Effect of heat treatment on corrosion and electrochemical behaviour of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Abstract

Corrosion behaviour of Mg–3Nd–0.2Zn–0.4Zr (NZ30K) alloy was investigated in as-cast (F), solution treated (T4) and peak-aged (T6) conditions in 5% NaCl solution by immersion test and electrochemical measurements. The results of immersion test show that the corrosion resistances of NZ30K alloy in three conditions are much higher than that of the commercial AZ91D ingot. NZ30K alloy exhibits better corrosion resistance in T4 temper than it does in the other two conditions due to the dissolution of cathodic compound and higher Nd content in α matrix. Although the corrosion products of NZ30K alloy have different morphologies in three conditions, all of them are compact and uniform. The corrosion product is identified as magnesium hydroxide by XRD. The potentiodynamic polarization curves show that the overpotentials of cathodic hydrogen evolution reaction on NZ30K-T4 and NZ30K-T6 are much higher than on NZ30K-F, and the anodic curves are characterized by clear current plateaus due to the protective corrosion film formed on the surface of the alloy. The results of EIS also confirm that the heat treatment is beneficial to the improvement of the corrosion resistance for NZ30K alloy.