Implants are inevitably subjected to stress corrosion, bringing serious challenges to the controlled degradation of biomedical Mg alloys. It is worth studying the stress corrosion cracking (SCC) behavior of Mg alloy and exploring Mg alloy with good SCC resistance for wide biomedical applications. In this work, the as-cast and as-extruded Mg-3Gd-1Zn-0.4Zr (GZ31K) alloys with uniform corrosion were used to investigate SCC behavior. The as-extruded GZ31K alloy exhibited better corrosion resistance and mechanical properties than the as-cast one mainly owing to grain refinement and uniformly distributed fine precipitates, and possessed superior SCC resistance. To clarify the SCC mechanism, the slow strain rate tests were assisted with applied constant potentials via an electrochemical workstation. Accelerated anodic dissolution at anodic polarization deteriorated SCC resistance due to the initiation of corrosion pits and micro-cracks. However, cathodic polarization had no obvious effects on SCC resistance, along with both retarded corrosion and accelerated hydrogen evolution. Stacking faults in GZ31K alloy were hydrogen capture containers to reduce the effect of hydrogen on SCC resistance during cathodic polarization. These findings provide new insights into the evaluation of SCC mechanism, and offer more opportunities to explore Mg alloys with good SCC resistance by regulating anodic dissolution.

Magnesium (Mg) alloys have been widely used in automobile, aviation, computer, and other fields due to their lightweight, high specific strength and stiffness, low pollution, and good electromagnetic shielding performance. However, the chemical stability of Mg alloys is poor, especially in the corrosive medium environment with high stress corrosion sensitivity, which causes sudden damage to structural components and restricts their application field. In recent years, owing to the increasing failure rate of engineering structures caused by stress corrosion of Mg alloys, it has become necessary to understand and pay more attention to the stress corrosion cracking (SCC) behavior of Mg alloys. In this paper, the SCC mechanisms and test methods of Mg alloys have been summarized. The recent research progress on SCC of Mg alloys has been reviewed from the aspects of alloying, preparation process, surface modification, corrosive medium, and strain rate. More importantly, future research trends in the field of SCC of Mg alloys have also been proposed.