Effect of Non-isothermal Cooling Aging on the Microstructure and Properties of Al-Zn-Mg-Cu Alloys

Non-isothermal cooling aging treatment (NCA) of the Al-Zn-Mg-Cu alloy can obtain an excellent comprehensive performance. The properties of the alloy were studied by hardness, friction and wear, intergranular corrosion, spalling corrosion, and electrochemical corrosion, the microstructure of the alloy was observed by transmission electron microscopy, and the relationship between the microstructure evolution and properties of the alloy after cooling aging was analyzed. The results show that after NCA, the number of matrix precipitated phases of the 20-C120 alloy is large and uniformly distributed, and the hardness reaches 188.5 HV, which far exceeds the hardness of the T6 alloy (171.6 HV). The friction coefficient is 0.56, the weight loss is 7.2 mg, and the wear resistance is good. Grain boundary precipitated phases (GBPs) at the grain boundary are intermittently distributed and independently rounded, and width of the precipitation-free zone (PFZ) is 50.1 nm, which destroys the occurrence of corrosion and improves corrosion resistance. The intergranular corrosion depth is 42.3 μm, and the exfoliation corrosion grade is EA, and the i_corr and V_corr are 0.0026 mA/cm² and 0.0844 mm/a, respectively. The comprehensive performance is better than T6 and T76.