Corrosion behavior of an Al coating deposited on Mg alloy from AlCl3-EMIC ionic liquid

• Main Authors: Su-Yau Chen, 陳樹友
• Other Authors: Wen-Ta Tsai
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/94578204789265168181

碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 95 === 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.