Corrosion behaviour in salt spray and in 3.5% NaCl solution saturated with Mg(OH)2 of as-cast and solution heat-treated binary Mg–RE alloys: RE=Ce, La, Nd, Y, Gd

Abstract

Abstract Corrosion behaviour was characterised in salt spray and in 3.5% NaCl solution saturated with Mg(OH)2 of as-cast and solution heat-treated binary Mg–RE alloys. The corrosion rate in the immersion test for the solution heat-treated Mg–RE alloys was substantial, and was greater than that of high-purity Mg. These corrosion rates were probably caused by the particles in the microstructure and/or by Fe rich particles precipitated during the solution heat-treatment. The corrosion rate in the immersion tests for each as-cast Mg–RE alloy was greater than that of high-purity Mg, attributed to micro-galvanic acceleration caused by the second phase. Corrosion rates in salt spray had a general correlation with corrosion rates in the immersion tests, but there were differences. The values of apparent valence were always less than 2 consistent with Mg corrosion being only partly under electrochemical control.