Al-Zn Alloy Formation from Non-Aqueous Solution By Electrochemical Technique

Introduction

 At present, the hot dipping of Zn-Al, uses to suppress the corrosion of the steel. In addition, Al-Zn alloy become a high strength material such as duralumin by making the alloying with Mg and Cu.

 An aluminum, that is less noble than hydrogen is, not able to be electrodeposited from aqueous solution.¹⁾Therefore, the electrodepositions using ionic liquids or non-aqueous have been studied. However solution such as toluene, which has a risk of causing a spontaneous combustion because of it’s high flammable. An ionic liquids are salts whose melting point less than 100 ℃. Since the solution has very high electrical conductivity, high stability and, low volatility, it is suitable for plating solvent.

 In this study, we report on the results of the plating of the Al-Zn alloy films from the plating bath with AlCl₃, ZnCl₂ and dimethyl sulfone (DMSO₂).

Experiment

 The plating solution was composed of AlCl₃, ZnCl₂ and DMSO₂. The total metal chloride ratio, (AlCl₃ + ZnCl₂) / (DMSO₂ + AlCl₃ + ZnCl₂), is constant at 33.3 mol%. The ratio of ZnCl₂ to AlCl₃ is controlled from 0.005 to 1.0 mol%. A current density is 600A/m². The acid activating (RT, 1min) after alkaline degreasing (60 ℃, 5min) is performed as pretreatment process. The plating was performed at 150 ℃ for 30 minutes. As analysis method of sample, we used X-ray diffraction (XRD), energy dispersive x-ray spectrometry (EDS), X-ray photoelectron spectroscopy (XPS).

Results and Discussion

Effect of bath composition

 As a result of changing the bath composition, metallic gloss plating film was deposited up to 0.05 molar percent metal salt concentration of Zn. The gray film was obtained in 1.0 molar percent.

Results of by EDS

 The composition of the deposited Al-Zn alloy plating films was estimated by using EDS. The content of Zn is increased with increasing the concentration of the metal salt Zn. 

Result by X-ray diffraction (XRD)

 Figure 1 shows an XRD pattern of the sample. The peak of the Al can observed without the sample of 0.1 molar percent of Zn salt.

 Figure 2 shows an enlarged view of Al (200) peak area. With increasing of the Zn metal salt concentration, the diffraction peak is shifted to a lower angle side, and the half width is increased. An atomic radius of Zn and Al are 125 and 135 pm, respectively. The diffraction peak will be shifted to high angle in accordance with Vegard’s low, when Zn is replaced by Al site. The increase of half width shows deterioration of crystallinity.

Acknowledgements

 This work was partially aided by MEXT-supported Program for the Strategic Research Foundation at Private Universities.

References

1. T. Hirato, J. Fransaer, and J. P. Celis,

          J. Electrochem.Soc., 148, C280 (2001).