Achieving high strength-ductility combination and negligible yield asymmetry in extruded AlN/AZ91 composite rods

Abstract

The strength of conventional AZ91-based composites can be usually improved by the extrusion process, however the inadequate ductility is often induced, which limits the practical applications of AZ91-based composites. In this paper, the strength and ductility of AlN/AZ91 composites prepared by in situ synthetic method were significantly improved by a hot extrusion process. Microstructural analysis shows that in-situ AlN particles promoted the recrystallization nucleation and accelerated the recrystallization, resulting in a significant grain refinement in the extruded AlN/AZ91 composites. By the experimental observation, it was found that high density dislocations induced by AlN particles promoted the continuous precipitation of nano-sized γ-Mg17Al12 phases during the hot extrusion. By theoretical calculation and analysis, the contributions of different strengthening mechanisms on the yield strength increment were discussed, which confirmed that the grain boundary strengthening and precipitation strengthening were mainly strengthening mechanisms. By the EBSD-assisted slip trace analysis, it was also confirmed that the higher tensile ductility in the extruded AlN/AZ91 composites was mainly attributed to the activation of pyramidal <c+a> dislocation slip systems. Additionally, a weak basal texture was obtained in the extruded AlN/AZ91 composite rods due to the in-situ formation of AlN particles. Then a negligible tension-compression yield asymmetry in the extruded AlN/AZ91 composites was obtained.