Microstructure and Mechanical Properties of a High-Ductility Al-Zn-Mg-Cu Aluminum Alloy Fabricated by Wire and Arc Additive Manufacturing

Wire and arc additive manufacturing (WAAM) is a feasible technology for manufacturing large-scale metal structures. Nevertheless, this technology is seldom used to fabricate high-performance Al-Zn-Mg-Cu aluminum alloy at present due to its poor machinability and hot cracking sensitivity. 7075 aluminum wires were used herein as a raw material to produce the thin-wall block structure by (cold metal transfer) CMT-WAAM. The microstructure and properties of deposited samples with different orientations were studied compared with traditional cast 7075 aluminum alloy. Results indicate that the microstructure of the deposited samples in the horizontal direction is mainly composed of a small amount of fine columnar crystal structure and equiaxed crystal composition. Most of the grains in the deposition direction layer are coarse equiaxed and a few slender columnar grains. In the process of preparation, the precipitation of the second phase was observed, which was mainly composed of Mg₂Si and (Mg (Zn, Cu, Al)₂) phases. The microhardness and wear resistance of the deposited samples is lower than those of cast 7075 aluminum alloy, while the corrosion resistance is better. The anisotropic microstructure triggers subtle differences in properties with different directions, the tensile strength in the horizontal direction is better than that in the deposition direction, and the elongation in each direction is higher than 30%. The process of dynamic reversion and static recrystallization lead to low dislocation density and increased elongation.