Effect of misch metal on the corrosion behaviour of AZ91 magnesium alloysunder wet-dry circles

Abstract:

The microstructure and element distribution of AZ91 alloy have been changed by adding the mischmetal of lanthanum and cerium (La, Ce). The existence forms of La and Ce elements in AZ91 alloy are different. Part of them can be dissolved in the α-Mg solid solution, the others formed the different intermetallic compounds with a chemical composition Al₄(La,Ce)or Al₁₀Ce₂Mn₇, Al₄(La,Ce)is in acicular shape and Al₁₀Ce₂Mn₇ is in granular shape. The fraction of β phase in AZ91 alloy decreased obviously with the addition of misch, and the distribution of Al element transferred from the grain boundaries to grain internal area. The study results on the corrosion behavior of AZ91 magnesium alloys with addition of misch in de-icy solution under wet-dry circles showed that a shift of the corrosion potential (Ecorr) towards more negative values is observed for all the alloys with misch addition, but their corrosion current densities (Icorr) are much lower compared to that of the AZ91 alloy. The scanning electrochemical microscopy (SECM)test results revealed that the addition of could reduce the number of electrochemical active points on the surface. In addition, the compactness of corrosion product film of magnesium alloy was increased with addition of misch.