Effect of Nano-SiC on Microstructure and Mechanical Properties of AZ91 Magnesium Alloy Processed by Thixomolding

Abstract

Magnesium injection molding technology was used to produce Mg based nanocomposites. AZ91 chips were mixed with 5 wt.% of β-SiC nanoparticles in solid state and fed to pre-heated cylinder of prototype injection molding machine. Using screw rotation, granules were transferred to nozzle area at simultaneous intensive shearing and mixing of slurry containing reinforcement phases. Injection process was conducted at 595 °C, which corresponded to about 90% liquid phase and cast to steel die preheated to 150 °C. Detailed characterization of microstructure was performed using SEM and TEM microscopes. Composite microstructure consisted of α(Mg) globular grains with size of about 60 μm and volume of 7-10% surrounded by mixture of proeutectic magnesium solid solution with irregular shape and average size of 12 μm as well as fine eutectic mixture (α(Mg) + β-Mg17Al12). Additionally, TEM-BF image showed β-SiC nanoparticles with size of 20-50 nm in the area of eutectic. Hardness and compression strength of AZ91 nanocomposites increased from 58 to 75 HV and from 200 to 235 MPa, respectively.