Microstructures and mechanical properties of TIG welded Al-Mg2Si alloy joints

In this paper, the microstructures and mechanical properties of tungsten inert gas (TIG) welded joints were studied. Three zones were formed in these joints: a heat-affected zone (HAZ), a partial melting zone (PMZ) and a fusion zone (FZ). In the FZ, the microstructure consisted of only α-Al and eutectic Mg2Si. The α-Al segregation phenomenon occurred when the welding current increased from 125 A to 135 A. The low-angle grain boundaries (LABs) found in the base material (BM) transformed into high-angle grain boundaries (HABs) in the FZ. The texture of the BM was concentrated in three specific preferred orientations, whereas the texture was eliminated in the FZ. The hardness in the FZ was 45 % higher than that in the BM. The eutectic Mg2Si phase in the welded joints became fine and dense, and the needle-like β″ phase in the BM was replaced by a high density of fine precipitates, which led to an increase in hardness. The ultimate tensile strength (UTS) and elongation of the joints welded at 125 A were lower than those of the BM and the joints welded at 135 A. Furthermore, no cracks were generated in the joints after multiple thermal shocks.