Microstructure and mechanical properties of friction stir welded duplex Mg–Li alloy LZ91

TLDR: In this article, a light duplex Mg-Li alloy LZ91 with a thickness of 3mm was successfully joined by friction stir welding utilizing a tungsten carbide tool.

Abstract: Superlight duplex Mg–Li alloy LZ91 with a thickness of 3 mm was successfully joined by friction stir welding utilizing a tungsten carbide tool. The microstructures in the stir zone showed refined grains consisting of an equiaxed Mg-rich α phase and a Li-rich β phase. The grains in the Mg-rich α phase showed randomized crystal orientations after dynamic recrystallization. Due to the grain refinement and the random orientation of the Mg-rich α phase, the mechanical properties of the stir zone were optimized, and the hardness of the stir zones were higher than that of the base metal. At the same time, the heat affected zone showed no decrease in its strength. Digital image correlation analyses revealed that the strain in the stir zone and base metal were respectively 0.05 and 0.6 before the samples fractured during the joint tensile tests. Therefore, the joints demonstrated 100% tensile efficiency compared with the base metal.