Evolutions of microstructure and mechanical properties for Mg-Al/AlN composites under hot extrusion

Magnesium matrix composites reinforced with 5 wt% AlN particles were fabricated using the hot-pressing sintering followed by hot extrusion. The effects of hot extrusion on the microstructure and mechanical properties were investigated and the strengthening mechanisms of the hot-extruded Mg-Al/AlN composites were presented. The results showed the matrix grain was significantly refined and the uniformity of AlN particles distribution was effectively improved. However, the reinforcement particles were still mainly distributed along the grain boundary after hot extrusion. The remarkable improvement of mechanical properties was primarily attributed to the decreased grain size, improved dispersion of AlN particles and increased dislocation density. The fracture mode changed from layer cracking to mixed fracture with cleaved facets, dimples and fractured particles for the composites under hot extrusion.