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-MgZn _2 binary eutectic and Zn-Al-MgZn _2 /Mg _2 Zn _11 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 m ^−2 , which is only 0.67 times that of the Zn-9Al-2.5Mg alloy. The oxide film on the surface of the alloy is relatively dense and maintains the appearance of the metal. The main constituents of the oxide film are Zn, Al, Mg _17 Al _12 , Mg _2 Zn _11 , and BeO, with no formation of Al _2 O _3 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 Al _2 O _3 and MgO to form BeO, which inhibits the formation of Al _2 O _3 and MgO.

Keywords

• hot-dip alloy
• melt oxidation
• oxidation mechanism
• thermodynamic and kinetic oxidation
• characterization