Microstructure evolution and mechanical properties of SiC nanoparticles reinforced magnesium matrix composite processed by cyclic closed-die forging

Magnesium composites containing different amounts of SIC nanoparticles were processed by a two-step cyclic closed-die forging (CCDF), which was carried out at 400 degrees C for 3 passes (lst-CCDF) and further at 300 degrees C for 2 passes (2nd-CCDF). Microstructure evolution and mechanical properties of the composites were investigated. After processing, the average grain size is significantly refined to similar to 2.5 mu m, and the morphology exhibits a flow-lined feature. The beta-Mg17Al12 Phases in the as-cast alloy dissolve completely after lst-CCDF, and then precipitate out with an average size of similar to 650 nm during 2nd-CCDF. After CCDF, the as-cast SiC clusters are uniformly dispersed as separate particles, and the yield strength and ultimate strength of the composites reach 258 MPa and 365 MPa, respectively. The ductility of the composites is enhanced after lst-CCDF but decreased after 2nd-CCDF, which is in accordance with the observed fracture surfaces. From the perspective of strength and ductility, the optimal content of SiC is 0.5 wt%. (C) 2015 Elsevier B.V. All rights reserved.