Key Engineering Materials Vols. 373-374

Abstract: The titanium anodizations in 0.1 M sulfuric acid solution at different treated potentials and the effects of UV-irradiation on the anodized films were investigated by spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The results showed that the thickness of anodized films decreased in air within 280 min over 500 mV vs. Ag/AgCl. The features of parameters tanΨ and cosΔ in SE were in accord with the polarization curve and the thickness of anodized films, respectively. UV-irradiation could greatly decrease the thickness of the anodized films and provably assisted the reconstruction of anodized titanium films from an amorphous and porous structure to a compact structure. Regardless of UV-irradiation, the cosΔ and tanΨ were still in good agreements with the thickness of anodized films and the polarization curve, respectively. It was also found that UV-irradiation could decrease the surface roughness and make a wider atomically flat terrace on the anodized titanium surface.

Abstract: Electrodeposited Zn and Zn-Fe alloy have been applied widely to protect steel from corrosion, but the property of coating still needs to be improved. In this paper, Zn-Fe-SiO2 composite coatings are electrodeposited from Zn-Fe alloy electrolyte containing SiO2 particles. Zinc based coatings with Fe% >1%(mass) are deposited from sulfate bath, and coatings with Fe% <1%(mass) are deposited from chloride bath. Particle content in the composite coating generally increases with particle concentration under an adequate agitation and then tends to saturation. The optimum particle content in the composite coating is 0.5%(mass). Corrosion resistance, porosity, hydrogen embrittlement and surface morphology of Zn-Fe-SiO2 composite coatings have been tested and compared with electrodeposited Zn and Zn-Fe alloy. The data implies that Zn-Fe-SiO2 composite coating has the best corrosion resistance, lowest porosity, lowest hydrogen content and the finest crystal. All the results show that Zn-Fe-SiO2 composite coating is satisfactory to be used as anti-corrosion material for steel and has a great future in application.

Abstract: Electro-deposition Cu-In alloy can act as the precursor film to prepare CuInSe2 compound by selenating treatment. The effect of pH value on the electrodeposition potential of Cu-In alloy was investigated by electrochemical measurements in this paper. The relationship between the pH values and deposition potential was analyzed. Then uniform Cu-In alloy film was successfully prepared based on the special potential and pH.

Abstract: The properties of the conductive adhesive such as resistivity, shear strength and water -absorb ratio of the adhesive filled with the filler of Ag-coated graphite from electroless silver plating procedure were studied using the universal meter, the diagrams of scanning electron microscopy (SEM) and the shear strength testing. The results from the experiment showed that the resistivity of the Ag-coated flake graphite was relative lower when the addition was less than 50 % (wt) to that of the conductive adhesives filled with pure flake graphite. The shear strength of the conductivity adhesive filled with Ag-coated flake graphite was usually higher than that one filled with un-treated graphite and the peak values occurred when the filler addition was equal to 30%.

Abstract: In order to develop an environment-benignly chemical conversion process to substitute the toxic hexavalent chromium treatment on Al alloy surface, a new surface treatment technology based on rare-earth element, which is to form chemical conversion coating on 6063 Al alloy was presented. In this process, Ce(NO3)3 was adopted in the chrome-free preparing solution, and KMnO4 was used as oxidant to accelerate the coating formation on 6063 Al alloy. Furthermore, an L16(43) orthogonal experiment was carried out to examine the effect of Ce(NO3)3, KMnO4 and solution temperature on the coating growth on 6063 Al alloy. Accelerants of SrCl2 and NH4VO3 were added to the preparing solution to improve the coating performance. XRD, SEM and EDS were used to analyse the coating surface structure, morphology and composition. It was found that a good anti-corrosion coating which is mainly composed of the elements of Al, Ce, O, Mn, Mg could be formed in the optimal preparing solution of 5g/L Ce(NO3)3 , 4g/L KMnO4, 1.4g/L SrCl2 at the temperature of 20°C.

Abstract: In order to improve corrosion resistance of galvanized steel, a novel cerium-phytic acid passivation treatment was studied. The process of cerium-phytic acid passivation on galvanized steel was optimized. The corrosion resistance of cerium-phytic passivated samples was tested by dropping test and weight loss test. The electrochemical behaviors of cerium, phytic acid and cerium-phytic acid passivated samples in 0.5 mol/L NaCl solution were investigated by polarization curve and AC impendence spectroscopy, respectively. The corrosion equivalent circuit established according to impedance characteristics. The corrosion current density of the samples were treated by cerium and phytic acid was 8.52 × 10-5 A/cm2 and 9.39 × 10-5 A/cm2, respectively, However, the samples were passivated by cerium-phytic acid the corrosion current density decreased to 1.76 × 10-5 A/cm2, respectively. The test results showed that cerium-phytic acid passivated samples exhibited better corrosion resistance than that of cerium or phytic acid passivated sample under the same test conditions.

Abstract: NdFeB permanent magnets are highly susceptible to corrosion in various environments. A new composite coating electrodeposited on NdFeB magnets was investigated in this paper. The Ni matrix film was firstly electrodeposited on NdFeB surface from watts nickel electrolyte, and then Ni/Al2O3 composite coating was successively electrodeposited on the Ni film. The microstructures of electrodeposited Ni coating and Ni/Al2O3 composite coating were observed by scanning electron microscopy (SEM). The corrosion behavior of Ni coating and Ni/Al2O3 composite coating in 3.5wt% NaC1 solution was studied by polarization curves and electrochemical impedance spectroscopy (EIS). The results showed that the Ni coating and Ni/Al2O3 composite coating could both provide adequate protection to NdFeB substrate. But the free corrosion potential of Ni/Al2O3 composite coating was more positive and the passivation region was more obvious when compared with Ni coating. Meantime, the capacitance loop diameter of Ni/Al2O3 composite coating was significantly larger than that of Ni coating ,which suggested that the anticorrosion resistance of Ni/Al2O3 composite coating was better than electroplated Ni coating.

Abstract: The mainly process of electrochemical graining on 6063 aluminum alloy included graining at alternating current, anodizing and chemical coloring. The graining used NaBO2- H3BO3 system as film-forming solution, proper AC current density, treating time, temperature , adding agents and solution concentration were ascertained through operating orthogonal experiment, the grain of appropriate density and width could be obtained, the grained surface of aluminum alloy presented intergranular corrosion in the graining zone, the appearance was improved after anodizing, enough thick anodizing film could make intergranular corrosion eliminated. Cyclic voltammetry experiment was used to preliminarily explaine the grain process, the main cause of graining zone formation was hydrogen evolution.

Abstract: With suitable pretreatment, a compact and even nickel-phosphorus alloy coating was obtained on W-Cu alloy by electroless deposition from solutions containing nickel sulphate as a source of nickel and sodium hypophosphite as the reducing agent and a source of phosphorus. The Ni-P coating was normally prepared from acidic baths at high temperature of the order of 90oC with the pH of 4.8 and it was smooth and uniform and exhibited high crystal refinement and high microhardness and superior corrosion resistance. The microhardness, adhesion and corrosion resistance mechanism of Ni-P deposit were studied. The microhardness of the Ni-P alloy deposit increases greatly by tempering at various temperatures. The Ni-P deposit has a strong adhesive force with W-Cu alloy substrate checked by thermal shock test and scribe test. The anti-corrosion ability of Ni-P coating and its anti-corrosion mechanism were measured using immersion experiment and potentiodynamic polarization techniques. The results showed that the corrosion resistance of Ni-P coating was higher than that of W-Cu alloy substrate in the 10vol.% sulfuric acid, monitoring sweat solution and 3.5wt.% sodium chloride solution. The anti-corrosion mechanism of electroless Ni-P coating immersed in 3.5wt.% sodium chloride solution was studied using potentiodynamic polarization techniques. The surface micromorphological morphology and structure of the Ni-P coating were investigated using Scanning Electronic Microscope (SEM) and X-ray Diffraction (XRD). The results indicated that the Ni-P alloy coating consisted of microcrystals and it was amorphous in structure, and the electrochemical measurement showed passive film formed on Ni-P coating during immersion test in the 3.5wt.% sodium chloride solution.

Abstract: Nanostructured Ni-Al2O3 composite coatings incorporated with various contents of α-Al2O3 nano-particles were prepared on mild steel by using novel sediment co-deposition (SCD) technique. For the comparison reason, the pure Nickel coating and the Ni-Al2O3 composite coatings were fabricated by means of conventional electroplating (CEP) technique. The electroplating was carried out in Watt’s bath without any additives except for nano-α-Al2O3 suspension. The influence of the nano-particulates concentration, current density, and the mode of electroplating on the composite coatings were investigated. The results reveal that the weight percent of nano-Al2O3 increases with increasing nano-α-Al2O3 concentration in plating bath and some agglomeration occurs on the surface of composite coatings. The current density affects the alumina content in the composite coatings as well. The nano-α-Al2O3 incorporation by the SCD technique is higher than that of the CEP technique. The microhardness increases, while the wear rate decreases with increasing content of the nano-Al2O3 in the composite coatings. The incorporation of nano-α-Al2O3 particles changes the surface morphology of Ni matrix and modifies the texture of composite coating to exhibit a preferentially (111) growth orientation. Moreover, the co-deposited nano-sized α-Al2O3 particles are uniformly distributed in the Ni matrix and contributed to remarkably increase the microhardness, and tribological properties of the Ni base coating.