Effect of Cr content on microstructure, mechanical properties and corrosion properties of Al–Zn–Mg–Cu alloys

This study explores the effect of Cr content on the microstructure, mechanical properties, and corrosion behavior of Zr-containing Al–Zn–Mg–Cu alloys. The objective is to elucidate how varying Cr levels influence these characteristics to optimize alloy performance for automotive and aerospace applications. Microstructural analysis was conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). Mechanical properties were evaluated through tensile and hardness testing, while corrosion resistance was assessed via intergranular corrosion (IGC) and exfoliation corrosion (EXCO) tests. The results reveal that Cr addition narrows the precipitation temperature range of the Al₃Zr phase and refines its size and distribution uniformity. Furthermore, Al₇Cr dispersoids effectively hinder recrystallization by obstructing dislocation motion. Under T6 heat treatment, increasing Cr content enhances strength as well as resistance to intergranular and exfoliation corrosion. The alloy containing 0.2 wt% Cr exhibited optimal mechanical properties, with a yield strength of 523.5 MPa, an ultimate tensile strength of 598.2 MPa, and an elongation of 13.99 %. The underlying strengthening mechanisms are also discussed. These findings provide valuable insights for alloy design and industrial applications of 7xxx series aluminum alloys.