Influence of SiC nanoparticles addition on microstructure and creep behavior of squeeze-cast AZ91-Ca-Sb magnesium alloy

The influence of SiC nanoparticles additions on the microstructure and creep behavior of the 2.0Ca + 0.3Sb (wt%) added AZ91 alloy fabricated by squeeze-casting have been investigated. For comparison, the same has also been studied without nanoparticles additions. The α-Mg, β-Mg17Al12, Al2Ca and Ca2Sb phases are present in both the alloy and the nanocomposites. The additions of SiC nanoparticles refined the grain size, reduced the volume fraction of the β-Mg17Al12 phase, and increased the amount of Al2Ca phase, which is more pronounced with an increase in the nanoparticle content. All the nanocomposites exhibit superior creep resistance than the unreinforced 2.0Ca + 0.3Sb (wt%) added AZ91 alloy. The best creep resistance is obtained in the nanocomposite pertaining 2.0SiC (wt%) nanoparticles. The values of stress exponents and the activation energies are in the range of 4.5-6.2, and 101.9 ± 2.5-115.5 ± 3.2 kJ/mol suggesting the governing creep mechanism for the alloy and the nanocomposites is dislocation climb controlled by pipe diffusion. The post creep microstructural observation confirms that the β-Mg17Al12 phase in the alloy is rigorously fragmented, and aligns in the direction of material flow, which deteriorates its creep resistance. In contrast, the presence of Al2Ca phase network and the SiC nanoparticles increase the dislocation pile-ups and dislocation tangling resulting in superior creep resistance of all the nanocomposites.