Year:2009 | Volume:43 | Issue:2 (120)|Papers Count:11

The effect of T6 heat treatment on the microstructure and wear behavior of Al-332 piston alloy containing 1.2wt% iron was investigated. The results showed that the T6 heat treatment changed the morphology of acicular eutectic Si particles to a more spherical form. The heat treatment also reduced the average length and blunted the needle-like b- phase intermetallics through dissolution and fragmentation. The results also showed that an increase in the time and temperature of the heat treatment decreased the length of the b -phase by about 70 percent and further blunted it at solutionizing temperature of 520oC for 14h. The results also showed that heat treatment increased the wear resistance of the alloy by about 40 percent.

There are no appreciable amounts of nickel resources in Iran, therefore, secondary resources of this element are to be more considered in future. Spent nickel catalysts that are used in various industrial processes are one of them. For example nickel catalyst that is used in hydrogenation of edible oil have large amounts of nickel and they are generally supported on porous materials like silica and alumina. Thus, economically extraction of nickel from these materials is an important subject. Hydrometallurgy is the common method for recovery of nickel by suitable leachant. In this work, different acids such as sulfuric, nitric and hydrochloric are used as the solvent for nickel recovery. The effect of some parameters on the recovery of nickel such as acid concentration, reaction time, temperature and oil existence were studied. The results obtained show that, by leaching spent nickel catalyst at high temperature with nitric acid, extraction of nickel is more than 90%. Furthermore, elimination of oil from spent catalyst with organic solvent increases the nickel extraction. The results of the kinetic analysis of the leaching data for various experimental conditions indicated that the reaction is controlled by diffusion through the catalyst network.

Al-SiC composites are among the most demanding metal matrix composites due to their excellent strength, good ductility, good corrosion resistance, low coefficient of thermal expansion and reasonable price. Manufacturing of cast metal matrix composites usually involves some problems such as inhomogeneous distribution of the particles due to poor wetability of ceramics to molten alloys, porosity and formation of particle-void clusters. Thus it seems necessary to utilize secondary processes for these materials in order to obtain suitable properties. In this research Al6061 composites reinforced with 10 volume percent SiC particles of 48μm average size were produced by the stir casting method and effect of extrusion process on the microstructure and strength of these materials was investigated. Results showed that the average particle size and porosity of the composite samples decreased after extrusion. Moreover, tensile strength of the composite increased by increasing the extrusion temperature and/or the extrusion ratio since the pores in the microstructure diminished and the interface bonding was improved.

In this study, Aluminium2024- Graphite composites containing 5, 10, 15 and 20 weight percent of graphite were produced by solid assisted melt disintegration (SAMD) technique which resulted in production of Al/Gr powder mixtures which subsequently consolidated and sintered for preparation of Al/Gr composites. In this technique, powder mixture was prepared by addition of flake graphite (mean diameter 55 μm) to the molten 2024 aluminum alloy. The slurry was stirred at a specified time-temperature cycle before air-cooling. For determining the optimum processing conditions, four time-temperature cycles were used. In these cycles the Al 2024 alloy was stirred in liquid and/or semisolid conditions in the presence of graphite powder. The screen test as well as laser particle size analysis demonstrated a wide size distribution of the resultant Al/Gr powder mixture. The graphite content of the powder mixture in different size ranges quantified by chemical dissolution method exhibited a higher percentage for smaller size bands. SEM studies confirmed the attachment of some graphite particles to the coarse aluminum powders Powder mixtures with different graphite contents (0-20wt%) were compressed uniaxially at optimum pressure. The compacted samples were sintered at suitable temperature. Fracture surface of compressed and sintered samples were studied by SEM. It was concluded that with using the optimum time-temperature cycle, the time of process decreases and the yield of produced powders increases. Powder mixtures produced by this method exhibited a wide size distribution. SEM studies confirmed that the graphite flakes were adhered to the surface of coarse Al powder particles while in the smaller size bands a mixture of free graphite flakes and Al powders could be observed. The SEM studies on the fracture surface of Al/Gr composites produced by the present method confirmed a relatively uniform distribution of the graphite particles in the matrix alloy.

In this study, Al/Gr composites with 5,10,15,20 weight percent of graphite were produced by in-situ powder metallurgy method. The produced powder mixtures were consolidated and sintered at optimum conditions. The resultant composites were solution treated at 495oC and aged at 170oC. The influence of graphite content on the bending strength of composites was studied. The distribution of graphite in the composite fractured surfaces was studied by SEM. It was concluded that the graphite particles were uniformly distributed in the matrix alloy. The maximum hardness could be achieved by aging at 170oC for 5h and this time was independent on the content of graphite. The increased graphite content decreased the bending strength of the composite.

This study mainly concentrates on metallurgical structure of the ferrous ancient crafts, specially the discovered ferrous man-made pieces in Ilam which are aged more than 3000 years. The pieces were discovered in Ize a town located in the south east of Ahvaz, in the southern of Iran. The crafts include an ferrous bar, a 3-side and a 4 side bayonets which were microscopically studied by Electron and Optical Microscopes. The Microscopic result shows that the main microstructure of the ironic crafts are ferritic with a minor pearlite which means the main composition of the crafts is low carbon iron. This finding was also confirmed by chemical analysis of the craft. In addition, a few micro-impurities were detected in the microstructures which were characterized as Slags. The slags were supposedly constrained in the crafts during hot forging process. Although the slags had different morphologies their compositions were iron oxides.

Vanadium is distributed widely and scarcely (150 ppm) on the earth. Its major applications are in steelmaking, dye-production and catalyst-fabrication industries. With the ever-increasing demand for this metal, secondary resource-exploitation of such waste materials as spent catalysts is recommended. Many reactions are involved in vanadium-extraction from these resources. Since roasting in comparison with other reactions is too slow, its investigation is crucial for vanadium revitalization. This paper focuses on sodium-carbonate roasting of vanadium oxide and brings about both process kinetics and the governing rate equations. Experiments are carried out at isothermal conditions with different molar ratios of vanadium oxide to sodium carbonate species (1:1, 3:1 and 6:1). Prevailing mechanism and the activation energies of the roasting steps are determined by application of shrinking core model to the pertaining two-phase reaction.

The present article considers the Nd:YAG pulsed laser welding of 304 stainless steels with two different compositions. The effects of various laser operational parameters and cooling rates on the weld microstructures were considered. The results show that ferritic solidification is produced in the stainless steel with the Creq/Nieq ratio of 1.7, and austenitic solidification is produced in the stainless steel with the Creq/Nieq ratio of 1.61. Moreover, the study shows that by using a high laser power, at high cooling rate, more ferrite is produced in the stainless steel welds. For the 1.7 Creq/Nieq ratio of stainless steel, the amount of ferrite is increased by using high laser power. In addition, high power laser produced more ferrite in the weld interface of 1.6 Creq/Nieq ratio of stainless steel. Samples were also undergone, proof and burst tests and the fracture surfaces were considered. The fractographic examinations show that the mechanism of the fracture was ductile fracture, and the defects such as porosity, low weld depth may help in producing the fracture of the sample.

In this research, the effect of friction between the liquid metal and the sand mould wall and the effect of passage of liquid through a vertical bend and through a ceramic filter on the fluid flow and the melt velocity has been studied by measuring the velocity of the melt and direct observation of the liquid flow through the different parts of a naturally-pressurized running system. The friction factor was calculated using the experimental results and it was shown that the friction had a significant effect on the reduction of the melt velocity. The effect of passage of liquid through a vertical bend was measured to be 20% and a filter was estimated to reduce the liquid metal velocity by half (almost half of the effect that was stated in the literature). The design of the running system was slightly altered considering the obtained effect of filter on the melt velocity. The comparison of reliability of the castings obtained by different running systems, using a Weibull statistical method, showed that the altered naturally-pressurized running system produced the most reliable castings and that the effect of the new method of running system design was greater than that of the use of a ceramic filter in the common unpressurized running system.