Microstructure, texture and mechanical properties of friction stir processed Mg-14Gd alloys

Abstract

Mg-14wt% Gd alloys in both as cast and as quenched conditions (T4) were subjected to friction stir processing (FSP). The microstructure evolution, texture modification, mechanical enhancement, as well as subsequent aging performance for both of the two conditions were studied. Supplementary FSP experiments with cold air-cooling (CFSP) were conducted for microstructure evolution comparison. During FSP, the thermal histories are similar in regions away from the top center for both conditions. The primary coarse grains were initially refined through repetition of geometric dynamic recrystallization (GDRX). The refined grains then experienced subsequent recovery and grain growth. Compared with as cast condition, generally larger grain size, lower high angle grain boundary fractions, as well as much stronger texture intensities leading to poorer ductility were generated in T4 condition after FSP. The differences mainly lie on the pinning effect exerted by the Mg5Gd particle remnants. The texture distribution depends on the final position strains and aging has little effect on it.