Microstructure evolution and corrosion properties of ECAPed Mg–Pb-9.2Al-0.8B alloys

Abstract

Effect of grain refinement on corrosion behavior of Mg–Pb-9.2Al-0.8B alloy by equal-channel angular pressing (ECAP). By measuring open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS), the corrosion behavior of as-cast and ECAP samples in 3.5 wt % NaCl solution were compared and analyzed. The results showed that sample obtained fine crystal after ECAP, and grain refining reduced the corrosion resistance of the alloy. In the polarization test, the Icorr value was the largest, and the type changed from local corrosion to uniform corrosion. Two factors weaken the corrosion resistance: The first is that β-Mg17Al12 phase is homogenized by the tissue and disappears, thus losing the barrier of corrosion propagation, resulting in reduced corrosion resistance. The second is that Mg + Pb eutectic phase produced by thermal deformation is the first to be corroded. As a result, the corrosion resistance of the alloy decreases after ECAP.