Insights into microstructure based corrosion mechanism of high pressure die cast AM50 alloy

Corrosion mechanism of high pressure die cast (HPDC) AM50 magnesium alloy from a planar microstructure context is discussed. The progress of corrosion is mapped by means of electrochemical impedance spectroscopy, microscopy, and by elemental composition distribution analysis. Corrosion resistance of the alloy surface increased on prolonged exposure to the electrolyte (1.6 wt.% NaCl solution), which is attributed to the selective dissolution of Mg-rich alpha phase, and to the evolution of Al-rich surface comprising of Mg17Al12 (beta) and Al-containing eutectic phases. A comparative study between HPDC and sand cast AM50 alloys revealed superior corrosion performance of die cast alloy.

► Experimental evidences provided to proposed theoretical mechanism models in literature. ► Time-lapse EIS on HPDC AM50 revealed an ‘alternating’ trend in corrosion resistances. ► Increased corrosion resistance with time is due to Al enrichment on the surface. ► Corrosion product speciation confirms superior performance of HPDC over SC AM50.