Effect of micro-alloying elements modification on the microstructure and properties of TIG welded joints of AlMg4.3Mn0.6Cr0.12-H321 alloy

TIG welding tests were carried out on AlMg4.3Mn0.6Cr0.12-H321 alloy with different micro-alloy elements by 5B71 alloy wire, and the effects of micro-alloy elements Zr, Er and Sc on the microstructure, microhardness and mechanical properties of welded joints were systematically studied. The results showed that the base material of AlMg4.3Mn0.6Cr0.12-H321 was demonstrated as strip structure, and the TIG welded zone was demonstrated as equiaxed solidified structure. The addition of trace elements Zr, Er and Sc can form nano-precipitated phase in the base material, which caused pinning dislocation, and inhibited the recrystallization of the alloy. Compared with the addition of Zr alone, the addition of Zr, Er or Zr, Sc can more effectively inhibit the recrystallization behavior of heat affected zone of the joints and reduce the softening of base material during welding. The microhardness of the 5 groups of joints were displayed in W shape symmetrically along the weld center, and reached the lowest in the heat affected zone. Accordingly, the specimens of mechanical tensile were broken in the heat affected zone. The strength of the joint increased gradually with the increase of microalloying element type and the amount of addition. When the Er element was increased to 0.35wt.%, the tensile strength of the weld reached 274 MPa and the welding coefficient was 83.3%. The tensile strength of 5# sample joint with Zr and Sc elements was the highest, which was 293 MPa, and the welding coefficient was 89.7%.