Effect of the high current pulsed electron beam treatment on the surface microstructure and corrosion resistance of a Mg-4Sm alloy

Highlights: • Surface modifications of a Mg-4Sm alloy by HCPEB were studied. • Mg₄₁Sm₅ nano precipitates formed in the HCPEB treated surface. • Corrosion resistance of 5 pulsed sample became worse due to the formation of defects and inhomogeneity on surface. • Corrosion resistance of 15 pulsed sample was improved due to the homogenized surface microstructure and composition. In the present work, the microstructure modifications and corrosion behaviors of a Mg-4Sm alloy treated by high current pulsed electron beam (HCPEB) with different number of pulses were investigated. The microstructure, composition and phase component in the treated surface layers were characterized by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). The results showed the dissolution of large Mg₄₁Sm₅ segregates, the formation of Mg₄₁Sm₅ nano-precipitates and twins in the surface layers after treatments. Electrical impedance spectroscopy (EIS) and polarization tests in the 3.5 wt% NaCl solution showed that the 15 pulses treated Mg-4Sm alloy sample exhibited the lowest corrosion current density, highest corrosion potential and polarization resistance among all samples. This is attributed to the homogeneous microstructure and composition with fewer defects in the surface layer after sufficient number of HCPEB pulses.