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Phosphating and Cathode Electrophoretic on the AZ61 Magnesium Alloy

Author: ZhouZuoZuo
Tutor: DuAiLing
School: Shandong University
Course: Chemical processes
Keywords: Magnesium alloy Phosphide Surface morphology Corrosion resistance Cathodic electrodeposition coating
CLC: TG174.4
Type: Master's thesis
Year: 2011
Downloads: 61
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Abstract


Magnesium alloy as a quality alloy structure material, widely used in the aerospace, automotive, electronic and medical equipment industries. But poor corrosion resistance of magnesium, which restricts the application of magnesium alloys. Magnesium alloy phosphate conversion coating has a porous structure, good adhesion, organic coating base. In this paper, the method of combining phosphating and cathodic electrodeposition coating to improve the surface properties of AZ61 magnesium alloy. Research methods, content and results of this study are described below. Select on the basis of domestic and foreign zinc phosphide research three different Phosphatizing system. By contrast, select suitable cathodic electrodeposition coating phosphating film of phosphate coatings obtained three phosphating system thickness, alkali resistance, surface morphology and elemental composition. Single factor test, respectively phosphating solution substances phosphide film-forming. The study shows that: Zn (H2PO4) 2 concentration of the thickness of the phosphate film have a greater impact, the greater the concentration, the larger the thickness; NaNO3 phosphating process having a role in promoting good; hydroxylamine sulfate is a good phosphating oxidation accelerator, and having the advantages of low dosage; NaF to promote phosphide, refinement layer. Favorable film-forming phosphide film of sodium metanitrobenzene and tartaric acid added, but the added concentration of film-forming conditions is less. Orthogonal design method design experiments, orthogonal table (L9 (34)), selected four concentrations greater impact on the substance NaF phosphating process, hydroxylamine sulfate, ZnH2PO4, NaNO3 four factors as orthogonal test The concentration of the substance to the level of each factor. The orthogonal optimization results: NaF concentration of 1.67 g · L-1, the hydroxylamine sulfate concentration of 1.5 g L-1, ZnH2PO4 the concentration of 23.1 g · L-NaNO3 concentration of 5 g L-1. AZ61 magnesium alloy surface formed in the the above optimization substance concentration phosphate coating thickness is moderate, Δw, good uniformity, low corrosion current density, and good corrosion resistance. Phosphating film on the basis of the above work, the above-described phosphating conditions for cathodic electrodeposition coating and the appearance (color, brightness, uniformity) preferably about 35μm in thickness and hardness of 2H-3H, and the substrate adhesion to 0, the composite electrophoretic coating with good corrosion resistance. Eddy current thickness gauge to measure the the phosphating film's thickness; using optical microscopy, scanning electron microscopy (SEM) observation phosphate coating surface morphology; chemical analysis method and EDS (EDS) analysis of phosphate coating composition ; by anodic polarization curve, electrochemical impedance spectroscopy (EIS), corrosion weight loss method to evaluate the corrosion resistance of the phosphate coating. The Electrophoresis part using eddy current thickness gauge measuring the thickness of the organic coating the EIS testing the corrosion resistance of the organic coating; national standards to measure the organic coating adhesion, hardness and solvent resistance.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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