Joint Properties of Al-11%Zn-3%Mg-1.4%Cu Alloy by Friction Welding and the Effect of Heat Treatment

The weldability of an Al-11%Zn-3%Mg-1.4%Cu alloy by friction welding was investigated, and the effects of T6 treatment during and after welding on the microstructure and joint properties were clarified. Fine grains were formed at the interface of the as-welded joint and were coarsened by the T6 treatment. eta' phase was coarsened at the interface due to friction welding, on the other hand, fine eta' was precipitated again by T6 treatment after welding. The joint efficiency in tensile tests was 72% for the as-welded joint but recovered to 89% by T6 treatment after friction welding, and all fracture locations were near the interface layer. Tensile strength differed depending on whether the grain elongation direction was parallel or perpendicular to the tensile direction, suggesting that the grain shape near the interface was the cause of joint failure.