MECHANICAL-PROPERTIES AND SUPERPLASTICITY OF ALZNMG ALLOYS WITH COPPER AND ZIRCONIUM ADDITIONS

The effect of copper and zirconium upon the high-temperature mechanica l properties and the deformation mechanisms of Al-5.7 wt% Zn-2.0 wt% M g alloys is studied. Results of impression creep and tensile tests sho w that the addition of Cu increases the strength of the material, and strongly enhances dynamic recovery during high-temperature deformation . In the case of the ternary AlZnMg alloy the main rate-controlling pr ocess is viscous glide, but in the alloy containing 1.4 wt% addition o f Cu the strain rate is controlled by dislocation climb (10(-6) s(-1) < e < 10(-2) s(-1) and 400 degrees C < T < 520 degrees C). The additio n of 0.14 wt% Zr to the AlZnMgCu alloy results in a fine-grained micro structure due to which the material exhibits superplastic properties a t high temperatures with grain boundary sliding as the dominant proces s during superplastic deformation.