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

Adding trace amounts of Ti (0.01-0.02 wt.%) significantly changed the volume fraction, morphology and size of the beta 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 0.01 wt.% Ti drastically increased the corrosion rate in sodium chloride solution due to breaking up of the semi-continuous beta phase, which destroyed the barrier effect of the beta phase against corrosion attack. The addition of a larger amount of Ti (0.02 wt.%) also increased the corrosion rate, but the AZ61 alloy with 0.02 wt.% Ti exhibited a much better corrosion resistance than the AZ61 alloy with 0.01 wt.% Ti. This was because adding 0.02 wt.% Ti greatly decreased the volume fraction and size of the beta 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 beta phase. (C) 2014 Elsevier B.V. All rights reserved.