Magnesium alloys are attractive for the production of lightweight parts in modern automobile and aerospace industries due to their advanced properties. Their mechanical properties are usually enhanced by the incorporation with reinforcement particles. In the current study, reinforced AZ31 magnesium alloy was fabricated through the addition of bulk Al and the incorporation of SiC nanoparticles using a stir casting process to obtain AZ31-SiC nanocomposites. Scanning electron microscope (SEM) investigations revealed the formation of Mg₁₇Al₁₂ lamellar intermetallic structures and SiC clusters in the nanocomposites. Energy dispersive spectroscopy (EDS) detected the uniform distribution of SiC nanoparticles in the AZ31-SiC nanocomposites. Enhancements in hardness and yield strength (YS) were detected in the fabricated nanocomposites. This behavior was referred to a joint strengthening mechanisms which showed matrix-reinforcement coefficient of thermal expansion (CTE) and elastic modulus mismatches, Orowan strengthening, and load transfer mechanism. The mechanical properties and wear resistance were gradually increased with an increase in SiC content in the nanocomposite. The maximum values were obtained from nanocomposites containing 1 wt% of SiC (AZ31-1SiC). AZ31-1SiC nanocomposite YS and hardness were improved by 27% and 30%, respectively, compared to AZ31 alloy. This nanocomposite also exhibited the highest wear resistance; its wear mass loss and depth of the worn surface decreased by 26% and 15%, respectively, compared to AZ31 alloy.

In this study, the AZ31 magnesium alloy was reinforced with tungsten disulfide (WS₂) nanotubes to fabricate the nanocomposite using the stir casting method. The microstructural analysis, mechanical and wear behaviors were investigated with the effect of WS₂ on the AZ31 alloy. Scanning electron microscopy (SEM) was used to conduct the microstructural analysis. The microstructures are revealed to incorporate the aluminum content with the WS₂ nanotube, disclose the presence of the secondary phase, which was increased compared with the AZ31 alloy and was detected by energy dispersive spectroscopy (EDS). The mechanical properties of hardness and yield strength (YS) were significantly improved with the addition of WS₂ nanotubes. This is mainly due to the strengthening mechanisms of Orowan, the coefficient of thermal expansion (CTE) mismatch and the load transfer mechanism. The theoretical YS was calculated and compared with the experimental results. However, the ultimate tensile strength (UTS) and the fracture strain were decreased with the addition of reinforcement which might be owing to the clustering of nanotubes. Finally, the wear behavior of the wear weight loss and depth of cut was investigated. This test revealed that the addition of WS₂ nanotubes reduced the weight loss and depth of the material cutting that was mainly due to the presence of hard WS₂ nanotubes.

Gravitational melt-stir casting produced hybrid nano-reinforcements (β-SiCp) and micro-reinforcements (Bi and Sb) of AZ91 composites. SiCp-diffused discontinuous β-Mg₁₇Al₁₂ precipitation with a vital factor of SiC was exhibited at the grain boundary region, formulated Mg₃Si throughout the composite and changed the present Mg_0.97Zn_0.03 phases. The creation of Mg₂Si (cubic) and SiC (rhombohedral axes) enhanced the microhardness by 18.60% in a 0.5 wt.% SiCp/AZ91 matrix. The microhardness of 1 wt.% SiCp/AZ91 was slightly reduced after Mg_0.97Zn_0.03 (hexagonal) reduction. The best ultimate tensile value obtained was about 169.33 MPa (increased by 40.10%) in a 0.5 wt.% SiCp/AZ91 matrix. Microelements Bi and Sb developed Mg₃Bi₂, Mg₃Sb₂ and monoclinic C₆₀ phases. The best peak yield strength of 82.75 MPa (increased by 19.85%) was obtained with the addition of 0.5 wt.% SiCp/1 wt.% Bi/0.4 wt.% Sb. The mismatch of the coefficient of thermal expansion of segregated particles and the AZ91 matrix, the shear transfer effect and the Orowan effect, combined with the quantitative value of phase existence, improved the compressive strengths of the composites with 0.5 wt.% β-SiCp, 1 wt.% β-SiCp and 0.5 wt.% SiCp/1 wt.% Bi/0.4 wt.% Sb by 2.68%, 6.23% and 8.38%, respectively. Notably, the Charpy impact strengths of 0.5 wt.% and 1 wt.% β-SiCp-added AZ91 composites were enhanced by 236% (2.89 J) and 192% (2.35 J), respectively. The addition of Bi and Sb with SiCp resulted in the formation of a massive phase of brittle Al₆Mn. Al–Mn-based phases (developed huge voids and cavities) remarkably reduced impact values by 80% (0.98 J). The discussion covers the quantitative analyses of X-ray diffraction, optical microscopy and scanning electron microscopy results and fracture surfaces.