Microstructure and mechanical properties of A7N01-T4 aluminum alloy metal inert gas welded joints filled with self-designed 7A48 aluminum alloy wire

Abstract

7××× aluminum alloy is a metal with a high tendency to weld cracks. In the welding process, 7××× aluminum alloy wire was seldom used but low strength matching 4××× and 5××× aluminum alloy wire was used for joining, which had poor mechanical properties of welded joints. In this paper, a self-designed low copper 7A48 wire containing scandium was used as filler material for metal inert gas (MIG) welding of 4 mm thick A7N01-T4 aluminum alloy plates. The results show that the A7N01-T4 MIG welded joints were obtained with good seam formation and no crack formation. The equiaxed dendrites in the weld zone were found. The precipitated phases were primarily Mg-rich and Zn-rich, forming a typical 7××× aluminum alloy structure. In the fusion zone, fine equiaxial crystals were found, with a width of about 100 μm. In the heat-affected zone, grains growth occurred and the precipitated phase was dissolved or aggregated. The hardness of the WZ reached 81.7% of that of the base material and the softening of the WZ was not significant. The average tensile strength and elongation of the specimens were 364.9 MPa and 17.5%, respectively. The tensile fracture occurred in WZ and the fracture was dominated by microporous aggregation shear fractures with localized cleavage fractures occurring.