Abstract
The effect of multi-stage aging heat treatments on the hardness, tensile strength, electrical conductance, and exfoliation corrosion (EXCO) resistance of the Al–Zn–Mg–Cu alloy has been studied through the Vickers hardness, tensile, conductivity, and EXCO testing combined with microstructure characterization using a transmission electron microscope. Experimental results demonstrated that multi-stage aging conditions could effectively enhance the localized corrosion resistance through a lower strength loss compared to T6 aging condition (120 °C/24 h). The designed four-step aging (FSA) treatments could improve the EXCO properties to PB degree along with the ultimate tensile strength and yield strength to 373 MPa and 324 MPa, respectively. The development trend of localized corrosion resistances has been further verified using electrochemical impedance spectroscopy and polarization dynamic curves. Microstructures results indicated that dense precipitates in matrix, discontinuous coarse precipitates on grain boundaries, and a proper precipitation free zone play an important role in balancing the strength and corrosion properties of the FSA aged alloy.
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