The effects of heat treatment and zirconium on the corrosion behaviour of Mg-3Nd-0.2Zn-0.4Zr (wt.%) alloy

The corrosion behaviours of Mg-3Nd-0.2Zn (wt.%) (NZ) and Mg-3Nd-0.2Zn-0.4Zr (wt.%) (NZK) alloys were investigated in as-cast (F), solution-treated (T4) and artificially-aged (T6) conditions in 5% NaCl solution using immersion test and electrochemical measurements. The immersion test indicates that both NZ and NZK alloys exhibit better corrosion resistances in T4 and T6 states than in the F condition due to the galvanic corrosion between the cathodic Mg12Nd compound and the anodic alpha matrix in the F condition. The NZK alloy demonstrates lower corrosion rates than the NZ alloy in three conditions, which indicates that the addition of zirconium has a beneficial effect on the corrosion resistance. It was discovered by field emission scanning electron microscope (FE-SEM) that the corrosion products of NZK-T6 formed in salt solution are composed of sandwich shape compounds, while that of NZ-T6 is composed of fine needle-like compounds and small particles. The former are more uniform and compact than the latter and can play a more protective role for the alloy. Electrochemical measurements also confirmed that the more protective film formed on the NZK than on the NZ alloy. (c) 2006 Elsevier Ltd. All rights reserved.