Effects of heat treatment on the activated flux TIG-welded AZ31 magnesium alloy joints

The effects of heat treatment on the microstructures and mechanical properties of tungsten inert gas-welded AZ31 magnesium alloy joints with Cr2O3 flux coating were investigated by microstructural observations, microhardness, and tensile tests. The results showed that the activating flux of Cr2O3 improved the weld penetration and the depth/width ratio of the tungsten inert gas-welded AZ31 magnesium alloy joints markedly. Heat treatment (1) eliminated the coarsened network-like beta-Mg-17(Al, Zn)(12) particles which formed in activating tungsten inert gas and (2) resulted in more uniform grain size distribution of partially melted zone. Apart from that, either the microhardness of the seams, the ultimate tensile strength, or the elongation of the welded joints was improved by aging treatment, while too high aging temperature would give rise to a sharply decreased ultimate tensile strength.