The Effect of Cycling Process Between −196 and 120 °C on Microstructure and Properties of Additively Manufactured 7050 Al Alloy

Wire arc additively manufactured (WAAM) aluminum alloys have been applied in the aerospace field. However, there was a lack of research on the stability of additive components under high- and low-temperature cycling conditions in space. This study focuses on the evolution of microstructure, defects, and mechanical properties of WAAM 7050 aluminum alloy during high- and low-temperature cycling from −196 to 120 °C. The number of cycles is 1, 2, 5, and 10, and one cycle time is 100 min. The results show that the number of η nanophases increase significantly after 5 cycles, and the η′ phases precipitate after 10 cycles. In defects, the porosity increases to 4 times of the as-deposited state after 10 cycles, and the mean equivalent diameter of micropores is stabilized at 0.77 μm. In mechanical properties, the ultimate tensile strength decreases gradually with the increase of cycle times, and the hardness reaches the maximum of 143.2 HV after 5 cycles. The number of micropores increases after 10 cycles, and micropores have a weak effect on the failure mechanism. Cracks tend to sprout and expand along the eutectic phases and pores in the equiaxial grain zones, and equiaxial grain zones are the weak areas when they break.