Corrosion products of field-exposed Mg-Al series magnesium alloys

Corrosion products on hot-extruded AZ31B, AM60, AMX602 and AZ91D alloys exposed in actual atmospheric environments for 3 years were examined, and the surface appearance and corrosion resistance of the field-exposed magnesium alloys were investigated. It was found that layered double hydroxide (Mg0.833Al0.167)(OH)2(CO3)0.083·0.75H2O formed on all alloys at early stages of exposure, and the corrosion products after 3-year exposure were associated with Al content in magnesium alloy matrix. Corrosion-product layer morphology had a great influence on the corrosion resistance and surface appearance of the magnesium alloys. The relation between corrosion-product layer thickness and corrosion depth was also discussed.