Role of Sn in microstructure and corrosion behavior of new wrought Mg-5Al alloy

Abstract

The effect of Sn additions on the microstructure and corrosion behavior of new wrought Mg-5Al-xSn (x = 0.71, 1.47, 2.44, and 3.09 wt%) was studied through optical and electron microscopy, XRD, hydrogen evolution test, and electrochemical measurements. Increasing of the Sn content was followed an increase in the quantity of Sn dissolved in the Mg matrix and precipitation of Mg2Sn intermetallics when Sn content exceeded 1.47 wt%. The corrosion mode in a short immersion period was pitting corrosion; presence of cathodic sites (i.e., Mg2Sn intermetallics) deteriorated the alloys' corrosion resistance. However, with a long immersion period the corrosion mode of the alloys with Sn content above 0.71 wt% was mixed pitting and filiform corrosion, indicating that a passivation layer was formed on the alloys' surface and increased their corrosion resistance.