Abstract: The superplasticity of the Al-Zn-Mg-Zr-RE(alloy A)and Al-Zn-Mg-Ti(alloy B),their change of volume fraction of metastable micro-cavities under various reduction of area and strain rates,as well as the growth of stable cavities in them have been studied by means of small angle X-ray scattering analyses and quantitative metalloraphy respectively.Experimen- tal results show that the volume fraction of metastable micro-cavities of the alloy A is more than that of the alloy B,but the growth rate of stable cavities in alloy A is less than that in al- loy B.Thus,it is believed that the superplasticity of alloy A is superior to that of alloy B.

Key words: Al-Zn-Mg alloy, superplasticity, cavity, strain rate