Key Engineering Materials Vol. 751

Abstract: In this work, microstructure and corrosion properties of zinc electroplated steel before and after black chromating was investigated. The test samples were prepared by electrodeposition process, using a commercially-available alkaline electrolyte. Subsequently, the galvanized samples were applied with a black chromate-based passivation layer and a clear top-coat layer. Their microstructures were examined using X-ray diffractometry and scanning electron microscopy. The corrosion resistance of the samples was assessed with the salt spray test, following the ASTM B117, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization in 5 wt.% NaCl solutions. The study showed that zinc electroplated steels exhibit (110) crystallographic orientation. The passivation and top-coat layers did not affect the microstructure of the zinc layer, and covered uniformly on the zinc layer for all sets of samples. The corrosion resistant results obtained from salt spray testing and electrochemical testing revealed that the microstructure of zinc coatings prepared by using different applied current did not influence on their corrosion resistance markedly. While black passivation followed by top coating provided a significant improvement on corrosion resistance of the coatings.

Abstract: Electroless Ni-Zn-P coating with the optimal content of Ni and Zn in the alloy provides high corrosion resistance for steel. Ni-rich phase of this high hardness Ni-Zn-P alloy offers barrier protection property and sacrificial protection property is obtained from the alloy with proper content of Zn. In this work, the Ni-Zn-P coatings were prepared on steel substrates by using alkaline electroless deposition. The parameters of deposition process including complexing agent concentration, bath pH, zinc ion and nickel ion concentration were systematically studied. The microstructural morphology and elemental composition of the coatings were characterized by scanning electron microscopy. It was found that complexing agent, zinc ion and nickel ion concentrations play important role on Zn content of Ni-Zn-P alloy whereas alkalinity of the solution bath directly affects the deposition rate. The results of corrosion resistance investigated by linear polarization illustrate that the corrosion potential (E_corr) of Ni-Zn-P coatings is negatively shifted by an increase of Zn content in the alloys. From this work, E_corr of 83%Ni-11%Zn-6%P coating prepared in this system is slightly lower than steel. To achieve a higher effect of sacrificial protection for corrosion protection of steel, Ni-Zn-P with higher content of Zn should be further studied.

Abstract: Brake pad is the combination of lining and metallic components, e.g. steel backing plate (disc brake) and aluminum brake shoe (drum brake). Shear bond strength plays a major role to provide the safety and/or drive performances. This work aimed to study the processing factors affected the bonding strength. The molding temperature couple with post-curing temperature was simultaneously analyzed in order to optimize the processing temperature. The shear bond strengths of metallic plates were continually investigated with regard to the effect of different surface treatments. The obtained results indicated that the mechanical strength was increased as the molding temperature raised in ranges of 160°C to 180°C. Conversely, the deterioration of adhesive strength was progressively presented with rising post curing temperature. In comparing different backing plate, aluminum showed the higher shear bond strength than that of steel plate. In fact, the weakened property of aluminum in nature would be easily destroyed by mechanical treatments. From the shear tested results, an increase of surface roughness was inversely changed the shear bond strength. On the other hand, the contact angle of water droplet affected directly to adhesive strength. It was suggested that an adding surface roughness, commonly used in automotive industry, was inappropriate criteria, whist geometrical surface should be taken into account for improving the shear bond strength. Moreover, the contact angle and mechanical interlocking were recommended to use as a criteria of brake pad shear strength.

Abstract: TiO₂ thin films coated on glass substrates for self-cleaning applications were prepared by sol-gel dip-coating technique. The influence of annealing temperature and air exposure time on wettability was investigated by a water contact-angle measurement. Thermal annealing at temperatures of 100, 200 and 300 °C in air were conducted to the films. Surface morphology of the films was observed by FE-SEM. Elemental distribution and optical properties were examined by EDX mapping and UV-Vis transmission spectroscopy, respectively. Atomic bonding was confirmed by FTIR. The contact angle reached a maximum when the films were annealed at 200 °C. The contact angles of the as-synthesized films were 61.4±2.7°. During storage in air for 20 days, the contact angles increased to 143.1±2.1°. The films were further reannealed with 100 °C for 20 min, the contact angles were enhanced to 153.1±1.3°. The association of contact angle among the surface morphology, elemental distribution and atomic bonding of the films will be discussed.

Abstract: This paper presents the use of meta-heuristics one of the most popular types of optimisation methods for solving real engineering applications. The general procedure of meta-heuristics is detailed. The applications are related to metal forming processes. Two design examples, optimisation of a strip coiling process and the non-circular wire drawing process, are demonstrated. The results obtained are compared while advantages and disadvantages of using the optimisers are discussed.

Abstract: A hydrocyclone is a device used widely in various industries, especially for separation of solids from liquids. Many factors affect the separation efficiency of a hydrocyclone. In this research, the main objectives were a study of the conical length that affected the separation efficiency and proposal of a regression model of Stk₅₀Eu for a hydrocyclone. First, research was performed on the separation efficiency using a 40-mm hydrocyclone. The effects of conical lengths of 200, 240 and 280 mm were investigated. The tested suspension was a mixture of silica and water. The silica particles have an average size of 9–10 μm at a solid concentration of 0.5% w/v. The feed-flow rate of 1 m³/hr was operated with the constant flow ratio of 0.1. From the experimental result, it was found that the shorter conical length obtained the higher separation efficiency. For a conical length of 200 mm, the cylindrical length of 60 mm and the vortex finder length of 40 mm showed the best separation efficiency, up to 84.06%. Second, a regression model of Stk₅₀Eu of the hydrocyclone was established. In this work, data obtained from a total of 75 experiments in the first part and from earlier research were used to form the relationship between the dimensions of the hydrocyclone and Stk₅₀Eu. The calculated Stk₅₀Eu can successfully be used to predict experimental Stk₅₀Eu.

Abstract: Stereolithography is a manufacturing process capable of building a truly high resolution 3D structure by solidifying the liquid monomer in a layer by layer fashion. Currently, there are many developments toward new 3D printing techniques leading to needs for methods of characterization to improve printing process for higher performance. In this study, we propose to create a bottom-up projection stereolithography to accommodate a 3D printing technique. Our system was designed for combining with a regular fused deposition modeling (FDM) process for multi-material application. In addition, we developed a method for characterizations different specifications of a custom-made projection stereolithography. Our 3D printer can create an object up to 25 mm x 25 mm x 15 mm of length, width and height, respectively. We minimized the layer thickness error by modifying a screw and spring components in order to precisely control the movement of the vertical stepping. The light source distance and the calibration factor were also importance factors to obtain the better precision of finished parts. Based on the proposed characterization method, the 3D printer was able to achieve the lateral resolution of 0.05 mm and a vertical step resolution of 0.01 mm. The average percentage error of built part were 0.32 % on X-axis and 0.25 % on Y-axis laterally and 0.60 % error on the layer thickness.

Abstract: In this work, the experimental and numerical analyses of Forming Limit Curve (FLC) and Forming Limit Stress Curve (FLSC) for Advanced High Strength Steel (AHSS) sheet, grade JAC780Y, are performed. Initially, the FLC is experimentally determined by means of the Nakazima Stretch forming test. Subsequently, the FLSC of investigated steel was plastically calculated using the experimental FLC data. Different yield criteria including Hill48, and Yld89, are applied to describe plastic flow behavior of the AHS steel and Swift hardening law is taken into account. Hereby, influences of the constitutive yield models on the numerically determined FLSCs are evaluated regarding to those results from the experimental data. The obtained stress based forming limits are affected significantly by the yield criteria. Finally, the experimental and numerical formability analyses of Fukui stretch-drawing and square cup drawing tests are studied through FLC and FLSCs. It is observed that all stress based curves can be used very well to describe material formability of the examined steel compared to the strain based FLC. The strain based FLC depend on forming history and strain paths change. In the other hand, the stress based FLC do not depend on these issue. In this study, it can be concluded that the FLSCs could predict failure more realistically and better than the strain based FLC.

Abstract: Many studies of hydrocyclones have confirmed that increasing the feed-flow rate results in a higher separation efficiency. The purpose of this study was to investigate the separation efficiency for a 100 mm solid–liquid hydrocyclone with 1 and 2 wt% solid concentrations at feed-flow rates of 2, 3, 4, 5 and 6 m³/hr. The solid concentration and particle size distribution were analysed using drying–weighing and a particle-size analyser (Mastersizer 2000), respectively. The experimental results indicated that an increase in feed-flow rate from 2 to 4 m³/hr produced decreased separation efficiency. However, when the feed-flow rates increased from 4 to 6 m³/hr, the separation efficiency increased. Furthermore, the higher the feed-flow rate, the smaller the cut size. A novel separation efficiency equation in terms of the concentration ratio and flow ratio is also proposed.

Abstract: Bending and hemming process are used in automotive industries for assembling the car body panel.The main failure mechanism under bending loads is the intercrystalline fracture. This is due to the fact that the Forming Limit Curve (FLC) describes first occurrence of membrane instability and no material failure in consequence of an intercrystalline fracture at bending.The FLC fails to predict the formability in hemming processes since difference in failure mechanism. A new failure criterion, the so-called Bending Limit Curve (BLC) has been developed. In this work, the left hand side BLCs are experimentally determined for Advanced High Strength Steel grade DP1000, Stainless Steel grade SUS430 and Deep Drawing Steel grade SPCC having a thickness of 1.0 mm. The influence of various bending radii and level of pre-strain on the bending strains are investigated and discussed by using the Three Point Bending Test. Bendability of investigated materials are evaluated by using optical strain measurement system GOM-Aramis to determine maximal achievable bending strain on the specimens. The developed left hand side BLCs were found to be higher level than conventional FLCs. The bigger bending radius established lower bending limit strain. The higher bending strain was obtained from the higher pre strain level.