Study On Deposition Of PVD Coatings Onto Cast Aluminum Alloys And Their Corrosion Behavior

The use of wrought aluminum alloy in the 3C industry is very common, but the formation of wrought aluminum alloy needs complicated machining, and the cost is high. By die casting technology for preparing 3C appearance parts, costs will be substantially reduced, with the maturity of the die casting technology, market demand for die casting aluminum alloy is more and more urgent. ADC12 aluminum alloy studying in this thesis is the most used die cast aluminum alloy. Because of the poor wear resistance and poor corrosion resistance, it is usually necessary to surface treatment. However, the high silicon content in ADC12, the mass percentage of silicon content 9.6%~12%, limits the anodic oxidation process. Due to rich colors and excellent abrasion resistance, PVD process has a very broad market space for surface treatment of die casting aluminum alloy.Although the high silicon content of ADC12 die cast aluminum alloy can improve the casting property and mechanical properties, but it also caused the difficulty of cleaning process. Traditional cleaning solution contains nitric acid, hydrofluoric acid, in the production process nitric acid will produce toxic NO2 gas and volatile hydrofluoric acid also is harmful to human body. Therefore, cleaning solution with no nitric acid and hydrofluoric acid, which is environmentally friendly, is very necessary. Through testing a set of environmental cleaning solutions, we get an environmental cleaning process including three steps: alkali erosion, desumt, anti rust treatment.Because the aluminum alloy is soft, the Vickers microhardness of ADC12 used in this thesis is about 167 HV, direct PVD process cannot meet the demand of wear resistance and corrosion resistance of the production, therefore the surface hardening layer and PVD process are both used. During the test of surface hardened layer, three kinds of schemes are used, which are electroless plating, electroplating and thermal spraying, the morphology of the hardened layer, thermal stability, wear and corrosion resistance were tested. The final optimization is the electroless plating and PVD composite technology.The effect of electroless nickel plating with different thickness, microstructure on the subsequent PVD layer were systematically studied, PVD layer is Cr N film prepared by multi arc ion plating, by using Vickers hardness the hardness of the composite layer was tested, through a pin on disc friction and wear meter and scanning electron microscopy(SEM), the wear resistance of the composite layer were characterized, the corrosion resistance of composite layer was tested by electrochemical method, mainly to test the dynamic potential polarization curve and electrochemical impedance spectrum(EIS). It is found that the high temperature heat treatment of electroless nickel coating gets high final microhardness, but it is not beneficial to improve the adhesion and corrosion resistance of composite layer. The composite coating with high adhesion and corrosion resistance was obtained by electroless + PVD process. Compared with the reported results of PVD on the surface of Al alloy, in this topic the adhesion is more than 30 N.