Effect of aging plus cryogenic treatment on the machinability of 7075 aluminum alloy

This work aims to explore the effect of aging plus cryogenic treatment on the machinability of 7075 aluminum alloy in high speed cutting. First, 7075 aluminum alloy samples are pretreated by T6 and T6I4. Then they are cryogenically treated under −196°Cfor 168 h. After heat and cryogenic treatment, the samples are experimentally cut at high speed. Samples having received only T6 or T6I4 treatment are selected as the control groups. Surface quality and microstructure evolution are analyzed by SEM, EDS, XRD, TEM, and HRTEM means. The results show that the cutting force of 7075 aluminum alloy is significantly smaller than without cryogenic treatment after cryogenic treatment,; the cutting force of T6-state alloy is 1.25 times as much as the T6I4-state alloy. Under the same cutting parameters, cryogenically treated 7075-T6I4 aluminum alloy has a smaller grain size and contains more precipitates in the aluminum matrix, which are η-MgZn2. The precipitated phase size of T6 is about 80 nm, about 2.5 times that of T6I4.After T6 and T6I4-state samples are cryogenically treated, the alloy precipitate size is about the same as-or slightly smaller than-the grain size of the alloy without cryogenic treatment, but the precipitates are denser and discontinuous. After T6 and T6I4 heat treatment, distinctive stacking fault arises in the machined surface. After cryogenic treatment, the stacking fault is greatly improved.