Significant effects of adding trace amounts of Ti on the microstructure and corrosion properties of Mg–6Al–1Zn magnesium alloy

Abstract

Adding trace amounts of Ti (0.01–0.02wt.%) significantly changed the volume fraction, morphology and size of the β phase in the microstructure of as-cast AZ61 alloy, despite its effect on grain size and texture being small, and strongly affected the corrosion properties of the alloy. The addition of 0.01wt.% Ti drastically increased the corrosion rate in sodium chloride solution due to breaking up of the semi-continuous β phase, which destroyed the barrier effect of the β phase against corrosion attack. The addition of a larger amount of Ti (0.02wt.%) also increased the corrosion rate, but the AZ61 alloy with 0.02wt.% Ti exhibited a much better corrosion resistance than the AZ61 alloy with 0.01wt.% Ti. This was because adding 0.02wt.% Ti greatly decreased the volume fraction and size of the β phase, which reduced the galvanic corrosion effect. The current results suggest that a proper control of trace amounts of Ti has a potential to improve the corrosion properties of cast Mg–Al alloys by modifying the microstructure of the β phase.