Influence of Microstructure on the Corrosion Resistance of AZ91D after EB Surface Alloying

This paper focuses on liquid phase surface treatment of the Mg alloy AZ91D by electron beam alloying (EBA) using Al-based additives to improve, primarily, the materials corrosion resistance, as well as its hardness. By variation of EB energy input, layer depths between 0.7 and 2.5 mm were generated. As a result, layers with different Al contents were produced, and were categorized into three different types of microstructure. A correlation could be observed between these three types of microstructure and hardness, as well as between microstructure and corrosion behaviour. Hardness was improved by approximately 2 to 4 times from 67 HV0.1 (base material) up to 140-250 HV0.1 (EBA layer). For high Al contents, the corrosion potential could be increased by about 400 mV compared to the base material. Moreover, it is shown that, after a homogenization process, a corrosion potential of 450 mV above the corrosion potential of the base material was achieved even for low Al contents.