High strength-ductility synergy of MgAlB4 whisker reinforced aluminum matrix composites achieved by in situ synthesis

Abstract

For ceramic reinforced metal matrix composites, it is a critical issue to improve the limited ductility to achieve a combination of high strength and high toughness. Herein, in-situ synthesized MgAlB4 whisker reinforced Al (MgAlB4w/Al) composites with rational distribution of the reinforcement were successfully prepared by an efficient process combining vacuum pressureless sintering and hot-extrusion. The results demonstrate that the MgAlB4 whiskers noticeably coarsen with increasing sintering temperature, while the sintering duration has little effect on the size of the whiskers. The as-extruded composite with 15 wt% MgAlB4w has excellent comprehensive properties with the ultimate tensile strength of 380 MPa and the fracture elongation of ~9.6%. Fracture analysis reveals that the whiskers bear most loads and fracture firstly to form crack sources with the load increasing during drawing. In addition, the alignment distribution of MgAlB4w along extrusion direction is the main reason for the improved ductility of the MgAlB4w/Al composite.