Effect of Additives on Electrodeposited Aluminum Alloy Films By Using Dimethylsulfone As an Organic Solvent
Authors: Koiwa Ichiro , Matsubara Kyohei , Ito Yuya , Watanabe Nobuaki 
Published: February 2020

Aluminum alloy films have been electroplated by using Dimethylsulfone (DMSO2) as an organic solvent.　Several kinds of additives, Zinc (Zn), Iron (Fe), Nickel (Ni), Cobalt (Co), and Manganese (Mn), have been prepared. In this paper, the Aluminum-Zinc (Al-Zn) alloy films have been mainly focused. Aluminum Chloride, AlCl3, were used as aluminum source. Plating bath composition, mol ratio between DMSO2 to AlCl3 was 67:33. The alloy films were electroplated by using electrochemical measurement equipment, Hz-5000 made by Hokuto Denko Co. Ltd., and Al wire whose diameter was 1mm was used as a reference electrode. Aluminum plate (50mm x 10mm) was used as a counter electrode, both Cu (10mm x 5mm) and Ni (8mm x 6.2mm) substrates were used. Bath temperature was adjusted at 150oC by hot plated. Surface morphology was observed by scanning electron spectroscopy (SEM), VE-8800 made by KEYENCE Co. Ltd., film composition was determined by energy dispersive X-ray spectrometry, JCM-6000 made by JEOL Co. Ltd., and film structure was investigated by X-ray diffraction, RINNT2200 made by Rigaku Co. Ltd. Figure 1 showed effect of ZnCl2 concentration on Zn content of the Al-Zn films plated by three different current density, 3.0, 6.0 and 10.0 A/dm2. There were three regions, from 0 to 0.25 mol%, from 0.25 to 0.6 mol% and from 0.6 to 1.0 mol%. The zinc content gradually increased with increasing ZnCl2 concentration and reached at constant values less than 20 at% in the region from 0 to 0.25 mol% ZnCl2 concentration. On the other hand, the zinc content abruptly increased with increasing ZnCl2 concentration in the region from 0.25 to 0.6 mol% ZnCl2 concentration and the Zn content reached more than 90 at%. In the third region, the Zn content gradually increased with increasing ZnCl2 concentration in the region from 0.6 to 1.0 mol% ZnCl2 concentration and the Zn content reached almost 100 at%. The zinc content in the Al-Zn alloy films showed strong dependence on ZnCl2 concentration in the baths. However, the current density showed very little dependence on ZnCl2 concentration in the baths. There was one apparent result, Zn content in the Al-Zn alloy films plated by 6.0 A/dm2 current density showed higher values than those plated by 10.0 A/dm2 current density. The films plated by 3.0 A/dm2 current density showed maximum Zn content in the region less than 0.15 mol% ZnCl2 concentration and showed minimum Zn content in the region from 0.4 to 0.5 mol% ZnCl2 concentration. Therefore, zinc chloride concentration in the bath was more important factor than current density. Following results were obtained. The zinc-aluminum alloy films which were plated from the bath with low ZnCl2 concentration showed metallic luster, however, the alloy films which were plated at higher ZnCl2 concentration showed no metallic luster and showed gray. By scanning electron microscopy measurement, there were dendrite morphology for certain ZnCl2 concentration regions which were affected by current density. On the whole, the alloy films were composed with fine grains. By X-ray diffraction measurement, peak shifts, due to Al lattice, to lower angle side were observed. These results showed that the Zn atoms substituted Al atoms and formed a substitutional solid solution. There are three regions of the crystal structure change. First, degree of aluminum crystallization was deteriorated by codeposition of zinc. Second, alloy films which were plated at 3.0 and 10.0 A/dm2 current density showed alloy structure, however alloy films which were plated by 6.0 A/dm2 current density showed phase separation, Al and Zn. Third, zinc phase was matrix and Al grains were segregated in the Al matrix.

Figure 1