Effects of natural aging and heat treatments conditions on mechanical properties of dissimilar composite between 6061 Al alloy and Al-Si12CuNi (AC8A) Al cast alloy fabricated by friction welding

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.