Effects of SiC oxide morphology on bearing capacity of SiC and mechanical properties of SiCp/Al-Si-Mg composites

SiCp reinforced Al-9Si-0.6Mg (wt%) matrix composites were prepared by stirring casting with SiCp treated by different pre-oxidation time. The effect of a wide range of SiCp oxidation process on the microstructure and mechanical properties was investigated. The SiCp/matrix interface layers with different morphology of MgAl2O4 were characterized by HAADF-STEM combined with analysis of SiCp oxidation kinetics. The effect of SiCp oxidation time on fracture modes and interfacial strengthening mechanisms were studied. The micro-fractures can be classified as primary alpha-Al cracks, eutectic fractures, SiCp fractures and interface debonding. 3 h pre- oxidation of SiCp increases alpha-Al and SiCp fractures significantly while the interface debonding decreases, and shows the best improvement on strength and plasticity. The improvement mechanism can be attributed to the strengthening effect of MgAl2O4 rivets on the interface, which lead to stronger plastic deformation in the primary alpha-Al and provide more uniform work hardening during the tensile tests. The strengthening effect of MgAl2O4 rivets also promote SiCp to provide a load-bearing capacity with a larger extent and cause the proliferation of stacking faults in SiCp, further causing SiCp to crack along the boundary between the stacking-fault zone and the non-stacking-fault zone. However, with the further extension of SiCp oxidation, mixed interface products layers consisted of MgAl2O4 polycrystalline layer, silicon and non-crystalline SiO2 tend to be formed to deteriorate the mechanical properties of composites. Therefore, in order to exploit the load-bearing capacity from SiCp, a suitable SiCp pre-oxidation of 3 h should be introduced into the manufacturing process of SiCp/Al-Si-Mg composites.