Comparison of Corrosion Properties of Squeeze Cast and Thixocast MgZnRE Alloys

Abstract

Thixocasting is a new semi-solid processing route for magnesium castings. However it is claimed that finer microstructures can be produced and as a consequence a better corrosion resistance is obtained. Therefore it is of great interest to compare the corrosion properties of two Mg-Zn-RE alloys produced by standard squeeze casting and new semi-solid casting technique. The influence of the two different processing routes and the replacement of RE elements by Ca additions on the corrosion behaviour were studied in 3.5% NaCl and ASTM Water by (a) analysing the corrosion morphology, (b) measuring electrochemical polarization curves and (c) immersion tests at constant pH-Value. By using LM, SEM and XRD to evaluate the microstructure before and after the corrosion measurements, the corrosion results will be related to the microstructures of the specific alloys. The results indicate that Ca can not replace RE elements under corrosion aspects, but they also show that the thixocasting process indeed results in better corrosion resistance.