Effects of Si addition on microstructure and mechanical properties of RS/PM (rapid solidification and powder metallurgy) AZ91 alloy

AZ91 alloy powder with 2 mass% Si addition (flakes) was obtained by two-roller quenching equipment with an atomized accessory. The powders were consolidated and extruded into bar. The microstructures of the powders (flakes) and bars were characterized by optical microscope (OM), XRD, TEM and SEM. The results showed that the grain size of the powder were dendritic with the sizes of about 1–5 μm. The as-extruded alloy bars retain equiaxed grains with a large number of precipitated phases, i.e. Mg2Si, β-Al12Mg17 and AlMg2Zn. The alloy exhibits excellent mechanical properties. The 0.2% yield tensile strength, ultimate tensile strength and elongation of rupture were 322.47, 429.78 MPa and 6.4%, respectively. The as-extruded alloy bars show preferable elevated temperature mechanical properties.