Corrosion mechanism of the as-cast and as-extruded biodegradable Mg-3.0Gd-2.7Zn-0.4Zr-0.1Mn alloys.

Electrochemical measurements and immersion tests were adopted to investigate corrosion mechanism of the as-cast and as-extruded Mg-3.0Gd-2.7Zn-0.4Zr-0.1Mn (GZKM-1) alloys. Results of immersion tests indicate that corrosion resistance of the as-extruded GZKM-1 alloy is better. Galvanic corrosion between α-Mg matrix and β-(MgZn)3Gd compounds is the main corrosion mechanism of the two GZKM-1 alloys. Larger α-Mg peeled off from the as-cast samples, then expanded corrosion reaction along discontinuous β-(MgZn)3Gd compounds making a pit corrosion phenomenon in macro view. Granular β-(MgZn)3Gd or precipitations fell off from the as-extruded samples, and then expanded corrosion reaction along the concentration of the particle β-(MgZn)3Gd (and/or precipitations). Most areas of the as-extruded alloy are protected well by denser protective oxidation film.