Microstructural-mechanical property evolution of AA7075 welds with different filler during heat treatment

Abstract

This study investigated the changes in microstructure and mechanical properties of gas tungsten arc welded 7075 aluminum alloy joints using ER5356 and ER7150 filler wire subjected to post-weld heat treatment. The microstructure and mechanical property evolution of the welds was analyzed by both thermodynamics calculations and experimental methods. After welding, alloying elements segregated in the inter-dendritic regions, resulting in the formation of excessive intermetallic compounds. Within the welds of 7075 aluminum alloy with ER5356 filler material, the inter-dendritic region was primarily composed of the T-AlCuMgZn phase. In contrast, in the welds of 7075 aluminum alloy with ER7150 filler material, this region consisted of a eutectic mixture containing α-Al, T-AlCuMgZn, and η-MgZn2 phases. The α-Al matrix experienced limited supersaturation due to the presence of these inter-dendritic intermetallic compounds, which could not dissolve during the post-weld aging treatment. As a comparison, post-weld solutioning and aging treatment significantly improved the ultimate tensile strength of the joints. Among all the samples, the 7075 + ER7150 sample subjected to post-weld solutioning and aging treatment exhibited the highest strength and elongation, primarily attributed to the complete dissolution of the inter-dendritic intermetallic compounds and the formation of fine precipitates.