Iranian Journal of Materials Science and Engineering

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Metal porous foams have been eliciting much interest in recent years due to their high capacity of energy absorption. The characteristics of the pores in these materials play an important role on their energy absorption capability and other properties. This study reports the fabrication of aluminum closed-cell foams by accumulative roll-bonding (ARB) technique using calcium carbonate (CaCO3) as the blowing agent. Calcium carbonate is an inexpensive material and imparts relatively high porosity to the produced foam. The effects of heating rate foaming temperature and time on porosity have been investigated. The results show that increasing the foaming temperature and time results in improvements in the foaming process. It is also shown that the heating rate does not affect the porosity. The shape and structure of pores are spherical and regular with CaCO3 as blowing agent. With TiH2 blowing agent the sample should be heated up abruptly from decomposition temperature of TiH2 to foaming temperatures in order to produce high porosity foam. It is found that increasing the numbers of accumulative rolling cycle causes uniform distribution of calcium carbonate powder and increases porosity in the final foam by up to 55%.

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The probable reasons for evolution of weld porosity and solidification cracking and the structure- property relationship in aluminium welds were investigated. Aluminium plates (1xxx series) were welded by Tungsten Inert Gas (TIG) welding process, 5356 filler metal was used and heat input was controlled by varying welding current (145A, 175A and 195A). The welded samples were examined under optical and scanning electron microscopes and mechanical tests were performed to determine tensile and impact strengths. Secondary phase, identified as globules of Mg2Al3 precipitates, was found to be formed. Solidification cracking appeared in the heat affected zone (HAZ) and porosities were found at the weld portion. The tendency for the formation of solidification cracking and weld porosities decreased with increased welding current.

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trontium hexaferrite (SrFe 12 O 19 ) nanosized powders were synthesized by sol-gel auto-combustion method with and without cetyltrimethylammonium boromide (CTAB) addition in the sol with Fe/Sr ratio of 11 (using additional Sr). The resultant powders were investigated by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM) and Vibration Sample Magnetometer (VSM) techniques. Phase constituents of the synthesized samples which were heat treated at temperatures in the range of 700- 900 ◦C were studied. XRD results revealed that CTAB addition facilitates the formation of single phase strontium hexaferrite at 800 ◦C. Microstructural evaluations with FESEM represented that CTAB addition causes formation of larger particles with a narrower size distribution. VSM results represented that the highest amount of intrinsic coercivity force ( i H C ) was obtained in the sample without CTAB addition and with additional Sr, calcined at 800 ◦C for 1 h which was equal to 5749.21 Oe, while the value of i H C was equal to 4950.89 Oe without additional Sr. The amount of maximum magnetization (M max ) was raised from 48.41 emu/g to 62.60 emu/g using CTAB and additional Sr. The microstructure and magnetic properties of the samples have been explained

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Effect of electro migration on crystal structures of platinum nanowire (Nano bridge) during Nano-gap formation is investigated by means of Transmission Electron Microscopy (TEM). Selected area diffraction patterns as well as bright field images are used for this investigation. There were severely recessions in the polycrystalline Nano bridge and crystal structures around the nanogap changed completely during electro migration. Due to Joule heating, original small crystal with random orientation disappeared and newly crystals with a preferred orientation grew. They have [111] orientations (respect to beam direction) with slight misorientations. α and θ was defined to calculate the misorientation and used to represent Nano-gap formation mechanism. The calculation gives the breaking of Nano bridge occurred along grain boundaries in most of Nano bridges. The controlling system during eletromigration may affect on the shapes of tips so that the shape of tips in Nano bridges, in which feedback control is applied, is more symmetric than others. The effect of temperature on atomic diffusivity might be the reason of the behaviour. {422} could be a preferred surface plane for mass transport in platinum Nano bridge in which atoms move along it

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On time replacement of a cutting tool with a new one is an important task in Flexible Manufacturing Systems (FMS). A fuzzy logic-based approach was used in the present study to predict and simulate the tool wear progress in turning operation. Cutting parameters and cutting forces were considered as the input and the wear rate was regarded as the output data in the fuzzy logic for constructing the system. Flank wear was used as the tool life criterion and the wear ranges were selected between 0 and 0, 3 based on ISO 3685 standard for new and worn tool respectively. For conducting the tests, Taghuchi method was used to design an experimental table. The results of the measurements and estimates confirmed the reliability of the fuzzy logic method for estimating tool wear. One significant feature of the proposed system is that it can predict the wear rate on-line by transferring the cutting force signals from the sensor to the fuzzy logic simulation box.

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Compression springs were prepared from Cr-Si high strength spring steel and coated with pure Zn and ZnNi by electroplating process. The effect of baking after electroplating as well as applying an electroless nickel interlayer on the fatigue and fatigue corrosion of the springs was investigated. The results were analyzed using weibull statistical model. A considerable improvement (8%) in fatigue life of the electroplated springs with Zn-Ni was observed in the presence of Ni interlayer. In addition, baking of these electroplated springs improved fatigue life by 4%. The fatigue life under salt spraying conditions, however, has demonstrated remarkable reduction by 40%, 34% and 30% for Zn-Ni plating, backed and unbaked Zn-Ni plating containing Ni interlayer, respectively

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In the present study, the feasibility of α-Fe ferromagnetic phase formation in glass and glass-ceramic by reduction in hydrogen atmosphere have been investigated. The glass with the composition of 35Na 2 O–24Fe2O3–20B 2O3 – 20SiO 2 –1ZnO (mol %) was melted and quenched by using a twin roller technique. As quenched glass flakes were heat treated in the range of 400-675 °C for 1-2 h in hydrogen atmosphere, which resulted in reduction of iron cations to α-Fe and FeO. The reduction of iron cations in glass was not completely occurred. Saturation magnetization of these samples was 8-37 emu g -1 . For the formation of glass ceramic, As quenched glass flakes heat treated at 590 °C for 1 h. Heat treatment of glass ceramic containing magnetite at 675°C in hydrogen atmosphere for 1 h led to reduction of almost all of the iron cations to α-Fe. Saturation magnetization of this sample increased from 19.8 emu g -1 for glass ceramic to 67 emu g -1

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In this paper, the effect of MgO, BaO, Na 2 O and SrO addition to a pre-melted CaO-Al2O3 -Si 2 O synthetic slag on sulfur removal from plain carbon steel was studied under the same experimental conditions. The slags were pre-melted at 1400°C in an electric resistant furnace and desulfurization experiments were carried out in a high frequency induction furnace. The results showed that the optimum reaction time for desulfurization was 15 min. It was found that while SrO addition to the ternary slag enhances the sulfur removal capability, MgO, Na 2O and BaO additions reduce desulfurization efficiency of the ternary slag. Moreover, it was observed that restricting access to oxygen from the atmosphere by using a covered crucible, could increase desulfurization efficiency of the slag by more than two fold

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In this study, Al2014 alloy refined with Al-5%Ti-1%B master alloy was prepared by strain-induced melt activated (SIMA) process. The main variables of the SIMA process were cold working, holding time and temperature in semi-solid state. Cold working was applied on specimens by upsetting technique to achieve 10%, 20% and 30% height reduction. Cold worked specimens were heat treated in semi-solid state at 585 °C, 595 °C, 605 °C, 615 °C, 625 °C and 635 °C and were kept in these temperatures for different times (20 and 30 min). Observations through optical and scanning electron microscopy were used to study the microstructural evaluation. The results revealed that fine and globular microstructures are obtained by applying 30 % height reduction percentage and heat treating in 625 °C for 30 min. Comparison between refined and unrefined Al2014 alloy after applying SIMA process showed that Al-5%Ti-1%B master alloy has no significant effect on average globule size but makes the final structure more globular.

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The volatile matter of non-coking coal was used for the reduction of hematite in argon atmosphere at nonisothermal condition. A thermal gravimeter furnace enable to use an 80 mm-height crucible was designed for the experiments to measure the weight changes of about 10 grams samples. A two-layered array of coal and alumina and four-layered array of iron oxide, alumina, coal and alumina was used for the devolatilization and reduction experiments, respectively. The net effect of volatile reduction of Fe 2O3was determined and it was observe that 45% reduction has been achieved. Three distinct regions were recognized on the reduction curve. The reduction of hematite to magnetite could be completely distinguished from the two other regions on the reduction curve. At 600-950°C, the reduction was accelerated. 63% of volatile matter resulted in 25% of total reduction before 600°C while the remaining volatile matter contributed to 75% of the total reduction. From the reduction rate diagram, the stepwise reduction of the iron oxides could be concluded. The partial overlap of the reduction steps were identified through the XRD studies. The starting temperature of magnetite and wüstite reduction were determined at about 585°C and at 810°C, respectively.

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MgAl2O4/Ti(C,N) composites were synthesized through aluminothermic reaction between Al,TiO 2,MgO powders and phenolic resin in coke bed condition. Effect of addition of carbon black and sugar into the mixture at different temperatures were investigated. The phases and microstructures of samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). MgAl 2O4 /Ti(C,N) composites without additive were obtained after heat treatment at 1600˚C. With addition of carbon black TiC, TiN and Ti(C,N) were appeared after firing at 1400˚C and formation of spinel/Ti(C,N) composites were completed at 1600˚C. In sample containing sugar, MgAl2O4 -Ti(C,N) composite were completely synthesized at 1400˚C. In this sample crystallite size of Ti(C,N) were 32 nm and carbon content of titanium carbonitride (Ti(C,N)) reached to 0.442 value.

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Precipitation hardening is the most common method in the strengthening of aluminium alloys. This method relies on the decrease of solid solubility with temperature reduction to produce fine precipitations which impede the movement of dislocations. The quality control of aluminium alloy specimens is an important concern of engineers. Among different methods, non-destructive techniques are the fastest, cheapest and able to be used for all of parts in a production line. To assess the ability of eddy current as a non-destructive method in the evaluation of precipitation hardening of aluminium alloys, 7075 aluminium alloy specimens were solution treated at 480°C for 1 hr. and followed by water quenching. Afterwards, the specimens were aged at different temperatures of 200, 170, 140, 110 and 80°C for 8 hr. Eddy current measurements was conducted on the aged specimens. Hardness measurement and tensile test were employed to investigate the mechanical properties. It was demonstrated that eddy current is effectively able to separate the specimens with different aging degree due to the change of electrical conductivity during aging process

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Hot dip aluminizing was carried out on the low carbon steel rod under optimized conditions. The aluminized samples were further oxidized at 1000̊C in air atmosphere at two different times of 20 and 60 minutes. Microstructure study and phase analysis were studied by scanning electron microscopy and X-ray diffraction methods, respectively. The characterization of the coating showed that, Fe2 Al5 has been the major phase formed on the surface of specimen before heat treatment. Following the oxidation of the coating at high temperature, Al 2O3 was formed on the surface of coating while Fe 2 Al5 transformed into FeAl and Fe 3 Al which are favorable to the hot corrosion resistance of the coating. Corrosion resistance of aluminized samples before and after heat treatment was evaluated by rotating the samples in the molten aluminum at 700 ̊C for various times and the dissolution rate was determined. The obtained results showed that by oxidizing the coating at high temperature, the corrosion resistance of the samples in molten aluminum improves significantly.

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Creep age forming (CAF) is one of the novel methods in aerospace industry that has been used to manufacture components of panels with improved mechanical properties and reduced fabrication cost. CAF is a combined age-hardening and stress-relaxation that are responsible for strengthening and forming, respectively. This paper deals with the experimental investigations of mechanical and springback properties of Al-Zn-Mg Al alloy in creep forming process. Creep forming experiments have been performed at temperatures of 120◦C and 180◦C for 6–72 h. Results indicated that yield stress and hardness of creep age formed specimens increased with increasing forming time and temperature,  simultaneously induced deflection by stress-relaxation increased. Incorporating spring back and mechanical properties, it can be found that the appropriate forming cycle was 180 ◦C/24 h among all forming conditions. CAF Time increase to a certain extent increased mechanical properties. This can be attributed to presence of stress in CAF that causes the precipitates be finer because of creation more nucleation sites. Therefor the growth of precipitates, takes place at long time and postpones the decreasing of the yield stress

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 Microsegregation is one of the most important phenomena occurs during solidification. It usually results in formation of some unexpected second phases which generally affect the mechanical properties and specially reduce the workability of casting products. The aim of this research is to study the effect of cooling rate and grain refinement on the microsegregation in Al-4.8 wt.% Cu. For this purpose two series of experiments were designed. In the first set of experiments, the alloy was melted and cooled in three different rates, i.e. 0.04, 0.42, and 1.08 K/s in a DTA furnace. In the second series of experiments, the effect of grain refinement on the microsegregation at a constant cooling rate of 0.19 K/s was investigated. Al-5Ti-1B master alloy was used as grain refiner. Results showed that by increasing the cooling rate the amount of non-equilibrium eutectic phase increases from 5.1 to 7.4 wt.%, and the minimum concentration of solute element in primary phase decreases from 1.51 to 1.05 wt.% Cu. By grain refinement of the alloy, the amount of non-equilibrium eutectic phase decreases from 5.5 to 4.7 wt.%, and the minimum concentration of solute element in the primary phase increases from 0.98 to 1.07 wt.% Cu. So it is concluded that increasing cooling rate in the range of 0.04 to 1.08 K/s, increases and grain refinement reduces the microsegregation 

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Equal-channel angular pressing (ECAP) combined with the Conform process provides a solution for the continuous production of ultrafine-grained materials. In the present study finite element method was executed to investigate the effects of die channel angle and friction on the strain homogeneity and the required torque in ECAP-Conform process. Deformation behaviour of Al 6061 wires was analyzed by using the ABAQUS/Explicit software. Finite element analyses by considering different channel angles (90ᵒ, 100ᵒ and 110ᵒ) and various friction conditions of 0.2, 0.3 and 0.4 were surveyed. The results revealed two distinct trends in which by increasing the channel angle among 90ᵒ to 110ᵒ, the amount of induced plastic strain through the wire reduced about 40%. Also required processing torque was decreased about50%. In addition more homogeneity was observed in higher angle values. The results regarding to equivalent strain, obtained from FE analyses, showed a good agreement with previous studies. Eventually plastic strains and required torque were increased about 8% and 12% when friction coefficient raised between (0.2-0.4).

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The purpose of this research is to achieve the optimal parameters for producing forged aluminium alloy 7075 aircraft door bracket by using finite element modelling (FEM) with commercial DEFORM-3D V6.1 and physical simulations with plasticine and Plexiglas dies. Also, forging speed has been examined as the main factor for controlling to produce a part without any defects. The results of Physical Simulation showed that the flow pattern has good agreement with the results of FEM that based on the use of hydraulic presses with initial billet and dies temperatures 410 and 400 ° C, respectively, and different forging speeds 5, 10 and 15 mm/sec. Distribution of effective strain rate, effective strain, effective stress, temperature , forging force and dies­ wear showed improvement the results in forging speed of 5 mm/sec. Processing map of Aluminium alloy 7075 also checked out at constant strain 0.5, indicated that the specified area of the forged part is located in a safe area. Forging force in optimized forging speed 5 mm/sec showed that the forging process using a 1000-ton press can be done easily

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Because the partition coefficient is one of the most important parameters affecting microsegregation, the aim of this research is to experimentally analyse the partition coefficient in Al-Mg alloys. In order to experimentally measure the partition coefficient, a series of quenching experiments during solidification were carried out. For this purpose binary Al-Mg alloys containing 6.7 and 10.2 wt-% Mg were melted and solidified in a DTA furnace capable of quenching samples during solidification. Cooling rates of 0.5 and 5 K/min were used and samples were quenched from predetermined temperatures during solidification. The fractions and compositions of the phases were measured by quantitative metallography and SEM/EDX analyses, respectively. These results were used to measure the experimental partition coefficients. The resultant partition coefficients were used to model the concentration profile in the primary phase and the results were compared with equilibrium calculations and experimental profiles. The results of calculations based on the experimental partition coefficients show better consistency with experimental concentration profiles than the equilibrium calculations.

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High speed and absence of a precise control over pressure distribution confine sheet Electromagnetic Forming into a die to simple shapes having shallow depth. It is possible to reach a higher depth by using a convex punch instead of a concave die. In this study, sheet Electromagnetic Forming on a punch and sheet Electromagnetic Forming into a die are investigated. The electromagnetic part of the study is investigated analytically and its mechanical part is studied numerically. In order to couple electromagnetic with mechanical parts, no-coupling method is used. The obtained results are verified by comparing the obtained results with previous experimental ones in literature. Rate-dependent and rate-independent hardenings are taken into consideration for the mechanical behavior for material of AAl1050. Using appropriate hardening model for material yields acceptable results. Moreover, a convex punch instead of a concave die is used to reach to a higher depth in sheet Electromagnetic Forming.

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Till now, different constitutive models have been applied to model the hot deformation flow curves of different materials. In this research, the hot deformation flow stress of API X65 pipeline steel was modeled using the power law equation with strain dependent constants. The results was compared with the results of the other previously examined constitutive equations including the Arrhenius equation, the equation with the peak stress, peak strain and four constants and the equation developed based on a power function of Zener-Hollomon parameter and a third order polynomial function of strain power a constant number. Root mean square error (RMSE) criterion was used to assess the performance of the understudied models. It was observed that the power law equation with strain dependent constants has a better performance (lower RMSE) than that of the other understudied constitutive equations except for the equation with the peak stress, peak strain and four constants. The overall results can be used for the mathematical simulation of hot deformation processes