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

SiC_p reinforced Al-9Si-0.6Mg (wt%) matrix composites were prepared by stirring casting with SiC_p treated by different pre-oxidation time. The effect of a wide range of SiC_p oxidation process on the microstructure and mechanical properties was investigated. The SiC_p/matrix interface layers with different morphology of MgAl₂O₄ were characterized by HAADF-STEM combined with analysis of SiC_p oxidation kinetics. The effect of SiC_p oxidation time on fracture modes and interfacial strengthening mechanisms were studied. The micro-fractures can be classified as primary α-Al cracks, eutectic fractures, SiC_p fractures and interface debonding. 3 h pre-oxidation of SiC_p increases α-Al and SiC_p 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 α-Al and provide more uniform work hardening during the tensile tests. The strengthening effect of MgAl₂O₄ rivets also promote SiC_p to provide a load-bearing capacity with a larger extent and cause the proliferation of stacking faults in SiC_p, further causing SiC_p to crack along the boundary between the stacking-fault zone and the non-stacking-fault zone. However, with the further extension of SiC_p 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 SiC_p, a suitable SiC_p pre-oxidation of 3 h should be introduced into the manufacturing process of SiC_p/Al-Si-Mg composites.