Cyclic non-isothermal aging: an aging method to simultaneously improve mechanical properties and corrosion resistance of Al-Zn-Mg-Cu alloys

Abstract

To simultaneously enhance the mechanical properties and corrosion resistance of the Al-Zn-Mg-Cu alloy, a cyclic non-isothermal aging method is suggested as a solution. The impact of repeated temperature changes over time on the overall characteristics and microscopic structure of the Al-Zn-Mg-Cu alloy were examined through hardness test, tensile property test, friction and wear performance test, intergranular corrosion test (IGC), electrochemical corrosion test, and transmission electron microscopy (TEM) observation. According to the findings, the alloy's hardness value reaches its peak at 195.8HV when subjected to 1 cycle. Similarly, the tensile strength reaches its highest point at 620.2 MPa. Additionally, the minimum grinding weight loss is recorded at 6.5 mg, superior mechanical properties surpassing those achieved through T6 aging. Corrosion depth minimized at 18.9 μm, and the corrosion rate is the slowest at 0.0065 mm per year. In addition, the precipitation phase of the alloy's matrix demonstrates the smallest average size, the highest volume fraction, and the most potent precipitation strengthening effect. The grain boundaries exhibit precipitated phases that are uniformly dispersed and have a rounded shape. The width of the Precipitate Free Zone (PFZ) is measured to be 73.1 nm. It efficiently blocks the pathway for anodic corrosion, decelerates the advancement of corrosion, and enhances the resistance to corrosion. The presence of Cu ions in the grain boundary precipitates (GBPs) significantly elevates the electrode potential and enhances the corrosion resistance, surpassing that of T73 aging.