Influence of hybrid reinforcements on the mechanical properties and morphology of AZ91 magnesium alloy composites synthesized by ultrasonic-assisted stir casting

In the present study, AZ91 magnesium alloys reinforced with a fixed weight fraction of aluminium oxide (Al2O3: 1.5 wt%) and titanium di-boride (TiB2: 1, 3, and 5 wt%) particle hybrid metal matrix composites were developed using the stir casting method assisted with ultrasonic agitations. The microstructural analysis reveals that the structure of monolithic alloy is made up of & alpha;-Mg grains with evenly distributed & beta;-Mg17Al12 intermetallic secondary phases near the grain boundaries. Incorporating hybrid reinforcements into the matrix alloy decreases the average grain size and also leads to the breakdown of the & beta;-Mg17Al12 phase from a rounded shape to sharp needle-like profiles. The micro-hardness, ultimate tensile strength, and impact strength outcomes revealed a direct correlation with varying TiB2 particulate contents, the peak values of which have been achieved with the addition of 3 wt% of TiB2 particulates with AZ91 + 1.5 wt% Al2O3 hybrid composite.

Automated summary

In this study, AZ91 magnesium alloys reinforced with hybrid metallic matrix composites consisting of a fixed weight fraction of aluminium oxide (Al2O3: 1.5 wt%) and varying amounts of titanium di-boride (TiB2: 1, 3, and 5 wt%) particles were developed using the stir casting method assisted with ultrasonic agitations. The analysis of the microstructure showed that the monolithic alloy consisted of α-Mg grains with evenly distributed β-Mg17Al12 intermetallic secondary phases near the grain boundaries. Incorporating hybrid reinforcements into the matrix alloy resulted in a decrease in average grain size and a transformation of the β-Mg17Al12 phase from rounded to needle-like profiles. The study of micro-hardness, ultimate tensile strength, and impact strength revealed that the addition of 3 wt% of TiB2 particulates in the AZ91 + 1.5 wt% Al2O3 hybrid composite achieved the highest peak values.