Joint properties of friction welded joint between 6061 Al alloy pipe and Al-Si12CuNi (AC8A) Al cast alloy pipe

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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.