Microstructure characteristics and enhanced tensile properties of in-situ AlN/ AZ91 composites prepared by liquid nitriding method

Nano-, submicron- and micron-sized AlN particles were in situ synthesized in AZ91 matrix alloy by liquid nitriding method. According to thermodynamics calculation and experimental results, the nitriding reactions of AlN particle formation were stably completed in the matrix AZ91 alloy melt. And in situ formed AlN particles with the granular and rod-like shapes were uniformly distributed in the matrix. Thus, the grain sizes of α-Mg were significantly refined, the amount and sizes of β-Mg17Al12 phases were decreased, and a lot of dislocations trapping and the precipitation of γ-Mg17Al12 phase were induced in the AZ91 matrix alloy. As results, higher ultimate tensile strength (240 ± 10 MPa) and higher fracture elongation (20 ± 3%) were simultaneously improved for AlN/AZ91 permanent mold casting composites.