Study on the mechanism of melting oxidation of Zn-9Al-2.5Mg-Be alloy

Abstract

The oxidation resistance of Zn-9Al-2.5Mg-xBe (x=0,0.005,0.01,0.05,0.1) alloys was investigated in this study through isothermal oxidation experiments. The alloy microstructure, morphology, and composition of the oxide film were analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The oxidation kinetics and thermodynamics of Zn-9Al-2.5Mg were calculated, and the oxidation mechanism was discussed. The results show that the Zn-9Al-2.5Mg-0.05Be alloy exhibits a fine dendritic microstructure, with a large quantity of Zn-MgZn2 binary eutectic and Zn-Al-MgZn2/Mg2Zn11 ternary eutectic phases uniformly distributed. The Zn-9Al-2.5Mg-0.05Be alloy has the lowest oxidation rate among the tested alloys, with an oxide weight gain of 12 mg/m², which is only 0.67 times that of the Zn-9Al-2.5Mg alloy. The oxide film on the alloy surface is dense and retains the metallic appearance. The main constituents of the oxide film are Zn, Al, Mg17Al12, Mg2Zn11, and BeO, with no formation of Al2O3 or MgO. The oxidation mechanism of the Zn-9Al-2.5Mg-0.05Be alloy is attributed to the reaction of Be with oxygen, forming BeO, or the displacement reaction of Be with Al2O3 and MgO to form BeO, which inhibits the formation of Al2O3 and MgO.