本研究主要探討利用AlCl3-EMIC離子液體(ionic liquid)，在室溫下之鈍態環境(glove box)中，分別以定電位與定電流方式於壓鑄AZ91D鎂合金表面電鍍一鋁鍍層，並探討施加不同之電位與電流值對鋁鍍層表面形貌、厚度、化學成分及結晶結構之影響。最後，以電化學試驗，分析不同條件下備製之鋁鍍層電化學性質及其抗蝕能力差異。

本研究中以掃描式電子顯微鏡(Scanning electron microscopy, SEM)對鎂合金原材與鋁鍍層顯微結構進行觀察，並輔以能量散射光譜(Energy dispersive spectroscopy, EDS)鑑定鍍層之化學組成。鍍層之結晶結構則利用X光繞射分析儀(X-ray diffraction, XRD)。針對鍍層電化學性質，則將試片於室溫中浸置於3.5 wt%氯化鈉水溶液中，利用恆電位儀(Potentiostat 263)進行開路電位測試(Open circuit potential, OCP)及動電位極化測試(Potentiodynamic polarization)；另一方面，於相同測試環境中，利用頻率分析儀(Frequency Response Analysis 1255, FRA 1255)進行電化學交流阻抗頻譜測試(Electrochemical impedance spectroscopy, EIS)，藉以了解鍍層之耐蝕能力。

實驗結果顯示，未經過處理之鎂合金原材由鎂固溶相(Mg solid solution, α)與介金屬化合物(Intermetallic compound, Mg17Al12)所組成，分別經恆電位與恆電流方式電鍍之後，鎂合金表面均生成一鋁鍍層。然而，於電鍍過程中，施加較低之電位(-200 mV)或電流值(-15,-20 mA/cm2)，從表面形貌觀察均可獲得一連續、緻密且具結晶性的鋁鍍層，從橫截面觀察發現鋁鍍層與鎂合金原材間具良好的附著性；另外，上述鋁鍍層經過XRD分析顯示，於此條件下，鋁鍍層主要以(111)進行生長。相反的，當施加較高之電位(-400 mV)或電流值(-40 mA/cm2)時，其鋁鍍層形貌類似瘤狀物，橫截面顯示鍍層比較不平整且與基材間之附著性不佳，其XRD結果顯示其生長方式較以(200)為主，顯示鋁離子之沉積速率對鍍層表面形貌及其結晶結構具關鍵性的影響。

電化學分析結果顯示，鎂合金原材之抗蝕性不佳。然而，於鎂合金表面電鍍一鋁鍍層後，鋁鍍層之開路電位較鎂合金原材有明顯提升，且經動電位測試後，有鈍態區域(Passive region)的生成，且經電化學交流阻抗測試後顯示，鋁鍍層之阻抗值明顯地較鎂合金原材高，顯示鋁鍍層能有效阻絕環境對鎂合金之腐蝕。

Electrodeposition of an aluminum coating on the die-casting magnesium alloy (AZ91D) in AlCl3-EMIC at 25 ℃ has been investigated in this study. Parameters of several current densities/potentials applied to the effect composition, structure and corrosion behavior of aluminum coating was analyzed.

Morphologies and chemical compositions of a bare Mg alloy and Al-coated specimens were examined in a Philip XL-40FEG SEM and its auxiliary energy dispersive spectroscope (EDS). X-ray diffraction (XRD) analysis was also performed with a Rigaku diffractometer to explore the crystal structure. Besides, the corrosion behavior including of open circuit potential (OCP), electrochemical impedance spectra (EIS), and polarization curves of the specimens were measured in 3.5 wt.% NaCl solution using a Solatron 1255 + 263 Potentiostat electrochemical measurement system.

The results showed that a bare Mg alloy was dual-phase structure,consisting of α-Mg and Mg17Al12. After electrodeposition by applied a series of potentials and current densities. An Al-coating layer was deposited on the AZ91D substrate. In the case of applied low potential/current density(-200 mV and -15, -20 mA/cm2) in the electrodeposition, a quite dense and well adhesive Al layer was obtained. XRD showed the preferriental grown on the (111) surface. However, the nodular Al layer grown with relatively poor adhesive was obtained on the (200) by using higher potential/current density(-400 mV and -40 mA/cm2) in the electrodeposition. Consequently, the beneficial effect of the Al-coating varies with the film structure which greatly depends on the electrodeposition condition.

The corrosion resistance of the Mg alloy with and without Al-deposition was also evaluated in 3.5 wt% NaCl solution. The results showed that the corrosion resistance of the Mg-alloy substrate is very poor, but it can be improved after Al-coating deposited on the alloy, having an increase of OCP and polarization resistance. A passive film was abserved in the Al-coating alloy in the potentiodynamic polarization test.

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