The effect of Ca and rare earth elements on the microstructure, mechanical properties and corrosion behavior of AZ91D

The microstructure, mechanical properties and corrosion behavior of AZ91 with addition of Ca and rare earth elements (REs) were investigated using tensile tests, X-ray diffraction, SEM, EDX, immersion tests and electrochemical polarization experiments. The addition of 1%Ca led to the formation of reticular Al2Ca phase, which improved the corrosion resistance of AZ91D alloys. The reticular Al2Ca phase had a detrimental influence on the mechanical properties of AZ91 alloys; however, the addition of REs improved the ultimate tensile strength of the AZ91 alloy, but the corrosion resistance increased slightly compared with the addition of Ca. With the addition of 1%Ca and 1%REs to AZ91, the ultimate tensile strength increased by 15.9% and the corrosion rate decreased to 0.086 mg cm−2 day−1 due to the formation of the reticular Al2Ca phase, which acted as an effective barrier against corrosion.