Effect of travel speed on the microstructure of Al-to-Mg FSW joints

Abstract

The effect of relatively high travel speed on the microstructure (SEM) and mechanical properties of friction stir welded dissimilar 5754 Al/AZ31Mg alloys has been characterised. With the Al alloy placed on the advancing side, travel speed were varied from 100 to 350 mm min⁻¹ and the mechanical properties of the joint subsequently determined by tensile tests on cross-section samples. The best (but moderate) properties were obtained at 200 mm min⁻¹. The joint failed by brittle fracture along localised bands on the severely deformed Al side containing Al₃Mg₂. The lowest travel speed developed a eutectic Al₁₂Mg₁₇ microstructure. The joint obtained at 100 and 250 mm min⁻¹ failed, by ductile and brittle mixed fracture modes, at the bonding interface containing continuous intermetallic compounds.