Study On New Anodizing And Electrodepositing Technologies Of Titanium And Magnesium Alloy

Surface treatment technologies of titanium and magnesium were investigated in this paper. The anodization and electroplating of titanium alloys were researched (the second and the third chapters) and the anodization of magnesium alloys was studied (the fourth chapter).Titanium and its alloys as the most important engineering metal in 21 century are increasingly utilized in fields such as aviation, ship, automotive, medical treatment, chemical engineering on account of their excellent properties. However, poor wear resistance of titanium and easy contact corrosion with other metals restrict its engineering application. Enhancing the corrosion and wear resistance and decorative properties by appropriate surface treatment is significant. However, the conventional surface treatment technologies have some disadvantages, such as complex technique, high cost and toxic electrolyte. Two new processes of titanium surface treatment were studied in this paper and the main results obtained are presented as follows:1. A new pulse potentiostatic and arc-free anodizing process was developed. Smooth and compact anodic films with the thickness of about 2-10μm and the hardness of about 350-600HV on titanium alloys were prepared by this process. The effects of anodizing parameters such as electrolyte component and applied voltage on the process were researched. In addition, the morphologies of the films were investigated by scanning electron microscopy (SEM). The element distribution and phase composition of the films were also studied by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The results show that the film forming process and film properties were influenced by electrolyte component and applied voltage. Film analysis results show that the film was mainly composed of Ti and O, as well as Ni and P. The XRD picture had the diffractive peak of Ti and the crystal peak of TiO2. This indicates that the oxidation film was composed of crystal and non-crystal substances.2. A new process of direct electroplating on titanium alloy was developed. Nickel coating was electroplated by cathodic pulse current method on the surface of TC11 titanium alloy which was first activated through anodic pulse current in NiSO4 electrolyte containing metal complexing agent and anodic active additive. Influences of the components of the electrolyte and parameters of the technology on adhesion of coating to titanium alloy were investigated. The results indicate that TC11 titanium alloy would actively dissolve when 40g/L anodic active additive was added to NiSO4 electrolyte and 1.4A/dm2 anodic pulse current was used. A nickel coating with good adhesion to titanium alloy was obtained after switching anodic pulse current to cathodic pulse current. Influences of the average cathodic pulse current density, the average anodic pulse current density, frequency, concentration of the components of the electrolyte and other parameters on the quality of the nickel coating were studied in this paper. The process parameters were optimized as follows: nickel sulfate 80g/L, nickel chloride 40g/L, tri-natrium citric acid 15g/L, natrium dextrose acid 12g/L, boracic acid 35g/L, sodium chloride 20g/L, sodium fluoride 20g/L, temperature 60℃, pH 3.5, frequency 80Hz, ratio of Ton to T 20%, the average cathodic and anodic current density 1.4A/dm2. Magnesium and its alloys are increasingly utilized in fields such as aerospace, automotive, power tools and computer industries on account of their excellent properties including low density, high strength-to-weight ratio, excellent dimensional stability, high impact resistance and good thermal as well as electrical conductivity.Arc-free anodizing process was studied based on our previous research work. With the method of pulse potentiostatic and high current density, a layer of smooth, compact, high hardness and corrosion resistance anodized magnesium film was obtained. To the problems occurred in industrial production while using the new technology, such as copper ions resulted from the corrosion of copper rod that connected with cathode of stainless steel and local corrosion sites of the anodization films on magnesium alloys. Anti-interference of the anodization electrolyte to impurity ions and influences of the process parameters on the coating performances in the medium-size test were researched through lab experiment and in–site production.