Influence of Mg3N2 powder on microstructures and mechanical properties of AZ31 Mg alloy

In order to obtain an effective and reliable grain refiner for Mg-Al alloys, 1% (mass fraction) Mg₃N₂ was added into AZ31 Mg alloy. The microstructures of the Mg alloys were studied by optical microscopy, scan electron microscopy and X-ray energy dispersive spectroscopy, and the mechanical properties were determined. The results show that adding a small amount of Mg₃N₂ to AZ31 Mg alloy can refine the grain size from 103 to 58 μm. The ultimate tensile strength and elongation of AZ31 Mg alloy are 174.1MPa and 8.3%, respectively. After the addition of 1% Mg₃N₂, the ultimate tensile strength and elongation of AZ31 Mg alloy are increased up to 198.7 MPa and 11.8%, respectively. The grain refinement mechanism is that AlN is formed after Mg₃N₂ is added. Both AlN and Mg phases are of HCP lattice structure, and the disregistry between Mg phases and AlN along (0001)_Mg//(0001)_AlN is 3.04%, which is very effective for heterogeneous nucleation. Foundation item: Project(2007430023) supported by the Office of Education, Henan Province, China; Project(0612002500) supported by the Excellent Young Scientists Foundation of Henan Province, China