Microstructure characteristics and corrosion behaviors of Mg-Gd-Ag-Y-Zn alloys with hybrid-deformation and aging treatment

Biodegradable Mg alloys (BMs) own remarkable clinical translations due to favorable bone remodeling capability and progressive degradability. However, there are still problems such as insufficient corrosion resistance, unclear formation mechanism of rare earth-containing film layers, and the need for further clarification of in-situ electrochemical corrosion response. Therefore, the correlations between microstructure characteristics and corrosion behaviors of different states Mg-Gd-Ag-Y-Zn alloys (as-cast, as-extruded, as-extruded-rolling and further aging treatment) were systematically elucidated by scanning electron microscopy (SEM), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), confocal laser scanning microscopy (CLSM), immersion and electrochemical evaluation. The aging-state magnesium alloys were processed by heat treatment at 200°C/8 h on the basis of hybrid-deformation Mg alloys to remove the internal residual stress. Results revealed that the rare-earth Mg alloy with extrusion-rolling hybrid-deformation exhibits a relatively homogeneous and fine-grained microstructure due to the intense dynamic recrystallization, compared to the as-cast and as-extruded deformation. The evaluation of static immersion and electrochemical corrosion both revealed that the samples with hybrid-deformation and further aging treatment exhibit the largest R ct (2178 Ω·cm -2 ) and the best corrosion resistance, with the corrosion rate of 0.796 and 3.74 mm·y -1 . The improvement in corrosion resistance is primarily driven by three sides. Firstly, the hybrid deformation promotes the formation of high boundary densities driven by recrystallization behaviors, and concurrently disrupts the large-scale rich-Gd/Y precipitates, thereby inhibiting the localized-corrosion reactions. Secondly, the hybrid-deformation coupled with aging treatment optimized the dispersive distribution of the precipitates, which further balanced the potential differences between α-Mg and the adjacent precipitates. Also, the products layer evolved from porous and loose to dense enrich-Gd 2 O 3 /Y 2 O 3 /Ca-P, thereby alleviating the adsorption and penetration channels for corrosive Cl - into the interior of Mg matrix.