Effect of Thermal Exposure on the Corrosion Properties of an Al-Mg-Sc Alloy Sheet

Abstract

The corrosion behaviour of a scandium containing Al-Mg alloy sheet was investigated performing accelerated corrosion tests. The material was studied in an annealed temper (2h at 350°C) and after additional heat treatments at temperatures ranging from 85 to 150°C for time periods up to 3000h. In the annealed condition, the sheet was resistant against intergranular corrosion and stress corrosion cracking and exhibited a moderate susceptibility to exfoliation corrosion. The corrosion resistance was decreased by thermal exposure at temperatures between 85 and 150°C, as indicated by high mass loss and severe exfoliation corrosion attack observed in the NAMLT test and ASSET test, respectively. When alternately immersed in 3.5% NaCI solution under static loading conditions, the scandium bearing Al-Mg alloy was found to be immune against stress corrosion cracking. For sheet material heat treated in the temperature range from 85 to 150°C, environment-induced failure was observed under the severe loading conditions of the slow strain rate testing technique using an aqueous solution of 3% NaCl + 0.3% H 2 O 2 . The deterioration in corrosion resistance of the Al-Mg-Sc alloy sensitised by thermal exposure was associated with grain boundary precipitation of a magnesium rich phase.