Effect of fly ash reinforcement on the corrosion behaviour of cast Al-Mg alloy A535 in 3.5 wt% NaCl solution

Abstract

The effect of fly ash reinforcement on the room temperature corrosion behaviour of cast Al-Mg alloy A535 in 3.5 wt pH 7 NaC1 solution was investigated using an immersion corrosion test, electrochemical tests and optical microscopy. The materials studied were A535 and its metal matrix composites (MMCs) containing 10wt fly ash, 15wt fly ash, and a hybrid reinforcement (5wt fly ash5wt SiC). The immersion corrosion test results showed that the corrosion rate of the MMCs increased with increasing fly ash content while the electrochemical test results indicated that their corrosion potential (Ecorr) and critical pitting (breakdown) potential (Ep) decreased with increasing fly ash content. The repassivation potentials of the MMCs were found to be more positive than that of the matrix alloy. The corrosion of the MMCs, which was accompanied by loosening of fly ash particles, was also affected by porosity and the presence of several reaction products.