Effect of temperature on microstructures and properties of aluminized coating on pure magnesium

Surface aluminizing on pure magnesium was conducted by diffusion aluminizing treatment in vacuum at 673 K, 693 K and 718 K. The microstructures and phase constituents of the aluminized coating were investigated using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy disperse spectrometry (EDS). The results revealed that an Al-rich coating had been formed on the surface of magnesium specimens by the solidification of the liquid layer formed between the magnesium substrate and the aluminum particles. The microstructure of the aluminized coating was typical hypoeutectic structure, which contained a large amount of intermetallic compound, such as beta-Mg17Al12. The composition profiles and microstructures of the aluminized coating were depended on the heating temperature. The results of micro-hardness tests indicated that the micro-hardness value of the specimen's surface increased due to the formation of the intermetallic compound. The results of immersion corrosion tests and electrochemical corrosion tests in 5 wt.% NaCl solution showed that the corrosion resistance of the coated specimens had been increased significantly, for example, the open circuit potential changed from -1.250V (vs. SCE) to -0.866V (vs. SCE) and the corrosion current density decreased from 1.3 x 10(-3) mA/cm(2) to 1.0 x 10(-4) mA/cm(2). Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.