Microstructure and corrosion resistance of AZ91D magnesium alloy treated by hybrid ion implantation and heat treatment

In order to improve the corrosion resistance of magnesium alloy, solid solution-aging treatment and then nitrogen and aluminum (N/Al) duplex ion implantation was conducted on AZ91D magnesium alloy surface. X-ray diffraction (XRD), scanning electronic microscope (SEM) with energy dispersive X-ray spectrometer (EDX or EDS) analysis, Auger electron spectroscopy (AES), electrochemical workstation and microhardness tester are used to characterize the surface microstructure, phase composition, atomic concentration-depth distribution, corrosion resistance and microhardness, respectively. XRD results show that the surface modified layer includes Mg, Mg17Al12, MgAl2O4 and AlN phase, the diffraction peak position and intensity of Mg and Mg17Al12 shift obviously. AES analysis indicates that 280 nm modified layer exists in the surface and near surface. Compared with the substrate, the microhardness of solid solution-aging sample and solid solution-aging combined with duplex ion implantation sample increases by 16.7% and 36.6%, the polarization resistance Rp increases by 20.6 and 107.3 times, respectively. The corrosion current intensity (icorr) decreases by two orders of magnitude in 0.56 M NaCl solution. SEM observation exhibits that duplex ion implantation sample shows less corrosion pit, but untreated and solution-aging coupons have a large amount of corrosion pit under the same corrosion conditions.