Comparative Evaluation of Corrosion Behavior of Friction Stir Welded AZ61A Magnesium Alloy Weldments in Immersion Corrosion Tests and Salt Spray Corrosion Tests Using Response Surface Methodology

Abstract

Magnesium alloys have gained considerable interest as a material for automotive and aerospace applications due to its low density, high specific strength and good castability. However, an issue is their corrosion properties. This restricts their practical applications. In this work, a comparative evaluation of corrosion behavior of friction stir welded AZ61A magnesium alloy weldments was investigated by immersion and salt spray corrosion tests. Extruded Mg alloy plates of 6 mm thick of AZ61A grade were butt welded using friction stir welding (FSW) process. The specimens were exposed to immersion and salt spray environments in order to characterize their corrosion rates. In addition, an attempt was made to develop an empirical relationship to predict the corrosion rate of the FSW joints in immersion tests and salt spray corrosion tests using response surface methodology. The corrosion morphology and pit morphology observation was carried out by optical microscopy. General corrosion was more prevalent on the immersion surface. However, the pits on the salt spray surface showed larger surface areas, larger volumes, and covered more area on the micrographs as compared to the pits on the immersion surfaces, due to the pit debris that trapped chloride ions within the pits. Finally, it concludes that the FSW AZ61A weldments are suitable for immersion conditions than salt spray environments.