Corrosion Resistance of Mg/Al Vacuum Diffusion Layers

This study used a vacuum diffusion welding process to weld magnesium (Mg1) and aluminum (Al1060). The diffusion layers, with different phase compositions, were separated and extracted by grinding. The diffusion layers’ microstructures and phase compositions were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Furthermore, the corrosion resistance of each diffusion layer and the substrates were investigated and compared by performing corrosion immersion tests and linear polarization measurements in a 3.5 wt.% NaCl solution. The results showed that diffusion layers consisting of Mg2Al3, Mg17Al12, and Mg17Al12/Mg-based solid solutions were formed at the interface of the Mg1/Al1060 vacuum diffusion joint. Furthermore, each diffusion layer’s structure and morphology were of good quality, and the surfaces were free from defects. This result was obtained for a welding temperature of 440 °C and a holding time of 180 min. The corrosion current density of Mg1 was 2.199 × 10−3 A/cm2, while that of the Al1060, Mg2Al3, Mg17Al12, and Mg17Al12/Mg-based solid solutions increased by order of magnitude, reaching 1.483 × 10−4 A/cm2, 1.419 × 10−4 A/cm2, 1.346 × 10−4 A/cm2, and 3.320 × 10−4 A/cm2, respectively. The order of corrosion rate was Mg1 > Mg17Al12 and Mg-based solid solution > Mg2Al3 > Mg17Al12 > Al1060. Moreover, all diffusion layers exhibited an improved corrosion resistance compared to Mg1. This was especially the situation for the Mg2Al3 layer and Mg17Al12 layer, whose corrosion resistances were comparable to that of Al1060.