Development of grain size/ texture graded microstructures through friction stir processing and subsequent cold compression of a rare earth bearing magnesium alloy

Abstract

The present work deals with the effect of mechanical post-treatment on the microstructure and texture evolution of friction stir processed Mg-4.37 wt%Y-2.9 wt%RE-0.3 wt%Zr alloy. In this respect, the stir processed specimens were compressed down to engineering strain of 10 and 20%, and the resultant microstructures were characterized. Through applying subsequent compressive loading, fraction of low angle boundaries was increased, substructure was developed, the grain size was refined, and specified misorientation angles/texture components were faded or appeared. The degrees of such evolutions were different between the surface layer and stir zone, and resulted in development of graded microstructures. The fraction of strain-less and fresh grains was considerably decreased; but the fraction of coarse grains holding high grain orientation speared (GOS) was remarkably increased specially by moving away from material surface. Schmid analysis indicated the higher probability of non-basal slip within the unstable coarse grain in the course of subsequent loading. This was led to the occurrence of post-dynamic recrystallization which was traced through the sequence of substructure development and transformation of the low angle boundaries in to the high angle ones. Such gradual microstructure/texture evolution indicate the stir processing plus compression loading as capable method for fabrication of micro-scale functionally graded materials. • Mechanical post-treatment of friction stir processed WE43 magnesium alloy. • Fabricating graded microstructures regarding grain size, substructure and texture. • Contribution of continuous dynamic recrystallization during friction stir processing. • High potential of unstable coarse grains for refinement during subsequent loading. • Post-dynamic/Meta-dynamic recrystallization activates during subsequent compression.