JOURNAL OF NEW MATERIALS
Year:2012 | Volume:2 | Issue:4 (8)|Papers Count:8

Low temperature phosphating is a very slow process and needs to be accelerated by some means. Acceleration of the phosphating process could be achieved by chemical. mechanical and electrochemical methods. In this paper, the effect of mechanical surface preparation such as surface grinding by 180 grade emery paper. sand blasting and shot blasting on the quality of zinc phosphate coating was investigated. Scanning Electron Microscopy (SEM) investigations showed that the very rough shot blasted surface is not suitable for getting a compact and fine-grained coating. In contrast, surface preparation by sand blasting produces a great number of active sites on the substrate which resulted in a higher rate nucleation, and thus reduction of final sizes of phosphate crystallites in comparison with what obtained by grinding operation. Also, measuring thickness, weight and density of applied Phosphate coatings, revealed that the surface activation by sand blasting, leads to formation of dense and light weight coatings at shorter time of phosphating.

The work here investigates the correlation between microstructural features and mechanical properties of similar and dissimilar resistance spot welds of low carbon steel (LCS) and dual phase steel (DP600) in the tensile-shear test. Correlations between the critical fusion zone size required to ensure pullout failure mode, the weld microstructure and the weld hardness characteristics were developed. Results showed that the critical fusion zone size is a function of hardness profile characteristics (ratio of fusion zone hardness to average hardness of the base metal). Expriments showed that similar DP600/DP600 and dissimilar DP600/LCS welds exhibit the highest and the lowest tendency to fail in interfacial failure mode, respectively. Finally, peak load and energy absorption of similar and dissimilar resistance spot welds are compared.

In order to improve corrosion resistance of 2024- T3 aluminum alloy, anodizing process was performed in different concentrations of mixed-electrolyte of sulfuric, boric and phosphoric acids for 10 and 20 minutes under the current density of I and 2 mA/cm2 at room temperature. Corrosion behavior of the anodized alloy in aqueous media containing 3.5 wt% of NaCI was studied by using electrochemical impedance spectroscopy technique and the corrosion parameters were determined by using of an appropriate equivalent circuit. Thickness of the oxide layer was determined by a simple method using electrochemical impedance spectroscopy technique. Finally, in order to compare the corrosion rates of the anodized samples, Tafel extrapolation technique was used. The results revealed good corrosion resistance of the alloy which was anodized in mixed-electrolyte. This electrolyte is a suitable replacement for chromate baths which are generally used in anodizing of 2024- T3 aluminum alloy.

Metal cutting can be associated with high heat generation in the tool-chip interface zone and hence, the thermal aspects of the cutting process strongly affect the accuracy of the ultra precision machining. This study presents the effect of tool edge radius and cutting speed on heat generation and balance of energy in nanomachining process using three dimensional molecular dynamics simulation with Embedded Atom Method (EAM) metal potential energy. Results show whenever tool scratches the work material, atoms velocity of surface layers is increased dramatically, which influence kinetic energy and workpiece temperature. By increasing cutting speed to 400%, cutting forces are increased between 21-27%. Although tool forces is not increased considerably by cutting speed, a big fraction of potential energy, kinetic energy and heat transfer are remained in workpiece. So, workpiece temperature and temperature gradient is increased dramatically. Increasing cutting speed form 50 m/s to 200 m/s affect on temperature increment near machined surface from 300oC to 700oC which can affect the surface roughness. In addition, tool edge radius increases in contact area between tool and workpiece when tool fore is increased especially in trust direction. Consequently, temperature gradient is raised locally in chip formation area by tool edge radius.

Thin film of ZnO was synthesized on a glass substrate via sol-gel method. The crystal structure and surface morphology was studied, using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The size of crystalline particles formed on the surface were calculated using Scherrer's equation and the X'pert High score software, and was estimated around 30 nm. Using synthetic coating, metal oxide gas sensors were fabricated and the sensitivity of the sensor to the two common gases of O2 and CO2 were analyzed. The results showed that the porous coating of zinc oxide is very sensitive to the gases. Also, the response time for the two gases, were calculated. Response time for CO2 was twice of the O2, and about 12 seconds.

Composite CNG tanks have a number of advantages such as high gas pressure, safer failure modes, higher mechanical properties, higher corrosion resistance, as well as being 2 to 4 times lighter than steel tanks. The main aim of this work is the thermo-mechanical analysis and evaluation of Type Ill composite CNG tanks. A high-performance hot-cure Araldite epoxy resin system was selected and modified as the matrix. The T-700S high-strength carbon fiber was also selected as the reinforcement. After' determining the various attributes of these two principal constituents, the properties of the lamina were calculated by the micromechanical approach. A 5-axis filament winder machine was constructed in this research to manufacture the CNG tank.3D thermo-mechanical analysis was conducted by ANSYS-12 based on the micromcchanical outputs for 50, 55 and 60 percent of fiber volume fractions. Results showed that increasing the number of layers and the fiber volume fraction have opposite effects on the behavior of laminate and the metal liner failure. It was also found the significant effects of thermal stresses on the laminate failure, while their effects were ignorable on the metal liner failure.

In this investigation, effects of micro plasma arc welding variables (such as: welding current and pulsation), on the microstructure, mechanical properties, and electrical resistance of 80Ni-20Cr heating alloy have been studied. The 2 mm diameter wires were used as the base metal and welded at various conditions. The Optical Microscopy (OM), Scanning Electron Microscopy (SEM), tensile test, micro hardness test, and electrical resistance test were performed to evaluate microstructural, mechanical properties, and electrical resistance of the welds. The OM and SEM examinations show that weld metal in all samples had equi-axed grains. Grains and carbides size (Cr23C6 and TiC) both increased by increasing of welding current. The tensile and microhardness results showed, a decrease with increasing the grains size, and carbides size. In addition, at constant welding currents, with applying pulsation, higher tensile strength and hardness were obtained. The electrical resistance results showed, that electrical resistance of welded joints depends on the grains size and carbides distribution. The lowest electrical resistance was obtained at the welding current of l10 A in pulsation mode.

By considering the recently built Marvdasht city sewage network and the lack of industrial wastewater, it is expected that hydrogen sulfide gas will not form in the sewage network. But, improper slope, width of flow, pumping conditions, velocity of flow and temperature arc the- main reason to increase production of hydrogen sulfide gas. Based on the geographical location of the city in particular, microbial corrosion conditions in the network is provided the length of sewage network (14 km concrete pipes) and the lack of proper slope, caused the wastewater flow with some problems. Therefore, the use of pumping station for wastewater transmission is necessary otherwise. the wastewater detention time in the network will increase and the potential of velocity reduction as a result of growth of biofilm layer and emission of hydrogen sulfide gas will occure. In this paper, microbial- corrosion of wastewater concrete pipe in Marvdasht city by mesurment of hydrogen sulfide gas was investigated. The results show that the average concentration of hydrogen sulfide gas was 0.96 ppm, which is more than what is required Microbial pipe corrosion.