Study On Technology Of Mechanical Plating

Sherardizing belongs to a thermal chemical process that is active zinc atoms into iron substrate. It’s a way of surface treatment that form Zn-Fe alloy sherardizing layer. Sherardizing have good uniformity layer, high corrosion resistance, and the advantages of the bonding strength is good. It application in track traffic, oil-gas transportation and marine industry. Traditional sherardizing because of the yield, low production efficiency of defects seriously restrict the development of its own.In this paper, based on the sherardizing after zinc plating. Through mechanical galvanized process, formation a layer of mechanical galvanizing layer at the substrate surface. Then, by means of thermal diffusion treatment to the sample, to form a layer of sherardizing layer on the substrate surface.The research content of this paper is as follows:(1) To determine the zinc diffusion coating process, and related process parameters, such as sealing medium, infiltration-aid, heating temperature and holding time. (2) Study about sherardizing, through optical microscope (OM), scanning electron microscope (SEM) to study the organizational structure of the coating permeability layer, through the EDS analysis of sherardizing layer of elements in the distribution of plating. Research the influence of such parameters on the sherardizing layer organization, and analyzes the formation process of sherardizing layer, by XRD analysis sherardizing layers of phase. (3) Study about bonding strength of the sherardizing layers by cross-cut test. Through immersion test, ac impedance test and polarization test study on the corrosion resistance of sherardizing layer.The results showed that:(1)At thermal diffusion process, use ground phosphate rock medium as sealing thermal is better, added 2Wt% boric acid in sealing medium could effectively inhibit oxidation. Thermal diffusion temperature in the range of 450℃ to 500℃, the heating temperature around 4h to obtain good thermal effect. (2) Sherardizing layer thickness distribution uniformity. Sherardizing layer structure, from outside to inside in the order is δk and δp, those two phase layer formed δ Phase Layer, and Γ phase layer is contains Γ1 and Γ2. The XRD analysis results of sherardizing layer organization show that coating on the surface is main FeZn6.67, FeZn8.87 and FeZn10.98, just like traditional thermal diffusion sherardizing. (3) The bonding strength of coating was good, but pure zinc layer on the surface of the bonding strength was poor. Polarization curve and impedance curve showed excellent corrosion resistance, just like traditional thermal diffusion sherardizing. Immersion test found, in 3.5Wt% NaCl solution, that sherardizing layer surface will produce a layer of corrosion product, can inhibit corrosion to continue.