Producing nano-grained and Al-enriched surface microstructure on AZ91 magnesium alloy by high current pulsed electron beam treatment

Abstract

Surface treatment of AZ91 magnesium alloy was carried out by high current pulsed electron beam (HCPEB) with accelerating voltage 27kV and energy density 3J/cm2. The surface microstructure and phase composition were characterized by using optical microscope (OM), X-ray diffraction (XRD), and scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). The surface microhardness and corrosion resistance were measured. Under HCPEB treatments, the preferential evaporation of Mg element occurred intensively on irradiated surface and the initial large Mg17Al12 phases were dissolved. The nano-grained and Al-enriched surface modified layer was ultimately formed of depth ∼8μm. According to the testing results, the surface microhardness increased from 63 to 141HK after 30 pulses of HCPEB treatment, while the best improvement of corrosion resistance was obtained by 15 pulses of HCPEB treatment with a cathodic current density decreased by two orders of magnitude as compared with the initial AZ91 sample.