海津 浩一

In a previous study, the tensile strength of dissimilar friction welded joints that was composed between commercially pure Al (AA1070) and low carbon steel (LCS) decreased with increasing forge pressure. This result was not applicable to the general consequence of friction welding. To prevent a decrease in the tensile strength of joints by the increase in forge pressure, the improving method of tensile strength in friction welding was investigated. Two types of AA1070 with different tensile properties due to tempering condition were used, and the weld faying part of the specimen had various overhang lengths and weld diameters. Dissimilar friction welded joints, which were composed with those AA1070 side specimens and LCS specimens, were made with various forge pressures. Then, the relationship between the tensile strength of the joints and the forge pressure was evaluated. The tensile property of AA1070 base metals with various compression stresses was also investigated, and the result was compared with the tensile strength of joints. The decrease in the tensile strength of the friction welded joints with added high forge pressure, which had an AA1070 base metal fracture, could be prevented by changing of the shape at the weld faying part of the specimen and tempering condition of the AA1070 side. However, such a joint should be made with a suitable forge pressure with the AA1070 side fracture and the same tensile strength as that of its base metal since the consideration of the decrease in the tensile strength of joints by greater forge pressure can be ignored.

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.

A6063とFCD400の薄肉円管の接合に摩擦圧接法を用い，継手強度に及ぼす圧接条件の影響を調べた．外径 16mm，内径 12mmとし，摩擦速度27.5s-1，摩擦圧力30MPaで接合した．その結果，摩擦時間0.2s，アプセット圧力165MPaの時にA6063母材に対して継手強度が約76%の引張強度となった．そして，熱処理による脱炭処理を行ったところ，継手強度が約87%まで増加することが分かった

A5052/SUS304摩擦圧接継手に温度を種々変化させて後熱処理を施した．そして，熱処理を施した継手の引張強さを調べた．摩擦圧力30MPa，摩擦時間1.5s，アプセット圧力240MPaとして継手を作製したところ，接合したままではA5052母材に対して約95%の引張強さで圧接面から破断した．一方，熱処理温度の増加にともない継手の引張強さは減少し，475℃～500℃で急激に減少することがわかった．

溶融溶接法では接合が困難である，難燃性Mg合金のAZX611と，Al合金の代表格であるA5083を摩擦圧接法を用いて接合した．A5083側の変形を促し，継手の引張強さを向上させるために，AZX611側に設ける接合端部長さを種々変化させて摩擦圧接を行った．その結果，AZX611側の直径16mm，接合端部長さ25mmの場合，最大でAZX611母材の約65%の引張強さを有した継手を作製することができた．

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.

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.

自動車には交通事故による死傷者を減らすために安全技術が求められており，事故時の安全を確保するために衝撃吸収部材が搭載されている．この衝撃吸収部材が潰れ切るまでの変形量を大きくすることによって従来よりも衝突エネルギー吸収量を増加させるため，折り紙の一種であるミウラ折りを格子状に配したラティス構造体について，支柱の角度や直径を変更して衝撃圧潰解析により比較し，エネルギー吸収性能を検討した．

.空孔セルを有するクラッシュボックス側面にテーパを付けることで，荷重の変動を抑えることができたが，中間 部が緻密化していた．衝突エネルギー吸収量を増加させるため，クラッシュボックス上部から圧潰を進行させ変 位量を増やすことを狙いとし，①クラッシュボックスの高さを変更する②テーパの曲率を変更するという2点につ いて検討を行った．空孔セルを有するクラッシュボックス側面にテーパを付けることで，荷重の変動を抑えることができたが，中間 部が緻密化していた．衝突エネルギー吸収量を増加させるため，クラッシュボックス上部から圧潰を進行させ変 位量を増やすことを狙いとし，①クラッシュボックスの高さを変更する②テーパの曲率を変更するという2点につ いて検討を行った．.

ステントを半径方向に拡張した際に長軸方向に縮小してしまう問題に対して，半径方向に拡張したときに長軸方向にも展開できるステントを目的とし，折紙の折り方の1種であるなまこ折り形状を模擬したステントモデルを作成し，FEMを用いた円周の内側から外側に力を負荷させる解析し，血管内に留置されるステントの拡張の挙動について検討を行った．

スペースデブリの宇宙構造物への衝突に関して，宇宙構造物を防御するために設置される防御バンパーに注目し，防御バンパーをどのようにすればより耐衝撃性能が向上するのかを，三次元SPH解析を用いて検討を行った．

BCC，FCC，オクテットトラス，切頂八面体，菱形十二面体の5種類のラティス構造体について衝撃圧潰解析を行い，衝撃吸収部材として適した構造を検討した．さらに，単位格子の大きさや支柱の太さを変化させた際の衝撃吸収特性に与える影響を調べることで，圧潰中の荷重変動が少なく，大きなエネルギー吸収量を持つ構造を検討した．

脆弱な金属間化合物の生成により，難燃性Mg合金であるAZX611と，Al合金の代表格であるA5083を溶融溶接法で直接接合することは極めて困難であるため，摩擦圧接法で接合した．継手の引張強さを向上させるために，AZX611側に設ける接合端部の形状を変化させ，その一部に段差をつけた形状として摩擦圧接を行った．その結果，AZX611母材の約52%の引張強さを有した継手を作製することができた．

摩擦圧接法を用いてアルミナセラミックスとAC8Aを接合し，継手の強度評価を行った．摩擦速度27.5s-1，摩擦圧力25MPa，アプセット圧力75MPaの一定とし，摩擦時間を種々変化させて実験を行った．その結果，継手はすべてアルミナ側から破断したが，最大でも摩擦時間10.0sの時でAC8A母材の約1.5%という引張強度であり，高い継手強度を得ることができなかった．

A7075と軟鋼の直接摩擦圧接ではA7075側のバリ割れが生じ，これにより継手強度が低下する問題があった．そこで，A7075と軟鋼の両者に対して接合性が良い純Tiを挿入材として摩擦圧接を行った．その結果，本組み合わせでも接合が可能であったが，A7075側にバリ割れが発生する継手もいくつかあった．そこで，このバリ割れを防止するために挿入材のA7075側に張出部を設けて挿入材の形状を種々変化させ，その改善を試みた．

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 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.

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 27.5 s-1, a friction pressure of 20 MPa, a friction time of 1.5 s, and a forge pressure of 270 MPa, 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 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 a-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.

A7075側のバリ割れが生じることから，A7075と軟鋼の直接摩擦圧接では良好な継手を得ることが困難であるため，純Tiを挿入材として摩擦時間と挿入材の形状を種々変化させ接合を行った．その結果，純Tiの挿入材を用いても接合が可能であり，摩擦時間0.5～0.8sの時に最も高い引張強さを得ることができた．しかし，摩擦時間0.8s以降ではA7075のバリ割れが生じる継手もあり，挿入材形状を変更する必要があることが分かった．

A5083とSS400との継手作製に摩擦スタッド接合を適用し，圧接条件を種々変更して接合実験を行った．そして，接合現象を観察するとともに，継手強度に及ぼす圧接条件の影響について調べた．その結果，摩擦圧力60MPaにおいて引張強度が高い継手を得られやすいことが分かった．しかし，引張試験後の継手圧接面を観察したところ，A5083のSS400側への移着量は中心部で少ない傾向にあることも分かった．

アルミナセラミックスと鋳造Al合金(AC8A)との直接接合に摩擦圧接法を適用した．摩擦速度27.5s-1，摩擦圧力25MPa，摩擦時間10.0sの一定条件とし，アプセット圧力を25MPa，50MPa，75MPaと種々変化させて実験を行った．その結果，両者を一体化させることができた．また，アプセット圧力を増加させてもアルミナセラミックス側で粉砕を生じさせることなく継手を作製することができた．

積層造形では，造形した合金の表面が非常に粗いものになることがあるため，積層造形で造形を行ったものと機械加工を施したものでは表面性状に大きな差異を生じることが懸念される．そこで，AlSi12合金を使用して引張試験片形状そのものを造形したものと角材を造形した後に旋盤加工を施したもので強度を比較した．その結果，造形したままの形状よりも旋盤加工を施したもの引張強度が高くなることが分かった．

© 2019, ASM International. 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.

© 2019, Shanghai University and Springer-Verlag GmbH Germany, part of Springer Nature. 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.

© 2019, Springer-Verlag London Ltd., part of Springer Nature. 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.

AZX611とA5083との摩擦圧接継手に関し，直径12mmの同径同士で接合を行った場合，圧接条件を種々変化させて継手を作製しても最大でAZX611母材の約33% の引張強さしか得ることができなかった．しかし，AZX611側の接合端面直径を16mmと大きくして接合を行ったところ，継手はすべて圧接面から破断したものの，AZX611母材に対して約61%の引張強さを得ることができた．

板材と棒材の組み合わせであるスタッド継手は様々な分野で広く用いられている．軟鋼の摩擦スタッド継手については母材破断する良好な継手が得られる圧接条件が見出されているが，負荷する推力が施工現場で容易に出力可能ではなく，圧力を維持したまま推力だけを減少させることが求められている． 本研究ではスタッド側の形状を中実棒から円筒とし，低推力状態で，良好な継手が得られる最適なスタッド形状を検討した．

FCD400（鋳鉄）とA5052（Al合金）の摩擦圧接にて，摩擦圧力を変化させて接合した．90MPaという高い摩擦圧力では鋳鉄側圧接面中心部にAl合金があまり移着していないため，Al合金母材の約53% の引張強さしか得ることができなかった．30MPaという低い摩擦圧力では鋳鉄側圧接面全面にAl合金が移着し，約75%の引張強さが得られた．つまり，低い摩擦圧力の方が継手の引張強度が高いことが分かった．

A6063 とSUS304 の摩擦圧接において，アプセット圧力を変更して接合し，それぞれの継手に種々の条件で熱処理を施した．母材破断した最適圧接条件の継手に熱処理を施しても破断形態は変わらなかったが，圧接面で破断する条件の継手に熱処理を施すとA6063 側から破断することがわかった．また，どちらも熱効果指数がある一定の値を超えると，圧接面に中間層が生成されることで継手強度が著しく低下することもわかった．

A5083 とSS400 との継手作製に摩擦スタッド接合を適用し，圧接条件を種々変更して接合実験を行った．そして，接合現象を観察するとともに，継手強度に及ぼす圧接条件の影響について調べた．その結果，アプセット圧力が高い条件の方が引張強度が高い継手を得られやすいことが分かった．また，引張試験後の継手圧接面を観察したところ，A5083 のSS400 側への移着量は中心部と外周部で差が生じていたことがわかった．