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

The effect of copper and zirconium upon the high-temperature mechanical properties and the deformation mechanisms of Al-5.7 wt% Zn-2.0 wt% Mg alloys is studied. Results of impression creep and tensile tests show 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 process is viscous glide, but in the alloy containing 1.4 wt% addition of 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 addition of 0.14 wt% Zr to the AlZnMgCu alloy results in a fine-grained microstructure due to which the material exhibits superplastic properties at high temperatures with grain boundary sliding as the dominant process during superplastic deformation.