Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/9865
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
以射頻磁控濺鍍純鋁及氧化鋁薄膜於鎂合金表面之抗腐蝕研究
作者: Lee, Ching Fei
李青霏
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
摘要: 
Abstract
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).

摘要
本研究以非平衡磁控濺鍍的方式,沉積純鋁及氧化鋁薄膜於AZ91D基材上,以熱處理的方式藉由鋁膜與基材間的固態擴散產生β(Mg17Al12)相的連續膜,改善其腐蝕性質;而氧化鋁膜則是以短時間沉積極薄的膜達到其保護效果,並進行表面結構觀察及腐蝕特性等分析。
由實驗結果可知試片在經前處理後其腐蝕電流有明顯下降,約略由300μA/cm2降至10μA/cm2。而經前處理後的試片鍍純鋁膜的腐蝕電流與前處理後的試片相近,並無明顯改善。將鍍純鋁膜後的試片做300℃熱處理;當試片以空冷的方式冷卻,膜與基材會有裂縫產生,且腐蝕性質變差;試片以爐冷的方式冷卻,膜與基材不會有裂縫產生。由低掠角X-ray的分析得知300℃持溫3小時其β相的相對強度最強。實驗發現熱處理後β相的連續和緻密與否,對其Ecorr及Icorr有其影響。本研究藉由改變試片熱處理升溫速率,得知當升溫速率快其β相較為連續且緻密;當升溫速率慢其β相較為不連續且較不緻密。
鍍30min氧化鋁膜由SEM觀察其膜厚約略是100nm,而經由腐蝕實驗得知其腐蝕電位(約-0.7V)及腐蝕電流(0.428μA/cm2)均有明顯改善。故其鍍純鋁膜後熱處理與鍍極薄的氧化鋁薄膜均可改善其抗蝕性。
URI: http://hdl.handle.net/11455/9865
Appears in Collections:材料科學與工程學系

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