Effect of Mg addition on the microstructure and mechanical properties of SiC nanowires reinforced 6061Al matrix composite

The precipitation sequence of 6061Al has changed after introducing high amount SiC nanowires due to the serious segregation of Mg element. In the present work, 0.8 wt% Mg element was added into 6061Al matrix to compensate the segregation effect, and the 15 vol% SiCnw/6061Al+0.8Mg composite was prepared by pressure infiltration method. Regardless of aging time, the hardness of SiCnw/6061Al composite could be improved by the addition of Mg. MgAl2O4 phase at SiC nanowire-Al matrix interface was found in SiCnw/6061Al+0.8Mg composite after solid solution treatment. The ultimate precipitate of Al matrix in SiCnw/6061Al+0.8Mg composite has been restored from B′ (MgSi>1) to β (Mg2Si). Moreover, the hardness of composites was improved 10% after addition of Mg in the over-aging status, implying that the strengthening effect of B′ phase might be inferior to that of β' and β phases. Due to early failure behavior, the tensile strength of the peak-aged composites was slightly decreased by the addition of Mg element. However, the yield strength of the composites was improved, which could be well explained by the modified shear-lag model. It is suggested that addition of extra alloying elements to compensate the segregation effect might be an effect method to improve the yield strength. However, for the application favor high tensile strength, design of performance matching in elastic-plastic behavior between matrix and reinforcement and the ability of Al matrix to relax the stress concentration might be the advisable choice.