Abstract: This study examined the effects of heat treatment temperatures (130 °C, 280 °C, 330 °C) on residual stress, mechanical properties, and microstructure of 5A06 aluminum alloy TIG welded joints. Residual stress was measured ultrasonically, mechanical properties were assessed via tensile and hardness tests, and microstructure was characterized using OM and EBSD. Results indicate that 130 °C treatment markedly reduced peak residual stress by 64.4 % while offering good mechanical properties (335.5 MPa tensile strength, 8.5 % elongation). The 330 °C treatment promoted uniform stress distribution and yielded the best mechanical performance (353 MPa, 9.15 % elongation). The 280 °C treatment showed the least improvement. Increasing temperature gradually lowered hardness and transformed the microstructure from recovered state to fully recrystallized equiaxed grains. This work demonstrates that tailored heat treatment can effectively optimize both stress state and overall mechanical properties of 5A06 welded joints.