Effect of three-stage homogenization on mechanical properties and stress corrosion cracking of Al-Zn-Mg-Zr alloys

The effect of three-stage homogenization on mechanical properties and stress corrosion cracking of Al-Zn-Mg-Zr alloys has been investigated. The results reveal that the interface of η phases provide the favorable sites for Al3Zr dispersoids under the first-stage homogenization at 350 °C, and therefore three-stage homogenization can reduce size and improve density and homogeneity of Al3Zr dispersoids. Uniform, fine and dense Al3Zr dispersoids inhibit recrystallization effectively and improve the uniformity of the grains. Under the same T74 aging temper, the main strengthening mechanisms of the material are η' phases and dispersion strengthening, and as a result the strength of the material increases by 11.02 MPa and 3.11 MPa when compared with one-stage and two-stage homogenization, respectively. Al3Zr dispersoids can pin dislocations and reduce the accumulation of dislocations at grain boundaries significantly, besides, uniform grains contribute a lot to the elongation, leading to a higher elongation and impact toughness of the material. The improved corrosion resistance is due to a decrease in large-angle grain boundaries which are favorable channels for corrosion, and SCC susceptibility (ISSRT) of the material is only 2.6%.