New insights on corrosion behavior of aging precipitates in dilute Mg-Al-Ca alloy by experiments and first-principles calculations

The effects of aging precipitates (i.e. G.P. zone, Al2Ca) on corrosion behavior of Mg-1.0Al-0.3Ca alloy have been systematically investigated combining experiments and first-principles calculations. Being different from Al2Ca causing the micro-galvanic corrosion of Mg matrix, monolayer G.P. zones significantly decrease the corrosion rate (PW) from 11.34 to 6.62 mm/y, and attain excellent corrosion resistance-strength synergy. The G.P. zones composed of Al and Ca atoms corrode preferentially over Mg matrix, resulting in accumulation of more Al-containing corrosion products on alloy surface. Establishment of corrosion product film rich in Al-containing oxides weakens the cathode activity of Mg alloy during corrosion.