Study on microstructure and properties of TIG welded joints of dissimilar aluminum alloys SLM-AlSi10Mg and 6061-T6

Butt welding between SLM-formed AlSi10Mg and rolled 6061 alloy (T6 state) was conducted by the tungsten inert-gas arc welding(TIG) method. The microstructure and mechanical properties of TIG welded joints under different current parameters were analyzed using ER4043 filler wire. The results indicate that weld seams with excellent appearance and formation quality are obtained under current parameters of 140 A and 125 A. Near the AlSi10Mg base metal side in the weld seam, pores aggregate and are distributed in a “chain-like” manner, while the porosity on the 6061-T6 side is low. Under low current conditions, the average pore size is small. As the welding current increases, the width of the heat-affected zone on both sides of the weld seam and the grain size in different regions increase accordingly. The microstructure near the AlSi10Mg side of the weld seam consists of equiaxed grains; the 6061-T6 side exhibits columnar grains, and the central region is composed of coarse equiaxed grains. With the increase in welding current, the average microhardness in various regions of the weld seam decreases, and the tensile strength of the welded joint decreases correspondingly. The tensile fracture locations of the welded joints are all situated in the heat affected zone of the 6061-T6 base metal, where precipitated phases aggregate along the grain boundaries, which increases the brittleness of the microstructure. The post-fracture elongation is consistently lower than 4%, and the maximum tensile strength of the TIG welded joint at low current can reach 185 MPa.