Microstructure and mechanical properties of 6082-T651 aluminum alloy cruciform welded joints

Cruciform welded joints of 15 mm thick 6082-T651 aluminum alloy plates were obtained by metal inert gas welding. The influence of welding parameters on formation of weld, tensile properties and microhardness of cruciform welded joints was studied, and the element distribution in different zones of the joint was analyzed. The results showed that with the increase of wire feeding speed and welding current, the reinforcement of the weld decreased while the penetration and weld width increased. The edge of the weld was a columnar crystal microstructure,and the center of the weld was a mixed microstructure of dendrites and equiaxed crystals. The grain boundary liquation extended from fusion line to the inside of heat-affected zone. Alloy elements such as Mg, Si, Fe and Mn segregated in the weld to form intergranular precipitates.The tensile strength of cruciform welded joints was up to 239 MPa, and the fracture mode was ductile fracture. The microhardness of the joint symmetrically distributed on the web side and the wing side, and the microhardness of the heat-affected zone decreased with the increase of welding heat input, even lower than that of weld zone.