Improvement in impression creep property of as-cast AC515 Mg alloy by Mn addition

The effect of Mn on the impression creep behavior and microstructure of AC515 (Mg-5Al-1.5Ca) alloy has been studied. Four alloys based on AC515 with different Mn contents 0, 0.3, 0.5 and 0.8 wt% were prepared. The study showed that the impression creep properties of AC515 alloy are significantly improved by Mn addition. Addition of Mn up to 0.5 wt% increases the impression creep resistance, whereas incorporation of 0.8 wt% Mn decreases the impression creep resistance of samples. The microstructure of AC515 alloy consists of (Mg,Al)2Ca distributing in the α-Mg matrix. Addition of Mn causes formation of Al8Mn5 in matrix and interdendritic regions. The stress exponent and activation energy are in the ranges of 5-6 and 97.3-99 kJ/mol, respectively, for all alloys. The suggested creep mechanism under the experimental conditions is pipe diffusion dislocation climb.