Corrosion behaviour of Mg-xAl-1Si alloys in As-cast and rolled condition through different corrosion test techniques

Magnesium alloy samples of Mg-xAl-1Si alloys with x = 2, 4 and 9 wt% were synthesized using flux less inert gas purging liquid metallurgy route. The cast alloys were also rolled to 90% reduction to a thickness of 2 mm from 20 mm through hot rolling process. The microstructures, XRD, hardness are examined in as-cast and rolled conditions. The Corrosion rate of these materials was examined using three techniques: (i) electrochemical route (Tafel plots), (ii) immersion technique using weight loss measurement, (iii) hydrogen evolution technique through equivalent magnesium loss. The corrosion rates through these three different techniques are compared and it was noted that the corrosion rate measured through electrochemical route and hydrogen evolution technique are in close agreement with each other; but significantly higher than that measured through weight loss (immersion) technique. This demonstrates that the faster technique of electrochemical route could be used successfully for characterizing the corrosion behavior of these alloys. It is further noted that corrosion rate reduced significantly after rolling. It is further noted that alloy with 2 wt% Al exhibited lowest corrosion rate. But this alloy exhibits the lowest strength irrespective of as-cast and rolled condition.