Abstract

Alx(Mn,Fe)y phase, as a common derivative of Fe-containing impurities, significantly deteriorates the protectiveness of phosphate conversion coatings (PCC) on magnesium alloys due to the micro-galvanic effect. This work presents a novel pretreatment method, aiming at chemically depleting the noble Alx(Mn,Fe)y phase from Mg alloy surface before PCC treatment. The pretreatment bath contains both oxidant and complexing agent, with the pH value and concentration of different constituents being determined by thermodynamic calculation. The corrosion resistance of PCC being preceded by exploiting the novel pretreatment method was improved, which was attributed to the mitigation of micro-galvanic corrosion.

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