Effect of non-isothermal aging on the microstructure and properties of Al-Zn-Mg-Cu alloys

Abstract

In this paper, hardness test, electrochemical corrosion test and intergranular corrosion test were used to study the mechanical properties and corrosion resistance of Al-Zn-Mg-Cu alloy after non-isothermal aging treatment with four different heating rates, and scanning electron microscope and transmission electron microscope were used to study its microstructure changes. The results show that at the heating rate of 20 ℃/h when the specimen temperature is increased from 100 ℃ to 180 ℃(20-H180), its hardness and tensile strength after quenching were enhanced to 183.1 HV and 582 MPa, much better than T6 sample. The results of electrochemical testing show that the self-corrosion current density is 0.0024 mA/cm2 and the corrosion rate is 0.0772 mm/a. The maximum depth of intergranular corrosion is 27.8 µm, which is good corrosion resistance and better than the other three heating rate samples, and comparable to corrosion resistance of T76 sample. The results of transmission electron microscopy show that the precipitated phase in the crystal is dominated by a uniform η' phase, which can improve the hardness and mechanical properties of the matrix, the grain boundary precipitated phase is discontinuous, the PFZ is obvious, and the width is 44.8 nm, improving corrosion performance of the alloy, exceeding the corrosion resistance of T76.