hamed jamshidi aval

In this research, the effect of heating rate on non-isothermal aging behavior of AA2024 aluminum ‎alloy matrix composite reinforced with nickel aluminide has been studied. Nickel aluminide was ‎created in-situ in the AA2024 aluminum alloy matrix and as a result of adding 4.5 wt.% of nickel ‎during composite fabrication. The results showed that the addition of nickel reduces the ‎precipitation ability of the AA2024 aluminum alloy during non-isothermal heat treatment despite ‎the formation of nickel aluminide. Also, with the increase of the heating rate, the amount of S-‎Al2CuMg precipitates formed in the microstructure decreases during non-isothermal aging. By ‎increasing the heating rate, the maximum hardness is reduced during aging heat treatment and is ‎obtained at higher temperatures. Non-isothermal aging of AA2024 aluminum alloy matrix ‎composite reinforced with nickel aluminide at a heating rate of 5°C/min led to an increase in ‎hardness and ultimate tensile strength by 17 and 22%, respectively, compared to the AA2024 ‎aluminum alloy matrix.‎

Aluminum alloys have good anti-corrosion properties and strength to weight ratio. In this paper, a statistical method based on finite element simulation was used to obtain the highest percentage of mold filling and the minimum percentage of thinning in the forming area. First, the finite element model is prepared and the accuracy is compared with the results of the experimental part. Effective factors including, temperature, pressure, pressure rate, axial feed and punch speed were evaluated by the response surface method in order to extract the model and find the maximum effect. Design Expert software was used to model the response surface methodology and Abacus finite element software was used to simulate it. According to the obtained results, the optimal points obtained for both characteristics are: temperature 552°C, pressure 6.5 bar, bar rate 0.02 bar/s, axial feed 7 mm and feed rate 0.05 mm /s with filling percentage 91.2 and a thinning percentage of 10.37 were obtained. The proposed model for predicting the values of variables had very close results with the experimental findings.

In the current research, the effect of strain path by two processes of conventional asymmetric rolling and asymmetric cross rolling, as well as natural aging on the microstructure and hardness of AA7075 aluminum alloy was investigated. The microstructure was examined by light microscopy and the hardness by macro-Vickers hardness tester. The results showed that the rolled sample (initial sample) had elongated grains due to rolling and the average width of the grains in this sample was 13.4 μm. By applying conventional asymmetric rolling up to 60%, the grains became more elongated and the average grain width reached 2.6 μm. By performing asymmetric cross rolling up to 40%, the average grain width reached 3.7 μm. The distribution of particles did not change significantly with rolling deformation. Shear bands were also formed in the sample after 40% and 60% conventional asymmetric rolling, as well as after 40% asymmetric cross rolling. At zero aging time, the hardness of the 60% conventionally rolled sample was higher than the 40% cross rolled sample. With increasing the aging time, the hardness of all samples increased due to natural aging. As the thickness reduction percentage increased (increasing the strain), the hardness increase percentage due to natural aging decreased. The increase in hardness due to natural aging was more noticeable in the cross-rolling process than in the conventional rolling process. After 7 days of natural aging, the hardness of the material reached its saturation limit.

Conventional methods of composite production using friction stir processing are simple, rapid, and economical. However, homogenizing the reinforcing particles in the processing zone is very difficult. In addition, this method mainly focuses on surface composite production, while obtaining bulk composites is still challenging. This study investigates the production of AA3105-SiC aluminum matrix composite using the sandwich method as the manufacturing process. The SiC particles were applied through spraying as a layer between AA3105 aluminum sheets. Then, the effect of friction stir processing parameters is investigated. The results indicate an enhanced degree of stirring and plastic deformation following increasing the rotational to translational speed ratio (w / v), which leads to homogenization of the particle distribution in the aluminum matrix. By increasing the w / v ratio, the distribution coefficient decreases from 0.58 to 0.21, which indicates an improvement in the distribution of particles in the matrix. The friction stir processing using the sandwich method significantly improves the mechanical properties of the AA3105-SiC bulk composite compared with the processed samples without reinforcement, with a maximum increase of 192 % in ultimate tensile strength and 273 % in toughness at 1600 rpm and 31.5 mm/min.

In the present study, using a new method, dual-phase (DP) steel with high strength and good ductility was produced from plain carbon steel with 0.16% carbon. The DP steel with ferritemartensite structure was obtained using austenitizing, quenching, asymmetric cold rolling, and intercritical annealing at temperatures of 770 and 800 °C and short holding times of 1 and 5 min. Due to the application of uniform shear strain through asymmetric cold rolling, a uniform distribution of the martensite phase was observed in the RD-TD and RD-ND planes. By increasing the holding time, the volume fraction of martensite increased from 8% to 12% at 770 °C and from 10% to 33% at 800 °C for the holding times of 1 and 5 min, respectively. Hardness and strength improved with increasing temperature and time of intercritical annealing. The sample produced at a temperature of 800 °C and a time of 5 minutes showed excellent mechanical properties such as 244 HV hardness and 1020 MPa strength and 12.5% ductility. In addition, due to the high volume fraction of martensite and the consequent reduction of its carbon content, the hardness of this phase decreased and as a result, it showed significant plastic deformation and high strain hardening. The fracture surface of all produced DP steels mainly included dimples, which indicates ductile fracture behavior.

In this paper, the manufacturing of a cylindrical AA6063 step tube via hot metal gas forming (HMGF) process is studied both experimentally and numerically. The goal is to investigate the effect of loading rate on the specimen profile and thickness distribution. ABAQUS finite element software is used for the numerical simulation. Experiments were carried out at 580°C in two conditions; first, without axial feeding and then with an axial feeding of 14 mm at a maximum pressure of 0.5 MPa. The studied parameters are the pressure rate and the axial feeding rate. The results show that in the non-axial feeding mode, the thickness distribution in the die cavity region was non-uniform and a rupture occurred at a pressure of 0.6 MPa. The reduction of the pressure rate has no significant effect on the rupture pressure. In the case of axial feeding, by choosing the pressure rate of 0.001 MPa/s and the axial feeding rate of 0.1 mm/s, wrinkling has been created in the specimens. However, at a pressure rate of 0.005 MPa/s and an axial feeding rate of 0.02 mm/s, the specimens are raptured. Under low pressure rate of 0.001 MPa/s and low axial feeding rate of 0.02 mm/s, the thickness in the die cavity area has decreased. A suitable die filling and thickness distribution are obtained at a pressure rate of 0.005 MPa/s and axial feeding rate of 0.1 mm/s.

To reduce corrosion, choosing proper coating for the outer surface of oil and gas transportation pipelines is considered the most important part in developing a protection system. The issue of cathodic disbondment is one of the problems of pipeline coatings which is caused by impressed cathodic current and generation of alkali environment at the coating-metal interface and result in coating disbondment. In this research, three coating types including, 3-layer polyethylene, polyurethane, and dual fusion bond epoxy powder are investigated and their physical, chemical, and mechanical properties are studied. The results of cathodic disbondment with simulating long-term working conditions provide an appropriate view on coatings behavior at long-term service exposure. Coating advantage in different properties such as surface adhesion to sublayer and impact resistance are investigated using mechanical tests results. Hardness test results showed that sample hardness with dual fusion bond epoxy powder coating compared to samples with polyurethane and 3-layer polyethylene coatings is 14% and 40% higher, respectively. Impact and holiday test on three coating also showed an acceptable level of resistance to external factors. Performing cathodic disbondment test at ambient and high temperature showed that increasing temperature has a direct influence on increasing coatings disbondment radius. 4.49 mm lowest disbondment radius was observed on 3-layer polyethylene coating due to its intrinsic nature and high thickness.

This study addressed the friction stir welding of AA2024-T351 and AA6061-T6 aluminum alloys with added reinforcing particles at 800 rpm, and a traverse speed of 31.5 mm/min. The specimens were heat-treated for different time durations to study the impact of SiC particles on aging kinetics during welding in different metallurgical regions. The Vickers micro-hardness and optical microscopy showed that the reinforcing particles enhanced aging kinetics and decreased the grain size in the stir zone. Moreover, compared to micro-sized SiC particles, the addition of SiC nanoparticles led to a higher hardness at the stir zone following the post-weld heat treatment. Although the joint containing SiC nanoparticles was associated with a higher strength after heat treatment, the trends of changes in strength with time were similar for all specimens with the maximum strength obtained after 20 hours of artificial aging at 160℃. The fracture was controlled by the weakest point of the joint which was located near the thermo-mechanically affected zone on the AA6061 side in all specimens. The mechanical behavior of the joint after heat treatment was identical to the stress-strain behavior of the AA6061 base metal.

In the present study, the mechanical and microstructural properties of dissimilar joint of 304 austenite stainless steel and C70600-copper-nickel alloy made by Gas Tungsten Arc Welding process has been investigated. The aim of this joint is using the twin metallurgical properties such as; heat dissipation and corrosion resistance of copper-nickel alloy and mechanical properties of 304 austenite stainless steel alloy. Welding of two dissimilar metal steel to copper-nickel alloy due to differences in melting point, the difference in thermal conductivity, rapid solidification of copper nickel are facing many problems. In this research due to solubility and weldability of nickel with two both alloys, three filler metals Inconel 625, Inconel 82 and 61 were used. According to microstructural investigations welds made by Inconel 625 and Inconel 82 show a finer equiaxed dendrite structure as compare as in Inconel 61 filler metal. The tensile strength of samples welded by Inconel 625, 82 and 61 filler metals was 324, 323 and 293 MPa, while the elongation percent of three samples show small difference. According to mechanical properties of joints, the Inconel 625 and 82 filler metal are appropriate for dissimilar welding 304 austenite stainless steel and C70600-copper-nickel alloy.

In the present study, microstructure and wear resistance of in-situ composite coatings TiC-Al2O3 and TiB2-TiC-Al2O3 product by gas tungsten arc welding process on AISI 304 austenite stainless steel were investigated. For this, a paste of the mixed powders of 3TiO2-4Al-3C and 3TiO2-4Al-B4C was provided and applied on the surface of AISI 304 austenite stainless steel substrate, then fused using gas tungsten arc welding process. The microstructural features and phase characterization of the cladded samples were investigated using optical and electron microscopy and X-ray diffraction analysis. The mechanical properties of clad layers were studied by Vickers microhardness and pin-on-disk wear tests. The microstructural investigations of cladded layers indicated that high heat input during welding led to high temperature synthesis and formation of significant reinforcing particles on the surface of steel. Also, the cubic TiC particles formed separately or inhomogeneously nucleated on Al2O3 particles in the austenitic matrix of 304 stainless steel. Likewise, the formation of TiB2 particles was approved with X-ray diffraction analysis. The rei

In this research, the friction-stir welding (FSW) process was used for butt joining of AA2024-T351 and AA6061-T6 dissimilar alloys. Welding was carried out using a tool with frustum of pyramid pin. The effects of rotational and linear speeds of the tool on microstructure, macrostructure, and mechanical properties of joints were examined. The AA2024 alloy was located in the advancing side due to higher flow stress at higher temperature than the AA6061 alloy, which was located in the retreating side. Macro analysis showed that with a rotational to linear speed ratio of higher than 31.25 revolutions per millimeter the transverse joint section demonstrated tunnel hole defect. With an increase in heat input material flow on different depth levels of joint became more homogenous and the AA2024 alloy’s amount in the stir zone increased. Moreover, with rotational to linear speed ratio of higher than 40 revolutions per millimeter, the effect of deformation rate was dominant, whereas with lower ratios the effect of temperature on grain size in the stir zone was dominant. Application of offset to the tool during welding in the retreating side led to improvement of flow of materials in the stir zone and an increase in friction stir joint strength.

Friction stir welding (FSW) has many advantages in welding dissimilar joints in comparison with fusion welding methods. In this study, weld ability of butt joint of 5052 aluminum alloy and Ti-6Al-4V titanium alloy by FSW process has been studied and discussed. The welding was successfully performed by using a tool with frustum pin. The influences of both rotational and traverse speed of welding tool on mechanical properties are investigated. The results show that the metallurgical and mechanical properties improve by choosing appropriate parameters. The highest tensile strength of 260 MPa was obtained at rotational speed of 500 rpm and a 40 mm/min traverse speed, which was ~ 94% of the aluminum base metal tensile strength. As a result of increasing the rotational speed from 500 to 1000 rpm, high heat input can forms cracks at joint area. In rotational speed of 1000 rpm, increasing traverse speed from 40 to 56 mm/min leads to a sound joint with 192 MPa of tensile strength. This decreasing in tensile strength can be related to the formation of intermetallic compounds such as TiAl3, along the entire interface between the two alloys

Due to the low formability of aluminum alloys at ambient temperature, forming of these alloys is performed at high temperature. Research has shown that the results of simple tensile test to predict the materials behavior at high temperatures are not sufficiently accurate to predict the formability of aluminum tubes at high temperature. The mechanical properties of the tube are very important at high temperatures. In this study the formability of 6063 aluminum alloy tubes are investigated by free bulging test at temperature range 430°C to 600°C. Then the mechanical properties including flow stress, strain rate sensitivity coefficient and strength constant are obtained using tube multi-bulge test at temperature range 530°C to 580°C. For this purpose, hot metal tube gas forming process is used and the effect of process parameters such as the effect of temperature, pressure and time on the expansion ratio and height of the bulge are studied. The results show that the maximum expansion ratio is 58% at 580°C. Bursting pressure decreases from 1.9MPa to 0.6MPa with temperature increasing from 430°C to 600°C. The bulge height increases with increasing forming time at constant pressure. Also with increasing temperature in the temperature range 530°C to 580°C the flow stress and strength constant decrease and strain rate sensitivity coefficient increases.

Metal bipolar plates are key components in fuel cells that are considered as the best alternative to replace graphite plates. Material selection in bipolar plates depends on its weight and corrosion resistance. Metallic bipolar plate can be considered as the best alternative instead of graphite and composite plates. One of the new processes in order to produce this plat is gas blow forming process. In this study, forming of AA8111 bipolar plates with 200 µm thickness in concave groove dies is investigated by gas blow forming process at various pressures (20, 30 and40 bar) and temperatures (300 and 400 ° C). The filling percent of die at various wall angles and depth to width ratios are examined. According to the dimension of channels, maximum and minimum thinning percentage at high temperature and pressure are investigated. Results show that at wall angle of ∝=0, and the depth to width ratio of h/w=0.5, rupture occurs at pressure of 20bar and at temperature of 300° C and at pressures of 20 and 40 bar at temperature of 400° C. The best channel filling with lowest thinning obtained at ∝=15 and h/w=0.5.

In this article effects of friction stir welding (FSW) tool rotational and traverse speeds were studied on heat generation and temperature distribution in welding zone of AA1100 aluminium alloy. Computational fluid dynamics method was used to simulate the process with commercial CFD Fluent 6.4 package. To enhance the accuracy of simulation in this Study, the welding line that is located workpieces interface, defined with pseudo melt behaviour around the FSW pin tool. Simulation results showed that with increase of FSW tool rotational speed, the generated heat became more and dimensions of the stir zone will be bigger. The calculation result also shows that the maximum temperature was occurred on the advancing side. The computed results showed that with increasing tool linear speeds the heat generation experienced growth down trend. With increasing traveling speeds the time to reach maximum temperature in stir zone growth but the tool rotational speed dose not effect on time to reach maximum temperature. The model outcomes shows that more than 85% total heat was produced by tool shoulder and the maximum heat with selected parameters in this study was 801 kelvin degrees.

In this article, effects of Friction stir welding tool rotational and traverse speeds were studied on the temperature distribution, material flow and formation of defects in the welding zone. Computational fluid dynamics method was used to simulate the process with commercial CFD Fluent 6.4 package. To enhance the accuracy of simulation in this Study, the welding line that is located between two workpieces, defined with pseudo melt behavior around the FSW pin tool. Simulation results showed that with increase of FSW tool rotational speed to linear speed, the material flow in front of tool became more and dimensions of the stir zone will be bigger. The calculation result also shows that the maximum temperature and stir of the material was occurred on the advancing side. The computed results showed that with incompetent heat generation, insufficient material flow caused around the pin and defects formed in weld root. The computed results were in good agreement with the experimental results of other researchers. Based on the welding parameters that used in this simulation, the maximum strain rate is predicted between -4(S-1) to +4(S-1) in the stir zone.