The effect of Sr addition on the microstructure and corrosion behaviour of a Mg-Zn-Ca alloy

The application of magnesium alloys is rather limited due to their poor corrosion resistance despite of their promising mechanical properties. Alloying is considered one of the most efficient methods to influence the corrosion susceptibility of Mg alloys either by altering the bulk microstructures or by changing the surface chemistries. In the present study, the effects of Sr addition on the microstructure and corrosion properties of a Mg-Zn-Ca alloy were studied. The microstructure characteristics of the alloys were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, while the corrosion properties were evaluated by hydrogen collection method and electrochemical techniques including potentiodynamic polarization and electrochemical impedance spectroscopy. The results indicate that Sr addition significantly deteriorates the corrosion performance of the Mg-Zn-Ca alloy mainly by forming more micro-galvanic couples due to the precipitation of the more populous secondary phase particles. The corrosion prod-uct film accumulated on the sample surface marginally affects the corrosion resistance, as their compactness is rather compromised as the immersion time is prolonged.