Simultaneous enhancement of mechanical properties and corrosion resistance of as-cast Mg-5Zn via microstructural modification by friction stir processing

Magnesium alloys are ideal lightweight materials ; however, their applications are extremely limited due to their low strength , poor ductility, and weak corrosion resistance . In the present study, a friction stir processing (FSP) treatment was employed to optimize the mechanical properties and corrosion resistance of an as-cast Mg-5Zn alloy. The average grain size of the Mg-5Zn alloy was refined from 133.8 µm to 1.3 µm as a result of FSP. Along different directions, FSP exhibited the enhancement effects on different mechanical properties. Furthermore, according to the potentiodynamic polarization results, the corrosion current density at the free-corrosion potential of the FSPed sample, was 4.1 × 10 −6 A/cm 2 in 3.5 wt.% NaCl aqueous solution, which was significantly lower than that of the as-cast sample. Electrochemical impedance spectroscopy revealed that the polarization impedance, R p , of the FSPed sample was 1534 Ω/cm 2 in 3.5 wt.% NaCl aqueous solution, which was 71.4% greater than that of the as-cast sample. The corrosion morphology of the FSPed sample in 3.5 wt.% NaCl aqueous solution exhibited largely uniform corrosion , rather than severe localized corrosion characteristics, which further reduced the corrosion depth on the basis of reducing the corrosion current density. The results presented herein indicate that FSP is a viable technique for simultaneously improving the mechanical properties and corrosion resistance of the as-cast Mg-5Zn alloy.