Influence of pre-strain on the aging hardening effect of the Mg-9.02Zn-1.68Y alloy

Abstract

The solid-solution state Mg-7.68Zn-1.68Y alloy was pre-compressed before the isothermal aging treatment at 200°C, then the pre-induced twinning and its influence on the aging microstructure and aging hardening effect were investigated using EBSD, TEM and SEM. Results showed that: about 15% (area fraction) lenticular (101¯2) tensile twinning were induced into the matrix when the alloy was compressed by 3% pre-strain; and when the amount of pre-strain increased, area fraction of twinning would increase, average size of twinning would decrease, morphology and structure of twinning would change: when the pre-strain reached 15%, about 28% (area fraction) of narrow double twinning (101¯1)-(101¯2)would be induced, while the anamorphosis of double twinning were mostly inter-crossing. In addition, twinning could become an effective substrate for nucleation. And different from precipitates in the matrix, which is rod-shaped β′1-MgZn2 growing along a certain direction, precipitates in the twin boundaries were granular icosahedral quasi-crystal phase with 5-times rotational symmetric diffraction pattern. And when the pre-strain was in the range of 3–15%, aging hardening effect increased with pre-strain; when pre-strain were 10–15%, the peak hardness arrived 110HV, 28% improved compared to that of the not-pre-deformed one (86HV); when the pre-strain exceeded 20%, the aging hardening effect would decrease.