The corrosion performance of die-cast magnesium alloy MRI230D in 3.5% NaCl solution saturated with Mg(OH)2

The environmental behavior of die-cast magnesium alloy MRI230D designated for high-temperature applications was evaluated in comparison with regular AZ91D alloy. The microstructure examination was carried out using SEM, TEM, and X-ray diffraction analysis; the corrosion performance in 3.5% NaCl solution was evaluated by immersion test, salt spray testing, potentiodynamic polarization analysis, and stress corrosion behavior by Slow Strain Rate Testing (SSRT). Although the general corrosion resistance of MRI230D was slightly improved compared to that of AZ91D alloy its stress corrosion resistance was relatively reduced. The variations in the environmental behavior of the two alloys were mainly due to the differences in their chemical composition and microstructure after die casting. In particular, the differences were related to the reduced Al content in MRI230D and the addition of Ca to this alloy, which consequently affected its relative microstructure and electrochemical characteristics.

Research Highlights
► Corrosion and SCC resistance of a new Mg alloy MRI230D was evaluated vs. regular AZ91D.
► MRI230D has a minor advantage in corrosion performance compared with AZ91D.
► The SCC resistance of MRI230D by SSRT analysis was relatively reduced.
► The reduced SCC resistance of MRI230D was due to the detrimental effect of Ca on ductility.