In-situ preparation of (Ti,Al) codoped blue PEO ceramic coating on magnesium alloy and chromogenic mechanism

Abstract

In this paper, the blue ceramic coating was prepared in situ on the surface of AZ31 magnesium alloy using Ti and Al composite salt as electrolyte by PEO technology. The results show that the light wave response range of the prepared ceramic coating is all in 430–470 nm with different n(Ti)/n(Al) atomic percentage in the electrolyte, but the blue color saturation of the ceramic coating increases with the increase of n(Ti)/n(Al) ratio. XRD and XPS analysis show that Ti exists in the form of Ti4+ and Ti3+, Al exists in the form of Al2O3, and a small amount of Ti3+ ions occupy the Al3+ lattice in the form of replacement solution, forming (Al2-xTix)O3 solid solution. This is the chromogenic mechanism of PEO-MgO ceramic coating changing from off-white to blue. Finally, due to the PEO plasma discharge generated on the surface of magnesium matrix in the micron level spot melting pool, the formation of the blue material of Al2O3 doped with Ti and the oxidation and sintering of magnesium matrix at high temperature synchronously, thus achieving in situ color ceramic treatment on the surface of magnesium alloy with low melting point.