Effect of bismuth on microstructure, mechanical properties and fracture behavior of AZ magnesium alloys

Magnesium alloys are mostly known for their great availability, superior mechanical properties, and their cost-efficiency compared to other lightweight alloys. Magnesium alloy refinements like Bismuth (Bi) addition can cater the alloy to the needs of industrial units with lower cost and greater mechanical stability in the ambient and elevated temperatures. In current study, the effect of Bi addition (1 and 3 wt%) on microstructure and mechanical properties of the as-cast and solution-treated alloy grades of AZ31, AZ61, and AZ91 were deeply investigated. The volume fraction of the intermetallic phase of Mg3Bi2 directly was related to Bi addition. As a result, homogenous dispersion of Mg3Bi2 particles led to further dispersity of Mg17Al12 particles, which contributed to altering the mechanical properties. Optimum hardness and grain refinement were observed in samples with 1 wt% of Bi. Both the tensile strength and elongation of all alloys improved with the Bi addition. However, for samples with a greater Bi content of 1 wt%, the workability and formability of the alloy decreased. Furthermore, the fracture mechanism of all the samples, regardless of their Bi content, was cleavage and quasi-cleavage, and there was no discernible change in fracture behavior. •A finer dispersion of Mg17Al12 intermetallic phases was observed in the structures as the amount of bismuth in alloys increased.•The homogenization heat treatment dissolved the Mg17Al12 phase in the matrix, but the Mg3Bi2 phase remained dispersed in the structure.•With the Increase of bismuth content, the Mg3Bi2 phase is prone to crushing, which splits the matrix and deteriorates tensile strength and elongation.•Coarse flake phases of Mg3Bi2 act as the initial cracking sites, reducing the ductility of the alloys.