Purpose This paper aims to investigate the corrosion evolution process of AZ91 magnesium alloy in 3.5 wt.% NaCl solution under different stresses by using in situ methods, thereby evaluate the influence of stress on the corrosion sensitivity of AZ91 magnesium alloy, and discuss the potential mechanism. Design/methodology/approach A four-point bending method was used to apply different loads to the magnesium alloy samples, a charge coupled device camera and electrochemical impedance spectroscopy test being used for in situ study. Scanning electron microscopy and X-ray diffraction (XRD) analysis were performed for corrosion product and morphology characteristics. Findings The observation results show that the corrosion of AZ91 magnesium alloy becomes more and more serious with the increase in the stress and generated many corrosion products. Originally, corrosion products prevented alloy matrix from contacting the corrosive medium. However, the increase in the stress facilitated the emergence of the corrosion holes in the corrosion products, which provided the microscopic channels for corrosive solution to attack the Mg alloy matrix, and accelerated the corrosion of the magnesium alloy, resulting in a lot of corrosion pits on the magnesium alloy surface under the corrosion product layer. Originality/value The evolution information of corrosion process is crucial to explore the mechanism of corrosion. Currently, most researches about corrosion of magnesium alloy used traditional testing techniques to obtain corrosion information, lacking the direct tracking and monitoring of the corrosion evolution process. Hence, this paper focuses on in situ corrosion study of AZ91 magnesium alloy. The technology with spatial resolution capability observed the changes in magnesium alloy surface at different times in the corrosion process in situ. Meanwhile, the in situ electrochemical technology was used to monitor the changes in micro-electrochemical signals during the corrosion process of magnesium alloy under different stresses.

The corrosion behavior of X80 steel in a near-neutral soil-simulated solution under various DC stray currents and applied strains was investigated using electrochemical measurements (open circuit potential, linear polarization, and electrochemical impedance spectroscopy) and surface analysis techniques. Our results show that a DC stray current has a substantially greater effect on steel corrosion compared to applied strain. However, strain could slow down the corrosion rate in specific conditions by affecting the composition of corrosion products and the structure of the corrosion scale on the surface of the steel. Although the porosity of the corrosion scale of steel without an applied strain will increase with increasing DC currents, once strain is applied, the corrosion scale will become denser. Furthermore, both DC currents and strain can promote steel pitting, and the number and size of pitting holes will increase significantly with an increase in current densities.