Improvement of corrosion resistance of magnesium alloy by high-temperature high-pressure cavitation treatment

In this study, basic research on the formation of a film for improving the corrosion resistance of a Mg alloy (AZ31) surface was carried out by the addition of dilute phosphoric acid during water jet peening (WJP) and multifunction cavitation (MFC). These mechanochemical (MC) processes are referred to as MC-WJP and MC-MFC, respectively. MC-WJP and MC-MFC processing formed a film on the AZ31 alloy surface that contained phosphate compounds, including oxides, hydroxides, and carbides. Because MFC or WJP processing forms fine cracks on the alloy surface, we concluded that a thick film was formed on the “MC” surfaces because phosphoric acid adhered to these cracks. The film formed on the surface processed by MC-MFC was thicker than that formed on the MC-WJP processed surface because the former process produces higher-temperature cavitation bubbles. Keywords: Multifunction cavitation, Water jet peening, Mg alloy, Corrosion resistance, Phosphate film, GD-OES