Corrosion behavior of Mg–3Gd–1Zn–0.4Zr alloy with and without stacking faults

To develop biodegradable magnesium alloy with desirable corrosion properties, a low Gd-containing Mg–3Gd–1Zn–0.4Zr (wt%, GZ31K) alloy was prepared. The as-cast ingot was solution treated and then hot extruded. Microstructures were characterized by scanning electron microscopy (SEM). Corrosion behavior of the alloy under each condition was studied by hydrogen evolution and quasi in-situ corrosion methods. It has been found that the as-cast alloy is composed of α-Mg, stacking faults (SFs) at the outer edge of the matrix grains, and eutectic phase along the grain boundaries. After solution treatment, the SFs disappear and precipitates rich in Zn and Zr elements form in the grain interior and boundaries. The microstructure is significantly refined after extrusion. Hydrogen evolution tests show that the as-cast alloy exhibits the best corrosion resistance, and the solution-treated alloy has the worst corrosion resistance. Corrosion rate of the alloy under each condition decreases first and then increases with prolonging immersion time. Corrosion experiments demonstrate that α-Mg was corroded preferentially, the eutectic phase and precipitates exhibit better corrosion resistance. The as-extruded alloy demonstrates uniform corrosion due to fine and homogeneous microstructure.