Surface oxidation behavior of Mg-Y-Ce alloys at high temperature
- PDF / 162,911 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 6 Downloads / 246 Views
I. INTRODUCTION
MAGNESIUM alloys with low density have considerable potential as lightweight structural materials for the automobile and aircraft industry, but their extensive application has been limited due to their poor oxidation resistance. It is well known that magnesium oxide film may act as a protective layer preventing further oxidation at low temperature.[1,2] However, with the increase of oxidation temperature, the magnesium oxide film changes to porous structure and consequently loses its protective properties.[3–6] Commonly, the fluxes or protective gases (CO2, SO2, and SF6) are used to prevent magnesium alloys from burning during the melting process,[7–11] but the preceding methods have their disadvantages such as environment pollution, complication of casting equipment, cost inflation, etc. So, since the 1950s, much interest has been focused on the investigation of ignition-proof magnesium alloys. Beryllium and calcium were proved to be the effective elements to improve the oxidation resistance of magnesium alloys,[12–19] but ignition-proof magnesium alloys with enough beryllium and calcium additions have not been extensively applied in industry due to their poor mechanical properties and the smart toxicity of beryllium. Rare earths are often used as addition elements to improve alloys’ properties; especially, yttrium and cerium have been used in many alloys to improve oxidation resistance.[20–22] In the present research, the effect of yttrium and cerium additions on the oxidation behavior of magnesium alloys at high temperatures was studied so as to provide a new idea for the preparation of ignition-proof magnesium alloys. The microstructure of the oxide film on the alloys and its thermodynamic and kinetic mechanisms were investigated in detail. II. EXPERIMENT All alloys, i.e., Mg-Y, Mg-Ce, and Mg-Y-Ce, were prepared using commercial pure magnesium (99.9 wt pct), pure J.F. FAN, S.L. CHENG, H. XIE, W.X. HAO, and M. WANG, Graduate Students, and G.C. YANG and Y.H. ZHOU, Professors, are with the Northwestern Polytechnical University, Xi’an, Shaanxi 710072, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted March 15, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
yttrium (99.3 wt pct), and pure cerium (99.5 wt pct) elements. Magnesium alloys with different contents of yttrium ranging from 0 to 15 wt pct and cerium ranging from 0 to 15 wt pct were prepared in an electric resistance furnace under the protection of CO2-0.5 pct SF6 gas. The chemical compositions of alloys were analyzed by the inductively coupled plasma–atomic emission spectroscopy method. Samples with about 20 20 5 dimension were cut for ignition points testing directly after mechanical polishing and degreasing in acetone. Figure 1 shows the schematic diagram of the ignition point testing device, which was heated in air at the rate of 4 K/min in the present experiment. The crystallographic features were examined mainly by X-ray film diffraction with a Cu K source. The analyses of microstructura
Data Loading...
