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標題: A Study on the Corrosion Properties of AZ91D Mg-Al-Zn alloy deposited Al and Al2O3 Films by Radio Frequency Unbalance Magnetron Sputtering Technique
作者: Lee, Ching Fei
關鍵字: RF unbalance magnetron sputtering;非平衡磁控濺鍍;corrosion property;solid diffusion;corrosion current;pre-treatment;腐蝕性質;固態擴散;腐蝕電流;前處理
出版社: 材料工程學研究所
Magnesium alloy has not been used as widely as aluminum, partly because of its poor corrosion resistance. In this study, aluminum and alumina thin film were deposited on the AZ91D substrate by radio frequency unbalance magnetron sputtering technique. The Mg17Al12 β film was formed due to solid diffusion between aluminum film and substrate after heat treatment. The alumina thin film was deposited on AZ91D substrate, and the alloy's corrosion performance was substantially improved. HF/H2SO4 pre-treatment is effective for reducing the Icorr value of die-cast AZ91D. Experimental results showed that Icorr decreases from 300μA/cm2 to 10μA/cm2 after pre-treatment. Aluminum film deposited on the pre-treated sample can not further decrease the Icorr value. Heat treatment for the Al film/pre-treated AZ91D sample was performed to obtain a Mg17Al12  phase right beneath the aluminum film. It was found that heating at 300℃ for 3hr will result in the formation of Mg17Al12 β phase. However, small cracks occurs while the sample cooling in air after heat treatment, leading to inferior corrosion performance. The sample will not have cracks while furnace cooling is carried out after heat treatment. The study found that a continuous β film covering the substrate will improve corrosion performance. Heating rate is an important factor to control the morphology of the β phase. When low heating rate was applied, β phase in irregular shape will form beneath the aluminum film, leading to severe corrosion. Alumina film with 100 nm in thickness, which can effectively protect the AZ91D alloy, resulting in high Ecorr (-0.7V) and low Icorr (0.428μA/cm2).

Appears in Collections:材料科學與工程學系

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