Studies On Aluminium Alloy Surface Pretreatment Technologies Of Zinc-dipping And Galvanizing Zinc

As one of the important surface treatment technologies, electroplating is an electrochemical method, which can modify the surface characteristics. Electroplating aims at changing surface properties or size of the substrates by plating metal coats on them, such as increasing anti-corrosion, micro-hardness, anti-abrasion, electrical conductivity, lubricity, heat resistance and decorative property etc.At present, the electroplating technology on aluminium and its alloys is applied widely as one of the important surface treatment methods of aluminium. Aluminium is a metal which is difficult for plating, oxide film can easily form on its surface, which is a bad factor for electroplating, so pretreatment is very important for aluminium. But the conventional method has many disadvantages such as complex operating process, bad activation for aluminium surface, expensive cost, environment pollution etc. In this paper, regarding to the above problems, new pretreatment methods for aluminium alloy 3005 have been studied to develop new aluminium electroplating technologies. The main results obtained are presented as follows:1. Aim at the defects of the twi-Zn immersion technology such as complex process, immersion plating quality control problem, low rate of finished product, and too thick zinc dipping film, a one-step zinc dipping process was developed to improve the zinc dipping coat quality by adding an effective anodic additive to eliminate the oxidation film and using an electrochemistry method of anodic assistance, This process can obtain a flat of zinc which is thin and uniform. Then, the excellent continuative coat would be obtained by electroplating on the bottom zinc layer. Effects of the one-step zinc dipping solution components, operating conditions and process parameters on the coat performances were detailedly discussed in this paper, and the surface morphologies were analyzed by scanning electron microscope (SEM). This process not only gets rid of some defects of the conventional zinc dipping process, but also has many advantages, for example, simple operation, simple composition, easily controlled etc.2. A process of electrodepositing zinc mesosphere on aluminium in subacidity solution was studied in this paper. In this process surface activity of aluminium was improved by anodic polarization process and electordeposition was carried out in the same bath. The zinc film after acid etching also can be used as pre-coating film of aluminium. Compared with twi-Zn immersion method, the operation of this process is more simple, and bath control is easier, equipment corrosion is less what is more important is that this process can be operated at ambient temperature. The influences of the bath components and process parameters on pretreatment process were discussed in this paper.3. Electrochemistry assistance has been used in alkaline zinc plating process, anodic activation used to assist dissolution of aluminium oxide film in alkaline solution. Through improving the anodic activation effect and extending the anodic activation current density, this method was used to pretreat complex workpieces. Influences of solution components, process parameters and operate conditions on the pretreatment effect were studied. This technology has many advantages such as simple process, simple bath component, wide applicability and ambient temperature operation.