Effect of 2 wt% calcium addition on the microstructure, mechanical performance, and fracture behaviour of AZ31 magnesium alloy

Abstract This study investigates the effect of 2 wt% calcium (Ca) addition on the microstructure, mechanical properties, and fracture behavior of AZ31 magnesium (Mg) alloy produced via squeeze casting. Ca alloying led to slight reduction in the density from 1.742 to 1.726 g/cm³. Reduction in porosity from 1.58 to 1.37% is also observed due to improved melt wettability and application of squeeze casting. X-ray diffraction confirmed the formation of (Mg, Al)₂Ca intermetallics, while microstructural analysis revealed substantial grain refinement from 93.4 μm to 41.1 μm, attributed to heterogeneous nucleation and solute drag effects. Energy-dispersive spectroscopy indicated Ca and Al segregation at grain boundaries. The refined grains and uniform intermetallic dispersion suppressed twinning, resulting in a 57% hardness increase (106.7 HV), yield strength improvement from 23 MPa to 65 MPa, and ultimate tensile strength enhancement from 121 MPa to 145 MPa. Ductility is found to be reduced from 14% to 8% owing to strain localization near intergranular particles. Fractography indicated a transition from predominantly ductile fracture in base material to a mixed mode in Ca alloyed material. Key results presented in the work highlight the potential of Ca microalloying to enhance the mechanical performance and microstructural stability of AZ31 Mg alloys, offering a promising strategy for lightweight structural applications where mechanical reliability is critical.