Abstract: The softening of heat affected zone (HAZ) inevitably occur after welding of aluminum alloy, especially for heat treatment strengthened aluminum alloy, which leads to the significant decrease of mechanical properties of welded joints. Based on the concept of thermal conductance constrain and local deformation strengthening, a compound technique of welding and rolling for aluminum alloy is proposed, and the effect of the compound technique of tungsten inert gas(TIG) filler wire butt welding with copper pad cooling and rolling on microstructure and mechanical properties of 5083-O and 6061-T6 dissimilar aluminum alloy welded joints is systematically analyzed. The results show that the defect-free and well-formed aluminum alloy butt joints can be obtained by welding-rolling composite forming. The longitudinal and transverse deformations of the welded joints occur simultaneously by rolling. This technique has several advantages over welding alone. These include obvious compaction of weld microstructure, effectively reduction of weld melting zone width, and violent rotation of grain in the heat affected zone (including the solid solution region and the overaging softening region). Compared with the free-cooling welding process, the hardness of the softened zone on the 6061-T6 side of the welded joint with copper pads cooling is increased and the severely softened position is significantly offset to the weld zone. Post-weld rolling greatly increase the overall hardness of the welded joints with two cooling methods. The hardness value at the most severely softened position is increased from 59.5 HV to 84.4 HV, an increase of 41.8%. Compared with free-cooled joints, the tensile strength of the samples by the composite forming with copper pad cooling increases from 197.0 MPa to 288.6 MPa, an increase of 46.5%, which is equivalent to the tensile strength of the 5083-O base material. As well as the elongation is increased from 5.88% to 8.85%. The tensile fracture position is transferred from the 6061-T6 side heat affected zone to the 5083-O side base material.

Key words: aluminum alloy, soften zone in heat affected zone, welding, local deformation strengthening, composite forming