PNNL

Abstract

The increasing demand for high-strength, corrosion-resistant magnesium alloys in transportation has led to the development of new processing techniques. In this work, cast and extruded ZK60 magnesium alloys were processed using the innovative solid-phase process, Shear Assisted Processing and Extrusion (ShAPE). The microstructure was analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), showing a marked reduction in grain size, uniform solute distribution (Zn and Zr), and second phases after ShAPE processing. The corrosion resistance and electrochemical behavior were analyzed using potentiodynamic polarization, and atomic emission spectroelectrochemistry analysis (AESCE). Time evolution surface imaging and post-corrosion microstructures were also analyzed to support the understanding of underlying corrosion mechanisms. Corrosion initiation and propagation in ShAPE-processed samples followed grain boundary patterns, differing from cast and extruded ZK60 behaviors. Electrochemical measurements and in-situ time-dependent optical imaging demonstrated that ShAPE processing enhanced corrosion potential, reduced corrosion current, and increased cathodic activity. Additionally, ShAPE processing reduced the disparity in pitting potential between cast and extruded samples, resulting in intermediate pitting potentials. Higher Mg and lower Zn dissolution was observed in the lower anodic currents for ShAPE-processed samples. During aggravated anodic current cycles, Mg dissolution equalized, but the Zn/Mg dissolution ratio increased for ShAPE-processed extruded samples, suggesting less cathodic activation and better resistance to further pitting.