Processing and mechanical properties of in-situ magnesium matrix composites containing nano-sized polymer derived sicno particles

Abstract

In-situ magnesium metal matrix composites seem to be gaining attraction in next generation light weight vehicular applications since it overcomes several issues (non-uniformity of particle distribution, poor wettability and weak interfaces) associated with conventional MMCs. We introduced liquid polymer directly into the molten magnesium at 700 oC and then having it converted into 2.5 vol% SiCNO particles (mean particle size in the range of 0.5-1 m) using a stir-casting method. Majority of the polymer derived SiCNO particles were pushed by the solidification front and as a result segregated at the grain boundaries (mean grain size in range of 50-65 m) of in-situ composites during solidification. Therefore, the as-cast magnesium composite is subjected to single pass friction stir processing technique in order to improve the uniformity of SiCNO particle dispersion, refinement of reinforced particles (mean particle size of about 200-300 nm), and grain size (mean grain size in range of 2.5-3.5 m) along with its mechanical properties. An enhancement of hardness, yield strength, strain to failure and strain hardening exponent in two-stage processed composites is discussed on the basis of microstructural evolution, and strengthening mechanisms.