木村 真晃

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 joint tensile strength of dissimilar carbon steel autocompleting friction welded joint was investigated, that welding method was developed by authors. The easiness of generating the circumferential shear fracture at the groove bottom thickness of the insert piece during the friction process and the joint with the fixed workpiece side fracture were differed, which was caused by the difference for the combination of the insert piece and fixed workpieces.

This paper describes about the joint strength and their improvement of a type 5052 aluminum alloy (A5052) autocompleting friction welded joint, that welding method was developed by authors. When the joint was made at a friction pressure of 60 MPa, it had approximately 75% joint efficiency at a groove bottom thickness of 1.1 mm with an overhanging length of the weld faying surface part (overhanging length) for the fixed workpieces of 15 mm. Those joints had the flexural deformation of the fixed workpiece during the welding, although those had the circumferential shear fracture by the increasing insert thickness with reliability. To reduce the flexural deformation of the fixed workpiece, the joint was made with an overhanging length for the fixed workpieces of 5.0 mm. The joint had 100% joint efficiency with the base metal fracture at a groove bottom thickness of 1.4 mm which was made at a friction pressure of 80 MPa, although that did not achieve 100% joint efficiency at a friction pressure of 60 MPa. In addition, the joint with a groove bottom thickness of 1.3 mm or thin did not achieve 100% joint efficiency, and that with 1.5 mm or thick did not have the circumferential shear fracture. To obtain the generating of the circumferential shear fracture with reliability during the friction process and 100% joint efficiency with the base metal fracture, the joint should be made with thick insert piece, opportune groove bottom thickness of the insert piece, short overhanging length for the fixed workpieces, and relatively high friction pressure.

This paper describes the effect of the friction welding condition and the weld faying surface properties on the tensile strength of the friction welded joint between pure titanium (Ti) and pure copper (OFC). The joint strength of the joint, which was made with the weld faying surface of the Ti side specimen finished with a surface grinding machine, was investigated. The joint did not have 100% efficiency and OFC side fracture regardless of the friction welding conditions. When the joint was made with a friction pressure of 75 MPa, the joint efficiency was approximately 64% regardless of the forge pressures, and all joints fractured at the weld interface, although that efficiency exceeded that of the joints made with other friction pressures. To improve the joint efficiency, one was made with a Ti side specimen whose weld faying surface was finished by buff polishing. The joint efficiency was increased to approximately 85%, although the joint fractured at the weld interface. Moreover, a joint at a friction pressure of 75 MPa with a forge pressure of 270 MPa or higher was obtained with an OFC side fracture, although it did not achieve 100% efficiency. The fact that the joint did not fracture at the OFC base metal was due to the mechanically mixed layer at the weld interface that depended on the maximum height of the Ti side weld faying surface. To clarify the reason why the joint did not achieve 100% joint efficiency, the tensile strength of the OFC base metal with the addition of various compressive stresses was investigated. When the compressive stress was higher than the yield stress of the OFC base metal, its tensile strength was lower than that without a compressive load. Moreover, the tensile strength along the radial direction of the OFC base metal was also slightly lower than that of the longitudinal direction. Hence, the fact that the joint did not also achieve 100% efficiency was due to the decrease in the tensile strength of the OFC base metal by the Bauschinger effect and the difference of the anisotropic property with as-manufactured condition.

This paper describes the effect of the friction welding condition and the weld faying surface properties on the tensile strength of the friction welded joint between pure titanium (Ti) and pure copper (OFC). The joint strength of the joint, which was made with the weld faying surface of the Ti side specimen finished with a surface grinding machine, was investigated. The joint did not have 100% efficiency and OFC side fracture regardless of the friction welding conditions. When the joint was made with a friction pressure of 75MPa, the joint efficiency was approximately 64% regardless of the forge pressures, and all joints fractured at the weld interface, although that efficiency exceeded that of the joints made with other friction pressures. To improve the joint efficiency, one was made with a Ti side specimen whose weld faying surface was finished by buff polishing. The joint efficiency was increased to approximately 85%, although the joint fractured at the weld interface. Moreover, a joint at a friction pressure of 75MPa with a forge pressure of 270MPa or higher was obtained with an OFC side fracture, although it did not achieve 100% efficiency. The fact that the joint did not fracture at the OFC base metal was due to the mechanically mixed layer at the weld interface that depended on the maximum height of the Ti side weld faying surface. To clarify the reason why the joint did not achieve 100% joint efficiency, the tensile strength of the OFC base metal with the addition of various compressive stresses was investigated. When the compressive stress was higher than the yield stress of the OFC base metal, its tensile strength was lower than that without a compressive load. Moreover, the tensile strength along the radial direction of the OFC base metal was also slightly lower than that of the longitudinal direction. Hence, the fact that the joint did not also achieve 100% efficiency was due to the decrease in the tensile strength of the OFC base metal by the Bauschinger effect and the difference of the anisotropic property with as-manufactured condition.

This paper describes an analysis method of the friction torque and weld interface temperature during the friction process for steel friction welding. The joining mechanism model of the friction welding for the wear and seizure stages was constructed from the actual joining phenomena that were obtained by the experiment. The non-steady two-dimensional heat transfer analysis for the friction process was carried out by calculation with FEM code ANSYS. The contact pressure, heat generation quantity, and friction torque during the wear stage were calculated using the coefficient of friction, which was considered as the constant value. The thermal stress was included in the contact pressure. On the other hand, those values during the seizure stage were calculated by introducing the coefficient of seizure, which depended on the seizure temperature. The relationship between the seizure temperature and the relative speed at the weld interface in the seizure stage was determined using the experimental results. In addition, the contact pressure and heat generation quantity, which depended on the relative speed of the weld interface, were solved by taking the friction pressure, the relative speed and the yield strength of the base material into the computational conditions. The calculated friction torque and weld interface temperatures of a low carbon steel joint were equal to the experimental results when friction pressures were 30 and 90 MPa, friction speed was 27.5 s^-1, and weld interface diameter was 12 mm. The calculation results of the initial peak torque and the elapsed time for initial peak torque were also equal to the experimental results under the same conditions. Furthermore, the calculation results of the initial peak torque and the elapsed time for initial peak torque at various friction pressures were equal to the experimental results.

This paper describes the effect of the friction welding condition on the joining phenomena and tensile strength of friction welded joint between pure copper (OFC) and low carbon steel (LCS). When the joint was made at friction pressure of 30 MPa with friction speed of 27.5 s^-1, OFC transferred to the half radius region of the weld interface on the LCS side, and then transferred toward the entire weld interface. The temperatures at the centerline, half radius and periphery portions on the weld interface of the LCS side were almost the same after the initial peak. When the joint was made at a friction time of 2.4 s, i.e. the friction torque was close to the initial peak, that had obtained approximately 40% joint efficiency and fractured from the weld interface with a little OFC adhering to the weld interface on the LCS side. The joint efficiency increased with increasing forge pressure, and it reached approximately 80% at a forge pressure of 180 MPa. This joint fractured at the softened OFC region adjacent to the weld interface. On the other hand, OFC transferred to the peripheral region of the weld interface on the LCS side when the joint was made at friction pressure of 90 MPa with friction speed of 27.5 s^-1. However, OFC transfer was not obtained at the central region because the temperature at the periphery portion was higher than that of the other portions. The joint efficiency increased with increasing friction time, and it obtained approximately 74% at a friction time of 1.2 s. Moreover, all joints fractured between the OFC side and the weld interface, although the joints were made with higher forge pressure. To obtain higher joint efficiency and fracture in the OFC side, the joint should be made with low friction pressure and high forge pressure, and with the friction time at which the friction torque reaches the initial peak.

This paper describes the effect of friction welding condition on joining phenomena and joint strength of pure aluminum (Al) and low carbon steel (LCS) friction welds. When the joint was made with friction pressure of 30MPa, the upsetting (deformation) occurred at the Al base metal. Al transferred to the half radius region of the weld interface on LCS side, and then it transferred toward entire weld interface. When the joint was made with friction time of 0.9s, i.e. the friction torque was close to the initial peak, it had approximately 93% joint efficiency and fractured at Al side. This joint had no intermetallic compound (IMC) at the weld interface. The joint efficiency slightly decreased with increasing friction time. The joint had slight IMC at the weld interface when it was made at friction time of 2.0s. The IMC layer grew to the Al side from LCS side, and it corresponded to Fe₂Al₅ by EDS analysis. To improve the joint efficiency, the joint was made at friction time of 0.9s with increasing forge pressure. However, the joint efficiency decreased with increasing forge pressure, and all joints were fractured at the Al side. Although the joint with forge pressure of 90MPa had hardly softened region, it had approximately 83% joint efficiency. The tensile strength of the Al base metal at room temperature was investigated, that was carried out after various compression loads and temperatures. The tensile strength of it has decreased with increasing compression load under any temperatures. The fact that the joint did not achieve 100% joint efficiency was due to a decrease in tensile strength of the Al base metal by Bauschinger effect. To obtain higher joint efficiency and fracture in Al side, the joint should be made with opportune value without higher forge pressure, and with the friction time at which the friction torque reaches the initial peak.

This paper describes the effect of the friction welding condition on the joining phenomena and tensile strength of friction welded joint between pure copper (OFC) and low carbon steel (LCS). When the joint was made with friction pressure of 30MPa, OFC transferred to the half radius region of the weld interface on the LCS side, and then transferred toward the entire weld interface. The temperatures at the centerline, half radius and periphery portions on the weld interface of the LCS side were almost the same after the initial peak. When the joint was made at a friction time of 2.4s, i.e. the friction torque was close to the initial peak, it had approximately 40% joint efficiency and fractured from the weld interface with a little OFC adhering to the weld interface on the LCS side. The joint efficiency increased with increasing forge pressure, and it reached approximately 80% at a forge pressure of 180MPa. This joint fractured at the softened OFC region adjacent to the weld interface. On the other hand, OFC transferred to the peripheral region of the weld interface on the LCS side when the joint was made with friction pressure of 90MPa. However, OFC transfer was not obtained at the central region because the temperature at the periphery portion was higher than that of the other portions. The joint efficiency increased with increasing friction time, and it obtained approximately 74% at a friction time of 1.2s. Moreover, all joints fractured between the OFC side and the weld interface, although the joints were made with higher forge pressure. To obtain higher joint efficiency and fracture in the OFC side, the joint should be made with low friction pressure and high forge pressure, and with the friction time at which the friction torque reaches the initial peak.

This paper describes the mechanical properties of Al-Mg aluminum alloy (A5052) friction welded joints. Two types of A5052, which have different tensile properties as a result of work hardening treatments denoted by H112 and H34, were used. They were joined by a continuous drive friction welding machine with an electromagnetic clutch in order to prevent braking deformation. That is, the joints were welded by the "Low Heat Input Friction Welding Method" (LHI method), developed by the authors, in which the heat input is lower than in the conventional method. An A5052-H112 joint, which was made at a friction speed of 27.5s^-1, a friction pressure of 30MPa, a friction time of 2.0s (just after the initial peak torque) and a forge pressure of 60MPa, had approximately 95% joint efficiency. To improve the joint efficiency, an A5052-H112 joint was made at a forge pressure of 75MPa, which was the same as the yield strength of the A5052-H112 base metal. It had a 100% joint efficiency and fractured at the A5052-H112 base metal. On the other hand, an A5052-H34 joint was made at a friction speed of 27.5s^-1, a friction pressure of 90MPa, a friction time of 0.3s (just after the initial peak torque) and a forge pressure of 180MPa. It had approximately 93% joint efficiency and fractured at the A5052-H34 base metal. This joint had also a softened region. To improve the joint efficiency, an A5052-H34 joint was made at a forge pressure of 260MPa, which was the same as the ultimate tensile strength of the A5052-H34 base metal. This joint had hardly softened at all, although it had approximately 93% joint efficiency. It was considered that the A5052-H34 joint did not achieve 100% joint efficiency by the difference of the anisotropic properties of the base metal between the radial and longitudinal directions.

This report describes the improvements in the joint properties of friction welded joint of 780MPa class high tensile steel. Welded joint made by a continuous drive friction welding machine, the conventional method, had not obtained 100% joint efficiency despite applying forge pressure. This was due to the softening of the welded interface zone for heat input during braking times. Therefore, we developed a continuous drive friction welding machine with an electromagnetic clutch to prevent heat input during braking time. We proposed the process as "The Low Heat Input Friction Welding Method (the LHI method)". In this case, the joint had the same tensile strength as the base metal at friction time when the friction torque reached the initial peak torque. That is, the welded joint obtained 100% joint efficiency by using only the friction stage up to the initial peak torque without the forge (upsetting) stage, despite the existence of a slightly softened region adjacent to the welded interface. Furthermore, the softened region was hardly generated when this joint was made by applying forge pressure at the initial peak torque. In conclusion, a welded joint of high tensile steel made by only the friction stage of the LHI method had excellent joint properties. The LHI method has a lot of advantages for joining such materials as super fine grain steel with which conventional fusion welding processes have difficulty.

This report describes the properties of friction welded joint of low carbon steel by using Low Heat Input Friction Welding Method (LHI method) that was developed by authors. A direct drive friction welding machine was used for joining. In case of LHI method, the relative speed between both specimens (weld faying surfaces) simultaneously and suddenly decreased to zero at the close of friction time. While the initial seizure and the joining began at the periphery portion by high friction pressure regardless of friction speed, they began at center portion by low friction pressure. The initial seizure was not coincided with the joining under various friction pressures as concerning to above results. However, the friction torque reached to initial peak torque when the welded interface was joined completely and upsetting of both base metals started. The friction welded joints made by LHI method had more than 100% joint efficiency in tensile strength and similar fatigue strength to that of the base metal. That is, there is no necessity for using forging (upsetting) stage. In this case, same results could be obtained in spite of friction pressure. As a conclusion, it was clarified that the welded joints made by LHI method, i.e., without the forging stage, have the same mechanical properties as those welded by the conventional friction welding process including forging stage, regardless of applied friction pressure. Furthermore, LHI method has a lot of advantages for industrial usage, e.g., the machining process of post-weld can be simplified, and so on.

This report describes the observation result of joining phenomena in the friction stage, and an improvement of the conventional friction welding method with similar materials. The materials used were carbon steels and a brake type (direct drive) friction welding machine was used for joining. As the improving friction welding method, relative speed was instantaneously rendered to zero at the end of each friction time. The wear of both surfaces started at periphery portion (outer surface) of the joint and moved to center portion (center axis). Seizure and joining began at center portion and then extended toward periphery portion. The friction torque reached to initial peak torque when the welded interface was joined completely and upsetting of both substrates started. It was determined that friction welded joints with 100% joint efficiency and good bend ductility could be obtained by using only the friction stage up to initial peak torque and without the need for the forging (upsetting) stage. As a conclusion, friction welded joints made without using the forging stage has the same mechanical properties as those welded by the conventional friction welding process including that stage. The friction welding method without forging stage has the advantages of less burn-off (axial shortening) and less burr.