Impression Creep and Corrosion Behaviour of MRI230D Magnesium Alloy

Abstract

Impression creep and corrosion behaviour of the MRI230D alloy have been investigated. The impression creep experiments are carried out in the temperature range 150-225oC and stress range 225-325 MPa by impressing a cylindrical indenter on the surface of specimen. Microstructure of MRI230D consists of α-Mg phase, (Mg,Al)2Ca (C36) phase and few Al-Mn-rich phase. All the creep plots exhibit a well-defined primary creep followed by secondary (steady state) creep. Tertiary stage is missing in all the plots owing to the compressive nature of the tests. The values of stress exponent (n) vary from 5.0 to 5.4 and the values of activation energy (Q) vary from 75 to 85 kJ/mol, which confirms dislocation climb controlled by pipe diffusion is the dominant creep mechanism in the MRI230D alloy in the temperature and stress levels employed. The results of XRD and microstructural observation of the as-cast and creep tested specimens conclude that the superior creep resistance of the MRI230D alloy due to the presence of the thermally stable C36 phase along grain boundaries. Electrochemical corrosion tests at 5% NaCl with pH 11 are carried out on the MRI230D alloy and results are compared with that of AZ91 alloy. The MRI230D alloy exhibits better corrosion resistance owing to the absence of Mg17Al12 phase in it.