Design and Research on Al-Zn-Mg-Cu Alloy with Ultra-high Strength and Good Plasticity Matching

Abstract:

An Al-8Zn-3Mg-1.05Cu alloy was designed according to the solid solubility of Zn, Mg and Cu elements in Al matrix. Then, the hot-rolled plate was subjected to solid solution treatment. The results of SEM and XRD show that the solid-solution microstructure with only a small amount of compound residue is obtained after solid solution treatment. Subsequent cold rolling, solid solution and aging treatment of the alloy were carried out. The EBSD results indicate that the alloy obtains incompletely recrystallized structure after cold rolling and solid solution treatment. The KAM diagram shows that the dislocation density in the incompletely recrystallized zone is high. The alloy after solid solution treatment exhibits favorable tensile properties, with the yield strength of 458.61 MPa and elongation of 15.6%. The TEM results after aging treatment show that a large number of fine MgZn₂ phases are precipitated in the microstructure. The average size of MgZn₂ phase is about 6.40 nm, which is notably smaller than that in the reported alloys. After aging treatment, the alloy obtains ultra-high strength and good plasticity with the yield strength and elongation of 729 MPa and 10.37%, respectively. The strength composition of the alloy was calculated, and the precipitation strengthening contribution value of fine MgZn₂ phase is 348.48 MPa. The calculated yield strength value matches well with the experimental value.