Microstructure evolution and assessment of creep behaviour of SiC nanoparticles dispersed squeeze-cast Mg-5.0Al-2.0Ca-0.3Mn alloy

The microstructural modification and creep behaviour of Mg-5.0Al-2.0Ca-0.3Mn (AXM520) alloy with SiC nanoparticles (SiCnp) dispersion have been investigated. The concentrations of the SiCnp are varied from 0.5 to 3.0 (wt.%), and the squeeze-cast nanocomposites (NCs) are abbreviated as NC0.5SiC, NC1.0SiC, NC2.0SiC and NC3.0SiC. The microstructures of the AXM520 alloy and NCs consist of a primary solid solution (alpha-Mg), a eutectic of alpha-Mg and (Mg,Al)2Ca (C36), and an Al8Mn5 phase. Additionally, the SiC phase is also present in the NCs. The continuous network of the C36 phase in the NCs is fragmented and becomes discontinuous with the increase in the fraction of the SiCnp. All the NCs revealed improved creep performance compared to the AXM520 alloy. The creep rate of the NCs decreases with the increase in the SiCnp content. The NC2.0SiC exhibited an improvement in creep resistance by 73.2 % compared to the alloy. However, the creep resistance deteriorated since the amount of the nanoparticles was further increased in the NC3.0SiC, leading to agglomeration. The stress exponents vary from 5.0 to 6.7, and activation energies vary from 89.8 to 101.8 kJ/mol, implying that the creep in the materials is controlled by the climb of dislocation assisted by the pipe diffusion. The pile-ups of dislocations took place around the C36 phase and near the SiCnp. The additional strengthening owing to the presence of the SiCnp in the NCs was responsible for their improved creep performance compared to the AXM520 alloy.