In the present investigation, the microstructure and mechanical characteristics of dissimilar A319
and A356 cast Al alloys plates joined by friction stir welding (FSW) were evaluated. The effect of
tool rotational and welding speeds as well as the post-weld heat treatment (PWHT) on such
properties was investigated. Post-weld heat treatment was carried out at a solutionising
temperature of 540uC for 12 h followed by aging at 155uC for 6 h. For the as welded specimens,
the welded zone (WZ) exhibited higher hardness values when compared with the A319 and A356
parent alloys. The peak hardness at the WZ was found to increase by increasing the tool rotational
speed and/or reducing the welding speed. In contrast, the post-weld heat treated (PWHTed)
specimens exhibited lower hardness values at the WZ than the parent alloys. For PWHTed
specimens, the peak hardness at the WZ was found to decrease by increasing the tool rotational
speed and/or reducing the welding speed. Tensile tests results demonstrate that, for the as
welded specimens, the tensile fracture took place on A356 side where the hardness was minimal.
While for PWHTed specimens, the fracture took place at the WZ. Increasing the tool rotational
speed reducing both tensile and yield strengths, but increases the ductility of the joint.