Ying Xiong

AZ80 magnesium alloy was surface treated by micro‐arc oxidation (MAO) and composite of laser shock penning (LSP) and MAO techniques. Untreated and treated specimens were pre‐corroded in simulated body fluids (SBF) with different pH values (pH 4, 7.4, and 9). The ratcheting behavior of all test specimens was experimentally investigated under stress‐controlled loading. The positive or negative value of the ratcheting strain reflects the mechanism of cyclic deformation. The ratcheting strain with negative values is associated with the cyclic deformation being dominated by twinning–detwinning, while the ratcheting strain with positive values is due to dislocation slip playing a dominant role in the cyclic deformation. A higher absolute value of the ratcheting strain means a lower the ratcheting life. Single MAO coating is not conducive to the fatigue life of magnesium alloy in acidic SBF environment, while LSP/MAO composite coating can improve the fatigue life of magnesium alloy under various loading conditions and different pH environment.

Slow strain rate tensile (SSRT) testing was performed on AZ80 magnesium alloy plate along different orientation at a nominal stain rate, viz., 1 × 10⁻⁶/s and 5.3 × 10⁻⁷/s, in a simulated body fluid (SBF). Two types of orientation specimens were machined from the rolled plate with the loading axes of testing specimens along 0° (RD) and 30° (RD30) with respect to the rolled direction. The stress corrosion cracking (SCC) behavior of specimens with different orientation was studied by a combination of electrochemical impedance spectroscopy (EIS) and SSRT analysis. The fracture surface of the specimens was observed by scanning electron microscope (SEM). The initiation and propagation of cracking are analyzed by the EIS information recorded during the SSRT loading. Based on the experimental observations, the stress corrosion mechanism of AZ80 Mg alloy with different initial texture was revealed.

A laser shock peening (LSP) layer, a micro-arc oxidation (MAO) coating, and an LSP/MAO composite coating were fabricated on the surface of AZ80 magnesium alloy by laser shock and micro-arc oxidation process. The ball-disc grinding method was used to perform wear test on the three treated specimens in simulated body fluids (SBF) with pH values of 4, 7.4 and 9. The morphology and element content of worn surface were investigated by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results indicated that the wear rates of the three treated specimens in three pH environment in numerical order were pH 4 > pH 7.4 > pH 9, respectively. The wear rates of the three treated specimens in the same pH environment were arranged in the order of MAO > LSP > LSP/MAO, respectively. The main wear mechanisms of the LSP specimen in pH 4 environment were fatigue wear and corrosion wear, while it were corrosion wear and adhesive wear in pH 7.4 and pH 9 environments. Abrasive wear, fatigue wear and corrosion wear were the main wear mechanisms of the MAO specimen in pH 4 environment, while abrasive wear, adhesive wear and corrosion wear were the main wear mechanisms of that in pH 7.4 and pH 9 environments. The corrosion wear resistance of the LSP/MAO specimen in SBF solution with three pH values was improved due to the synergism of LSP fine crystal layer and MAO coating.

A bio‐ceramic coating was prepared on the surface of ZK60 magnesium alloys by micro‐arc oxidation (MAO) method. The substrate (BM) and coated (MAO) specimens were pre‐corroded in a simulated body fluid (SBF) for 12 h. Strain‐controlled and stress‐controlled loading modes were used to conduct fatigue tests for the specimens with non‐corroded and pre‐corroded, and the cyclic deformation behavior of different specimens was studied. The fatigue life of pre‐corroded MAO specimen is higher than that of pre‐corroded BM specimen. The mechanism of cyclic deformation under different loading conditions is related to twinning and slip. For the same specimens, the higher the absolute value of ratcheting strain, the lower the fatigue life. A modified total strain energy model is proposed, and the precision of life prediction is higher than that of traditional fatigue model.