to zero. When the joint was made with friction pressure of 25 MPa, friction time of 0.3 s, and forge pressure of 125 MPa, the joining could be successfully achieved and that had approximately 16% efficiency. In addition, when the joint was made with friction pressure of 25 MPa, friction time of 0.7 s, and forge pressure of 125 MPa, it had approximately 54% efficiency. However, all joints showed the fracture between the traveled weld interface and the AC8A side, because the weld interface traveled in the longitudinal direction of AC8A side from the first contacted position of both weld faying surfaces. Hence, it was clarified that the friction welding between a solid bar of AA6061 and a cast pipe of AC8A was not desirable since the traveling phenomena of the weld interface were caused by the combination of the shapes of the friction welding specimens.

Crash safety of a vehicle is based on impact energy absorbed by crashing the structure in a situation that a cabin is protected. Side impact is extremely dangerous for passengers of vehicles. Energy absorption capabilities of the vehicle in side impact are low because there is little room for large deformation of the safety element to absorb impact energy. On the other hand, weight reduction of the vehicle is also important for the fuel efficiency. The purpose of this study is to develop a light and effective energy absorbing member for side impact. In this paper, an energy absorbing tubular member made by a combination of a thin-walled circular tube and a thin-walled square tube was proposed. The effect of the cross-sectional shape of the tubular member on energy absorption capacities under bending impact was investigated by the experiment and the analysis of the finite element code LS-DYNA. From the obtained results, bending strength decreased significantly when the cross section of the member which was subjected to impact bending load was crushed in flat shape. Therefore, energy absorption capacities were able to be improved by preventing flattening deformation of the cross section. Energy absorption capacities of the tubular member were able to be improved by changing its cross-sectional shape without increasing of the weight.

This paper describes the effect of the inclination of the weld faying surface on joint strength of friction welded joint and its allowable limit for austenitic stainless steel (SUS304) solid bar similar diameter combination. In this case, the specimen was prepared with the inclination of the weld faying surface pursuant to the JIS Z 3607, and the joint was made with that diameter of 12 mm, a friction speed of 27.5 s^-1, and a friction pressure of 30 MPa. The initial peak torque decreased with increasing inclination of the weld faying surface, and then the elapsed time for the initial peak increased with increasing that inclination. However, the steady torque was kept constant in spite of the inclination of the weld faying surface increasing. The joints without the inclination of the weld faying surface, which were made with friction times of 1.5 and 2.0 s with a forge pressure of 270 MPa, had achieved 100% joint efficiency with the base metal fracture. Those joints had 90 degrees bend ductility with no crack at the weld interface. The joints with the inclination of the weld faying surface of 0.3 mm (gap length of 0.6 mm), which were allowable distance, was also obtained the same result with this condition. Furthermore, those joints with a friction time of 2.5 s were obtained the same result. On the other hand, the joints with the inclination of the weld faying surface of 0.6 mm (gap length of 1.2 mm), which was twice inclination of the allowable distance, were also obtained the same result in a friction time of 2.5 s. However, the joints without the inclination of the weld faying surface at this friction time were not obtained the base metal fracture, although those achieved 100% joint efficiency. In conclusion, to obtain 100% joint efficiency and the base metal fracture with no cracking at the weld interface, the joint must be made with the inclination of the weld faying surface, which was allowable distance pursuant to the JIS Z 3607.

This paper described the thermal stress and fracture of friction-welded joint between pure nickel (Ni) and pure aluminum (Al) with post-weld heat treatment (PWHT). FEM model of the joint with the NiAl interlayer at the weld interface, of which was generated as the intermediate layer consisting of intermetallic compound, was constructed. Then, FEM thermal elastic–plastic analysis was carried out, and the fracture factor of the joint during the cooling process after PWHT was described from the calculation and experimental results. The calculated thermal stresses at the adjacent region of the weld interface for the joint, due to the difference of material properties between both base metals, occurred at the early stage during the cooling process. However, the thermal stress was relatively low and had a little effect on the joint fracture. All thermal stresses of the joint with the NiAl interlayer width of 200 μm were smaller than those of 20 μm. Actually, the joint fractured between NiAl interlayer and Al side, of which was like as disbonding in the experiment. Hence, one of the main reasons for the fracture of the joint was able to be thought that the bonding strength between NiAl interlayer and Al side decreased with increasing NiAl layer width, because the thermal stress was low. Therefore, the fracture portion will be changed according to combinations of both base metals to be joined for dissimilar friction-welded joints.

This paper describes the joining phenomena and the tensile strength of friction welded joint between type 1070 pure aluminum (CP-Al) and oxygen free copper (OFC). When the joint was made at a friction pressure of 30 MPa with a friction speed of 27.5 s^-1, the upsetting (deformation) occurred at the CP-Al side. When the joint was made at a friction time of 2.0 s, the whole weld interface on the OFC side had the transferred CP-Al, and it was obtained approximately 30% joint efficiency. Then, the joint efficiency increased with increasing friction time, and it was obtained approximately 63% joint efficiency at a friction time of 12.0 s. The joint fractured at the weld interface, which had a CP-Al adhering to the weld interface on the OFC side. When the joint was made with friction times of 2.0 s and 6.0 s, the joint efficiency increased with increasing forge pressure and then the joint was obtained the CP-Al side fracture at a forge pressure of 135 MPa or higher. However, the joint did not achieve 100% joint efficiency because the adjacent region of the weld interface at the CP-Al side was softened. In addition, the joint at a friction time of 2.0 s had no intermetallic compound (IMC) layer at the weld interface although the not-joined region was slightly observed. On the other hand, the joint at a friction time of 6.0 s did not have the not-joined region at the weld interface although the IMC layer was slightly observed. In conclusion, to obtain higher joint efficiency with fracture on the CP-Al side, the joint should be made with higher forge pressure, and with the suitable friction time at which the entire weld interface of the OFC side had the transferred CP-Al.

This paper described the effect of friction welding condition on joining phenomena and tensile strength of ABS resin friction welded joint. When the joint was made with a friction speed of 4.2 s^-1 and a friction pressure of 0.3 MPa, the temperature at the weld interface at a friction time of about 45 s or longer exceeded 130 ℃. That is, the temperature at the weld interface of the ABS resin friction welding exceeded the glass transition temperature of its resin. When the joint was made with a friction time of 60.0 s, it obtained approximately 67% joint efficiency. However, the joint efficiency decreased with increasing friction speed, and it also decreased with decreasing friction speed. The joint efficiencies with other friction pressures showed a similar change although the friction speed differed. When the joint was made with a friction speed of 2.5 s^-1, a friction pressure of 0.3 MPa and a friction time of 180.0 s, it obtained over approximately 90% joint efficiency. However, the joint efficiency decreased with increasing friction time, and it also decreased with decreasing friction time. Furthermore, the joint efficiency increased with decreasing parallel part diameter of the joint tensile test specimen, and that achieved 95% joint efficiency. In conclusion, to obtain the higher joint efficiency, the joint should be made with opportune friction speed, friction pressure and friction time, and the friction welding should be completed when the whole weld interface became melting state.

This paper describes the joining phenomena and the tensile strength of friction welded joint between type 1070 pure aluminum (CP-Al) and oxygen free copper (OFC). When the joint was made at a friction pressure of 30 MPa with a friction speed of 27.5 s^-1, the upsetting (deformation) occurred at the CP-Al side. When the joint was made at a friction time of 2.0 s, the whole weld interface on the OFC side had the transferred CP-Al, and it was obtained approximately 30% joint efficiency. Then, the joint efficiency increased with increasing friction time, and it was obtained approximately 63% joint efficiency at a friction time of 12.0 s. The joint fractured at the weld interface, which had a CP-Al adhering to the weld interface on the OFC side. When the joint was made with friction times of 2.0 s and 6.0 s, the joint efficiency increased with increasing forge pressure and then the joint was obtained the CP-Al side fracture at a forge pressure of 135 MPa or higher. However, the joint did not achieve 100% joint efficiency because the adjacent region of the weld interface at the CP-Al side was softened. In addition, the joint at a friction time of 2.0 s had no intermetallic compound (IMC) layer at the weld interface although the not-joined region was slightly observed. On the other hand, the joint at a friction time of 6.0 s did not have the not-joined region at the weld interface although the IMC layer was slightly observed. In conclusion, to obtain higher joint efficiency with fracture on the CP-Al side, the joint should be made with higher forge pressure, and with the suitable friction time at which the entire weld interface of the OFC side had the transferred CP-Al.

The present paper described the investigation of the fracture of friction welded joint between pure nickel (Ni) and pure aluminium (Al) with post-weld heat treatment (PWHT). Most of joints autogenously fractured from the adjacent portion of the intermediate layer (interlayer) consisting of intermetallic compound (IMC) on the weld interface due to growing of that after long heating time during the cooling process after PWHT. The IMC interlayer was composed with mainly NiAl, and that grew at the weld interface with PWHT. The joint fracture temperature increased with increasing width of the IMC interlayer in the axial direction of the joint. That is, the fracture of the joint occurred at the interface between NiAl layer and Al base metal. The fractured surface was covered with a little Ni₂Al₃ and/or NiAl₃, and that was like as disbonding. Furthermore, when the width of the IMC interlayer was smaller than approximately 40 μm, the joint fracture temperature of the joint was under about 470 K. However, when the width of the IMC interlayer exceeded 50 μm, the joint fracture temperature drastically increased up to about 800 K. Hence, it was able to be estimate that the joint fracture temperature increased with increasing width of the IMC interlayer. Therefore, one of the main reasons for the fracture of the joint could be concluded as remarkable decreasing of the bonding strength between NiAl layer and Al base metal, which was produced with PWHT.

This paper describes the effect of the friction welding condition on the joining phenomena and the tensile strength of friction welded joint between pure titanium (P-Ti) and low carbon steel (LCS). The adjacent region of the weld interface at the P-Ti side was intensely upsetting with accompanied large deformation of itself when the joint had sparkle at both applied friction pressures of 30 and 90 MPa, although that of the LCS side was hardly upset. The temperature of the whole weld interface at a friction pressure of 30 MPa reached to 1150 K or over at a friction time of 3.0 s or longer. However, the half radius and centreline portion temperatures of the weld interface at a friction pressure of 90 MPa was not reached to 1150 K, although the periphery portion of that was reached to its temperature. The central portion of the weld interface at a friction pressure of 90 MPa was deformed to a convex shape from the viewpoint of the P-Ti side, although that of 30 MPa remained almost flat after when the friction torque reached the initial peak. When the joint was made at a friction pressure of 30 MPa, a friction time of 3.0 s or longer, and a forge pressure of 270 MPa or higher, it achieved 100% joint efficiency and the P-Ti base metal fracture with no crack at the weld interface. However, many joints at friction times of 1.2 and 1.5 s fractured at the weld interface, although those achieved 100% joint efficiency, because whole weld interface temperature was below 1150 K. On the other hand, many joints at a friction pressure of 90 MPa with high forge pressure also fractured at the weld interface, although those achieved 100% joint efficiency, because the weld interface temperature at the half radius and periphery portions was below 1150 K. Those joints did not have the intermetallic compound layer at the weld interface. The difference of the fractured portion of the joint in both applied friction pressures was due to the difference between the maximum temperature at the weld interface during the friction process and the deformation amount of the LCS side caused by applied forge pressure. To obtain 100% joint efficiency with the P-Ti base metal fracture with no crack at the weld interface, the joint should be made with high forge pressure, low friction pressure, and with opportune friction time at which the temperature at whole weld interface reached around 1150 K.