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.

Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance. The reliable monitor should be high distinguishability and real-time in liquid environment. Herein, Mg-9Al-1Fe and Mg-9Al-1Fe-1Gd alloys were designed to highlight the impact of intermetallic on the corrosion behaviour. In-situ AFM with a special electrolyte circulation system and quasi-in-situ SEM observation were used to monitor the corrosion process of the designed alloys. SEM-EDS and TEM-SAED were applied to identify the intermetallic in the designed alloys, and their volta potentials were measured by SKPFM. According to the real-time and real-space in-situ AFM monitor, the corrosion process consisted of dissolution of anodic α-Mg phase, accumulation of corrosion products around cathodic phase and shedding of some fine cathodic phase. Then, the localized corrosion process of Mg alloy was revealed combined with the results of the monitor of corrosion process and Volta potential difference.

The corrosion inhibition behavior of Mg-8Li-3Al alloy in NaCl solution with sodium dodecyl sulfate (SDS) was investigated by hydrogen analysis, scanning electron microscopy (SEM), electrochemical test, scanning Kelvin probe force microscopy (SKPFM) and computational methods. Results showed that the corrosion resistance of Mg-8Li-3Al alloy in NaCl solution was effectively improved with SDS. The SEM and SKPFM results confirmed a dense, 200 nm-thick SDS-adsorbed layer had formed on the alloy surface. The separation energy ∆E_gap and adsorption energy E_ads of SDS on the Mg surface were calculated by density functional theory and molecular dynamics simulations, respectively. And the corrosion inhibition mechanism was hypothesized and described.