Mitigation of heat treatment distortion of AA 7075 aluminum alloy by deep cryogenic processing using the Navy C-ring test

Abstract

Abstract Heat treatment is a promising approach to advance the mechanical properties of AA 7075 aluminum alloy for aerospace structural applications. Quenching is commonly performed after solutionizing of AA 7075 aluminum alloy to impart supersaturated solid solution condition. It involves rapid cooling of the previously solutionized part to room temperature with water as a quenching medium. It leads to severe distortion of the structural part and deteriorates its surface integrity due to the high thermal residual stresses. This paper reports the distortion behavior of heat-treated AA 7075 aluminum alloy by implementing the standard Navy C-ring test. For precise measurements, the coordinate measuring machine (CMM) was used. Deep cryogenic treatment (DCT) was executed after conventional heat treatment (CHT) to reduce the tensile residual stresses and mitigate the distortion potential of AA 7075 aluminum alloy. Results showed significant improvement in surface finish and hardness of deep cryogenically treated AA 7075 aluminum alloy. It is attributed to the precipitation of fine spherical second phase particles distributed uniformly in the matrix. The distortion potential of heat-treated AA 7075 aluminum alloy is minimized by 30.7 % by deep cryogenic processing. It is correlated to the counterbalancing of tensile residual stresses in the heat treated part by compressive residual stresses ensued by deep cryogenic quenching.