نشریه مهندسی متالورژی و مواد
سال سی و یکم شماره 1 (پاییز و زمستان 1398)

In this study a super high-strength Al-Zn-Mg-Cu alloy was rheo- extruded by a co-rotating twin-screw extruder with different solid fractions and rotation speeds. Nominal composition of Al-14Zn-9Mg-5.2Cu and process temperature interval was thermodynamically determined. FESEM and optical microscopes were used to investigate micro structural features. Optimized combination of strength and ductility was obtained at 0.6 solid fraction and 450 rpm for screws. The mechanical properties of the rheo- extruded samples at these conditions were: UTS of 682, 621MPa 0.2% proof stress and 10% elongation.

In this research, Ni-Cu/Al2O3 composite coatings were prepared by electrodeposition from a citrate-ammonia bath; and the effect of deposition current density on the microstructure, hardness and electrochemical corrosion behaviors of the coatings was studied. The results showed that the morphology and composition of the coatings are changed with the current density. Also, by increasing the current density, the microhardness of the coatings is enhanced and then decreased; whereas the corrosion resistance of the prepared coatings is progressively decreased.

The key issue in the processing composite material is to create an appropriate distribution of the secondary phase and make an adhesive interface. In this research, the effect of surface treatment of glass fibers on the mechanical behavior of composites with epoxy matrix has been investigated. EP 2040/2047 epoxy as the matrix and E-glass as the secondary phase has been employed. Similarly, an amino silane as a coupling agent has been used. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of glass fibers was performed using a 10% (v/v) hydrochloric acid. Surface modification evaluated by using Fourier Transform Infrared spectroscopy. Composite samples were constructed by Vacuum Infusion Process method and short beam shear test has been conducted to determine the performance of the acid treatment and the silane treatment in terms of the interlaminar shear strength. The silane coating glass fibers increased 18% the shear strength of the composite. However, the silane coating on the acid activated glass fibers did not improve the shear strength of the composite.

In this research, the effective parameters on the oxidation of ZrB2 ceramics were investigated. Temperature, time and pressure in addition of different additives (SiC, Cf, MoSi2, HfB2 and ZrC) were investigated. Taguchi method was applied for experimental design. Oxidation test was conducted on box furnace at 1600 C for one hour. It was cleared that the HfB2 resulted to better oxidation resistance. At the presence of ZrC, oxidation resistance was damaged. SiC improves the oxidation resistance by borosilicate layer formation. Finally, among the SPS parameters, temperature is the most.

Mostly, the physical properties of iron ore particles such as wettability, size, size distribution and morphology have important effects on the pellet ability of powder mixtures and quality of green pellet. In this work, these physical properties of particles used in the pelletizing plant of Mobarakeh Steel Co. were studied. The wettability of iron ore particles was evaluated using different wetting media and the samples which were prepared from lumps of low and high purity iron ores (received from Chadormalu and Sangan). The scanning electron microscope, laser diffraction particle sizing measurement (SLS method) and sieve screening experiments were used to evaluate the shape, size and size distribution of particles. The BET and Fisher tests were employed to determine the pore distribution and specific surface area, respectively. The high wettability was measured for high-grade Chadormalu iron ore when Carboxymethyl cellulose organic binder solution was used. The results also showed that the NaOH addition reduces the wettability of iron ore. The average particle size of milled concentrate in the mixed materials was measured around 10 . The small particle sizes facilitate the formation of micro-agglomerates in powder and the consequent reduction of capillary pressure during the pellet forming. The results of BET experiment also revealed the reduction in porosity and roughness of particles surfaces.

In this work, the effects of addition of 2 wt. % Cu and 2 wt. % P on the porosity percent, microstructure, and mechanical properties of 0.5 wt. % C steel foams manufactured by powder metallurgy through urea granulates as space holder were separately investigated. After manufacturing steel foams, determination of porosity percent by dimensional measurement, microstructural evaluation through optical and scanning electron microscopes, and investigation of mechanical behavior by compression test were conducted. The average of porosity percent in steel foams with Cu and P are 75 and 80 percent, respectively. In microscopic evaluations, two types of cells were observed that consisted of the solved urea cells and pores in the cells walls. In addition, the thickness of the cells walls was approximately measured from 90 to 102 micron. In the compressive stress vs. strain curves of Cu and P added steel foams, a long plateau region was observed. It is noteworthy that plateau region in the P added steel foams was as teeth-saw shape that related to the fracture of cells walls.

In present work effects of strain in hot working process and solution annealing, on microstructure and subsequent mechanical properties were investigated. The billet were hot rolled into final reduction in thickness 60 and 85% (R-60 and R-85) at 1150 ˚C. After that, solution annealing at 1140 ˚C to 1200 ˚C for 10 to 120 minutes were conducted to optimize of mechanical properties. The microstructures revealed grain size of R-85 sample was lower than another, but grain growth was observed for annealed sample above 1140 ˚C after 30 minutes. EDS analysis shown M6C carbide rich of tungsten is only precipitated carbide. It's also found that grain growth rate is much more for R-85 sample. SEM evaluations also confirmed faster solution rate of carbides for R-85 sample. Yield strength of R-85 is very higher relative to R-60 while after annealing at 1140 ˚C for 10 minutes it decreased drastically. Annealing in same condition for R-60 sample cause not only decreasing of strength, even improved ductility.

In this research, the effect of major welding parameters on microstructural evolutions and mechanical properties of double-sided friction stir welded thick 5083 aluminum alloy joints was investigated. For the traverse speed of 80 mm/min, the increase in the rotational speed does not have any effect on the average grain size. In this case, it can be said that the annealing grain growth and recrystallization effect counteract and neutralize each other. However, for the traverse speed of 40 mm/min, with increasing the rotational speed, the grain size increases due to the dominance of annealing grain growth effect. Grain size in the stir zone was decreased about ten time as compared with base metal; however, no considerable increase was observed in the hardness of the stir zone and the hardness profile remained almost uniform alongside the joint area. The best joint efficiency was equal to 99.4 % with the pin length of 6 mm and transverse and rotational speeds of 80 mm/min and 1000 rpm, respectively. Also, the elongation was improved about 9 % compared to the base metal.

The mode and rate of agitation of the particles is one of the effective variables for dissolving solid particles in the aqueous solution. In the present study, a computer software has been used for simulation of the particle agitation in the pilot mixer reactor. The stirrer speed, pulp density, particle size and solid particles density were selected variables. The effect of above factors on velocity of particles and their accumulation was investigated. The stirrer speed has significant effect on the particle velocity, but by increasing the pulp density, average speed of the particles is more limited. Increasing the size and density of particles can reduce the speed of moving parts. Particle accumulation has increased with increasing pulp density and particle size. The stirrer speed significantly decreases the amount of inactive areas in the reactor. The density of particles does not effect on particle accumulation.

Manganese problems in the Solvent extraction-Electrowinning Circuit occur when manganese from the solvent extraction stage into the electrowinning stage can be found. In the electrowinning stage, due to the availability of oxidation conditions, oxidation of manganese is oxidized to 7 valences positive capacity. By increasing the soluble Eh, in addition to causing corrosion conditions in the electrowinning cell, contact with the organic phase leads to the destruction of the organic phase, which results in the formation of a crud in the settlers. The ways in which this impurity moves to the electrowinning stage involves chemical transfer by forming a complex or physical transfer through aqueous entrainment. In this study, the manganese transfer rate was studied by these two methods. As a result of these studies, it was found that the amount of manganese transfer through the chemical is very small and is 0.065 mg /l, and compared with the transfer of manganese through aqueous entrainment, it is about 4 times higher and 0.28 mg/l. In addition to the two routes of manganese transmission, it was found that crud also played a role in the transfer of manganese. The amount of manganese transfer through crud was 20 mg/l. According to these results, crud contribution to the manganese transfer has been greater, which reduces the crud in the system, preventing the effects of manganese in the circuit.

The aim of this study is to achieve a monophasic mullite (3????????2????3.2????????????2), with stoichiometric ratio of (3:2) and non-stoichiometric ratios of (2: 1) and (3: 4) by sol-gel method. Tetraethylorthosilicate (TEOS) and aluminum nitrate nonahydrate (ANN) were used as main ingredients. After gelation process, all the samples were aged at ambient temperature for 17 days and then dried at two different temperatures. All prepared samples were heat treated at temperatures ranging from 600-1550 °C and cooled in the furnace. Heat treated samples were characterized with XRD analysis to identify the crystalline phases. SEM and FTIR analysis were also performed to evaluate the morphology and chemical configuration of crystalline phases, respectively. In stoichiometric samples and non-stoichiometric specimens with higher alumina content, the needle morphology of mullite were observed.

In this study butt joining of 7020-T6 alloy was performed using tungsten inert gas (TIG) welding with continuous (constant) and pulsed current. Effect of heat input on microstructure and mechanical properties of the joints was investigated. Microstructural examinations were conducted using optical and scanning electron microscopy. Differential scanning calorimetry (DSC) was used to identify the precipitates phase evolution. Temperature at the welding region was recorded by inserting thermocouples. Hardness and tensile strength of the joints was evaluated. Results showed that current pulsing leads to relatively finer grain size in weld metal compare to the one welded by constant current. In either cases of constant and pulsed current, the grain size and the width of heat affected zone increased with increasing heat input. Unlike earlier studies in precipitation hardening aluminum alloys, strength of the weld metal were increased as compare to base metal in T6 condition. The enhancement in mechanical properties of weld metal was attributed to the solution annealing and re-formation of strengthening precipitates on cooling from welding temperature.