Masaaki Kimura

Direct friction welding between type 7075-T6 aluminum alloy (AA7075) and low carbon steel (LCS) is particularly difficult, as cracking often form in the AA7075 flash and propagate to the weld interface during the welding process. This study investigated the simultaneous friction welding of AA7075 and LCS using commercially pure titanium (CP-Ti) as an insert metal in a single-step process, with the aim of achieving a joint free of cracks into the AA7075 flash. The joint free of cracks into the AA7075 flash was not obtained by varying of only the shape of the CP-Ti insert metal. However, flash cracking could be prevented when the weld diameter of the AA7075 side was larger than that diameter of the CP-Ti insert metal, and used with a suitable shape of CP-Ti insert metal having the groove to the AA7075 side. Furthermore, the joint having high tensile strength exceeding the yield strength of the LCS base metal was achieved; specifically, a forge pressure of 400 MPa resulted in approximately 83% of the tensile strength of the LCS base metal. Despite these improvements, the good joint such as fracture occurring within the LCS base metal could not be realized, since the adjacent region of the LCS side is not much deformed even if the joint is made with high forge pressure. Hence, further optimization of the CP-Ti insert metal shape is essential to promote greater deformation of the LCS side and enhance overall joint characteristics.

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.

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.

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.

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.