Precipitation of Oxide Particles in Surface Mixed Layer of Al-Mg Alloys with a Trace of Ca During Oxidation

초록

Internal filling behavior of the mixed oxide layer of Al Mg alloys with a trace of Ca during oxidation by transmission electron microscope (TEM) was investigated. Containing a trace of Ca was done by Mg +Al2Ca master alloy as Mg alloying element. From the phase diagram of Al Mg Ca system plotted for oxygen partial pressure versus temperature, MgO would be the primary oxide the same as that of Ca-free alloy. A change by Ca containing is that CaMg2A116027 formation is involved in oxidation process of the alloy as the final product. After the oxidation at 515 C for 24 hrs under an air atmosphere, the oxidized surface of Al-7.5 mass% Mg-0.3 mass% Ca alloy was formed as the thickness with about 100 nm level and precipitated oxide particles with globular and rod-like shapes. From TEM-energy dispersive spectroscopy (EDS) results, it is considered that the oxide layer has the Ca-rich outmost area. From selected Area diffraction pattern (SADP) of oxide precipitation, an examined particle was identified as MgO2. Based on the phase diagram and results in this study, the oxide layer would be comprised of MgO, Al2O3, MgAl2O3-spinel and CaMg2Al16O27. Improvement of oxidation resistance by Ca addition may be attributed to interfiling effect among those oxides. As the oxidation proceeds, MgO2 precipitation could additionally occur by oxygen diffusion and contribute to maintenance of the oxide layer.

키워드