Effect of Ni interlayer on microstructure and mechanical properties of Al/Mg dissimilar friction stir welding joints

Abstract

In this work, friction stir welding (FSW) was carried out for the flat butt welding tests of Al/Mg dissimilar alloys by introducing Ni foil interlayer with different thickness. The effect of the thickness of interlayer on microstructure and mechanical properties of the FSW joints was explored. The results revealed that with the increase of the thickness of Ni, the effective bearing area of the weld nugget zone (WNZ) increased. It achieved the maximum value when the thickness of interlayer was 0.3 mm, and a dense ‘onion rings’ structure which was composed of the cross distributions trips of magnesium alloy, aluminium alloy and the intermetallic compounds (IMCs), as well as the Ni particles of varying sizes were formed. Compared to the joint without introducing Ni, the introduction of Ni made the joints generate Mg₂Ni and the Al₃Mg₂ was partially replaced and led to the ultimate tensile strength (UTS) increased by 13.5%.