جستجوی مقالات مرتبط با کلیدواژه « heat treatment » در نشریات گروه « مکانیک »

With the emergence and expansion of additive manufacturing processes, especially the fused deposition modeling process, extensive research has been conducted on these processes. One important research area is strengthening the printed parts by the fused deposition modeling method. One of the main areas of research is related to the strengthening of printed parts by the fused deposition modeling method. This process enables the production of complex structures and the customization of parts. On the other hand, polylactic acid material is one of the main materials used in this process, which has been noticed over other materials due to its biocompatibility and biodegradability properties. In this research, the effect of annealing heat treatment on the compressive strength and modulus of porous samples has been investigated with the approach of using them in tissue engineering as a scaffold for bone tissue. The samples are 3D printed with wiggle, grid, and honeycomb patterns and with filling percentages of 40, 70, and maximum. In addition, the effect of two parameters, the extrusion width, and the layer height, has also been investigated. To create porous structures with interconnected porosities, the pattern of filling in each layer is rotated to a certain extent, and this causes the introduction of new porous structures that can have wide applications such as being used as scaffolds in tissue engineering. After evaluating the compressive mechanical properties of the samples, the same samples were heat treated, and then their compressive mechanical properties were also evaluated. The obtained results show that the maximum compressive strength and modulus occur in the sample with an extrusion width of 0.6 mm, layer height of 0.25 mm, wiggle filling pattern, and maximum filling percentage. The values ​​of compressive strength and modulus for the non-heat-treated sample are equal to 84.51 MPa and 2.28 GPa respectively and for the heat-treated sample, it is equal to 105.44 MPa and 2.29 GPa respectively.

Hardening heat treatment is one of the most important processes used in manufacturing the oil extraction machine’s cylinder. During heating operations, thermal stresses are created. This would lead to internal defects because of screw pressure and finally cause failure and decreases in machine life time. In this paper, different heating heat treatment cycles for an oil extraction machine’s cylinder made of stainless steel AISI420 were investigated by experimental and numerical methods. Since the residual stress is the main factor that affects the failure in the cylinder, the cycle with minimum stress is chosen as an optimum condition. The accuracy of the results of the simulation process is evaluated by providing experimental samples. Also, different heat treatment cycles were designed by the TAGUCHI method. Then, tensile test specimens were prepared from experimental samples, and their mechanical properties were compared. Finally, preheating at 790 °C for 30 minutes, the second stage preheating at 900 °C for 30 minutes, the Austenitic process at 1056 °C for 30 minutes, Quenching in oil at 80 °C for 10 minutes, the first stage tempering process at 370 °C for 90 minutes and the second stage tempering process at 370 °C for 90 minutes was considered as the best condition for hardening heat treatment cycles.

7075 aluminum alloy, with a high strength-to-weight ratio and good impact strength, is one of the useful materials in the aerospace and automotive industries. However, this alloy has limitations such as poor formability, high spring back at low temperatures, and thermal distortion during hot forming. To overcome these limitations, a thermomechanical process including solution heat treatment, forming, and quenching in the die can be used. In this research, for producing a U-shape part with a depth of 30 mm, a 7075 sheet with a thickness of 2 mm was first subjected to solution heat treatment at a temperature of 480 ℃, and then was immediately transferred to a cooling die to be formed at a temperature of 4 ℃ under a hold time of 20 seconds. Finally, the part was artificially aged to improve its mechanical properties. A finite element simulation of the process using the ABAQUS software was also performed. Good dimensional accuracy and absence of rupture in the final U part, close agreement between the experimental and simulation results, an acceptable 25% reduction in elongation, very close tensile strength to the base material, and microhardness equal to 95% of the base material are the results of this research.

Grinding, as one of the machining processes, is considered as one of the most important final production processes. During this process, very high heat is generated, which is a problem in the machining process, and efforts are made to remove it. Recently, efforts have been made to use this problem as an opportunity. By controlling the amount of heat transferred to the workpiece, its surface can be heat treated. Therefore, grind hardening is a new and non-traditional machining process that can be used for surface hardening and grinding of metal parts. Grind hardening process has the potential to replace the traditional methods of surface heat treatment by integrating this process in the grinding phase. The key advantage of this method is the elimination of workpiece movement during production, reduce cost, increase efficiency, and the reduction of redundant setups. In this research, the functional principles of the process, the latest developments of this method and a comparison between this process and alternative methods of surface heat treatment have been discussed. Its challenges have been discussed and examined, and the opportunities and situations of using grind hardening by have been stated.

Thin-walled tube bending is one of the important processes for manufacturing parts in the automotive and aerospace industries. This paper investigates the effect of heat treatment on the bendability of thin-walled tubes made of AA6063 alloy. With the hydro rotary draw bending process, the cross-section ovality of the as-received, annealed, and artificial aged tubes has been examined at different fluid pressures. In the experiments, the tube diameter to tube thickness ratio was 13.88. Also, the critical bending ratio was 1.6, and the bending angle was 90 degrees. By examining the results, it has been found that heat treatment and fluid pressure had an important effect on the quality of the bent tubes. By increasing the fluid pressure to 3.6 MPa, critical cross-section ovality has decreased in all specimens. The maximum decrease of cross-section ovality is obtained in the annealed sample by 49%. Also, in the artificially aged specimens, the critical cross-section ovality decreases by about 45%. It has also been observed that at a pressure of 3.6 MPa, the critical cross-section ovality of the annealed sample has improved by 19% compared to the artificially aged specimens.

In this article, the effect of the work piece geometry and microstructure grain size on the heat treatment of 1050 steel has been investigated. For this purpose, two samples of work pieces with round (cylindrical) and square (flat) sections were considered for simulation with AC3 software. The effect of each of them was investigated on the growth of grain size in different cooling environments. Also, the hardness at the surface and depth was evaluated for both conditions. The results of the simulation show that the used software has a suitable ability to predict surface and depth hardness, grain size and the behavior of CCT parameters and cooling curves in the heat treatment of 1050 steel and this method can be used on a workshop scale and to be used in industrial applications.

In internal combustion engines, due to cyclic loading and wear between the upper surface of the piston ring and the upper groove of the piston, the fretting fatigue phenomenon could occur. In this research, the effect of lubrication and the heat treatment on the fretting fatigue behavior of aluminum-matrix nano-composite have been investigated. The fretting fatigue test was performed in fully-reversed loading condition and at the room temperature. In addition, the S-N curve and fretting fatigue properties of piston alloys were obtained. The microstructure and the fracture surface were examined by the optical and microscopy and the field emission scanning electron microscopy. The results showed that the failure behavior was brittle. In addition, the lubrication and the heat treatment improved the fretting fatigue lifetime of the piston alloy.

In this research, Inconel 738LC as the base metal was joined by wide gap brazing (WGB) using the mixture of Amdry718 as high temperature particle (HTP) and BNi-2 as low temperature particle (LTP). By using Amdry 718, the brazing temperature can be increased and porosity reduced significantly due to higher melting point temperature than base metal. The effect of mixture ratio on the microstructure and the mechanical properties was studied. The amount of the LPT in the mixture was 30, 40, and 50 percent. By decreasing the LTP ratio, the amount of eutectic phase and the blocky boride in the solid diffusion zone (SDZ) decreased markedly. The joint width increased by increasing the amount of LTP. There were two distinct regions in the joint/base interface. Due to the diffusion of B into the base, adjacent to the joint, the grain boundary melted and created a region including both the isothermal solidification zone (ISZ) and SDZ. By getting away from the joint, the content of B reduced by the grain-boundary diffusion. It was observed that aging did not have a significant effect on the amount and distribution of eutectic phases and blocky borides, however, the morphology of these phases changed slightly. Moreover, aging had a small effect on hardness making the hardness of different phases more uniform.

In the present study, Cu/Zn/Al multi-layered composite was processed by accumulative roll bonding (ARB) through nine passes. Afterwards, heat treatment processes at various temperatures (750-950℃) and times (10-25min) were done on the prepared composites to fabricate CuZnAl shape memory alloys. The microstructure (composites and alloy) were investigated using scanning electron microscopy and X-ray diffraction. Tensile properties and shape memory effect of the composites and alloys were also investigated by tensile test. The microstructure investigations show that plastic instability and shear bands occurred in different layers in the composite. In addition, a composite with a uniform distribution of Zn and Al reinforcing layers was produced after nine passes. The tensile strength of the composite increased from the first cycle to the third ARB cycle and then decreased from the fifth to the ninth ARB cycle. Finally, the best UTS (about 330MPa) and elongation (about 31.52%) values were obtained on the third and first pass, respectively. The results showed that CuZnAl shape memory alloy was successfully fabricated by the accumulative roll bonding process and next heat treatment. It was also found that the alloys treated at 900°C and cooled in ice water consist of martensitic phase. Additionally, the alloy annealed at 900°C for 15 minutes exhibited a good shape memory effect and strength (about 503MPa).

Aluminum-silicon alloys have vast applications in-vehicle components, such as the piston. Usually, such parts are under thermal and mechanical cyclic loadings, and therefore, they should have enough fatigue strength. For strengthening methods, the heat treatment and the addition of nanoparticles could be mentioned. In this research, the effect of the simultaneous use from SiO2 nanoparticles and the heat treatment was investigated on the high-cycle fatigue lifetime of the piston alloy, which is the novelty of this study. The stir-casting method was used for adding nanoparticles into the aluminum matrix, and the T6 heat treatment was done on samples. The microstructure was examined by the optical microscopy and also the field-emission scanning electron microscopy (FESEM), and high-cycle bending fatigue tests were performed, under fully-reversed loading conditions. Based on FESEM images, no agglomeration of nanoparticles was observed in the matrix. In addition, it was found that using SiO2 nanoparticles, heat treatment, and the combination of two approaches, caused to the improvement of the fatigue lifetime, for 304, 411 and 237%, respectively. According to high-cycle bending fatigue data, the fatigue strength coefficient of the piston alloy increased by the heat treatment, and the addition of nanoparticles.

In this study, corrosion and mechanical properties of AISI 420 martensitic stainless steel after welding and heat treatment were studied. Heat treatment cycle in order to optimize the mechanical and corrosion properties of the steel after welding was investigated. After TIG welding and heat treatment of tempering, hardness and tensile, and impact mechanical tests and corrosion polarization tests were performed on the samples. Also to study the microstructure and identify the type of the happened corrosion, by optical microscopy and transmission electron microscopy (SEM), the samples were examined. By The results of mechanical tests and corrosion, heat treatment conditions to achieve optimum mechanical properties and good corrosion properties was determined after welding. In conclusion, the cycle of heat treatment of tempering at a temperature of 300˚C and 1 hour, is an appropriate cycle in order to achieve Suitable corrosion and mechanical properties for welded 420 stainless steel.

In the present article, T4 and T6 heat treatments carried out to improve microstructure and mechanical properties (hardness and tensile) of Al-Si-Cu alloys (A380 alloy, which has been used in engine cylinder heads). For this purpose, solution annealing was performed at 490 ºC for 5 h. The T6 aging was executed at 180, 200, 220, 240 ºC for 1, 3, 5, 7 h. Hardness experimental results showed that optimum values for the T6 aging temperature and time are generally 200˚C and 3 h, respectively, as the hardness increased. Evaluation of the microstructures and fractured surfaces were performed with optical and scanning electron microscopes. After T6 treatment, tensile strength increased from 245 to 255 MPa and hardness from 88 to 95 Vickers. By applying T6 process in optimized tempeIn current paper two different regimes of heat treatments, namely T4 and T6 treatments of Al-Si-Cu alloy used in engine cylinder head were investigated and the effects and significance of time and temperature on microstructure and mechanical properties of the material were studied and compared. For this purpose, solution annealing was performed at 490 ºC for 5 h. The T6 aging was executed at 180, 200, 220, 240 ºC for 1, 3, 5, 7 h. Hardness testing results revealed that the optimum hardness is obtained for T6 at 200˚C and 3h, respectively, as the hardness increased. Evaluation of the microstructures and fractured surfaces were performed with optical and scanning electron microscopes. After T6 treatment, tensile strength increased from 245 to 255 MPa and hardness from 88 to 95 Vickers. By applying T6 process in optimized temperature and time, the hardness and tensile strengths of Al-Si-Cu alloy was enhanced from 10.5% compared to that of the T4 processes. The sensitivity analysis indicated that effect of the aging temperature is more significant in comparison to other parameters.
rature and time, the hardness and tensile strengths of Al-Si-Cu alloy was enhanced from 10.5% compared to that of the T4 processes. The sensitivity analysis indicated that effects of the aging temperature are more significant in comparison to other parameters

In this paper, the effect of heat treatment on the impact behavior of A356 aluminum alloy foams reinforced by SiC particles was studied and new results was generated. The foam was manufactured by direct foaming of melts with blowing agent CaCO3. A number of foam specimens were processed by T6 aging treatment. The drop-weight impact test with a hemispherical striker tip and velocity of 6.70 m/s was carried out on five untreated foam specimens and five heat-treated foam specimens, and the load versus time history data was obtained. The obtained impact response of A356/SiCp composite foam includes three stages: an elastic region, a plateau of load region and complete failure region. In plateau region, the plastic deformations can be tolerated by the foam at nearly constant load. The small amounts of standard deviation and coefficient of variation (for different parameters) obtained from statistical analysis of experimental data indicates the reliance on the results for quantitative analysis of them. The measurements showed that heat treating of Al foam results in an increase of the plateau load level and energy absorption capacity of the foam with 48.1% and 40.3% increase respectively. The length of plateau region is also decreased due to heat treatment. Regarding the significant improvement of mechanical properties of the foam and increase of its impact strength, the heat treatment after foam casting can be considered as a suitable approach for various industrial applications of aluminum foam.

Nowadays, one of important parts in combustion engines is the turbo-charger, which could improve the performance. Such this component and especially blades of the turbine, is working at high temperatures. Based on this condition and according to centrifugal forces in blades, one of design parameters is the creep strength of the material. For such condition, nickel-base super-alloy has been utilized. In this article, the hardness of 713C nickel-base super-alloy (which has been used in turbine blades of engines) increased by a typical heat treatment. For this objective, the design of experiments was utilized and the hardness through parallel and vertical lines to the grains direction in the material micro-structure was measured at different values of the solution temperature and time in the heat treatment. Experimental results showed that optimum values for the solution temperature and time are generally 1200˚C and 60 min, respectively, when the hardness increased. The sensitivity analysis indicated that effects of the temperature parameter are more significant in comparison to other parameters.

Cold spin bonding is a new invented method for producing layered composite tubes based on flow-forming process. Bonding strength in this process is dependent to parameters such as initial thickness, rate of deformation, bonding temperature, initial strength, heat treatment temperature, duration of heat treatment and also production parameters like feed rate and spindle RPM. In the present work, effect of rate on thickness reduction, heat treatment temperature and duration of heat treatment on bonding strength of steel and aluminum have been studied. The strength of bonding which produced by cold spin bonding has been measured by peel test and structure investigation has been done by scanning electron microscopy. Among the parameters, heat treatment temperature and after that thickness reduction rate have the most effects on bonding strength and heat treatment duration has less effect in comparison. The results show that the increase of heat treatment temperature up to a certain level increase bonding strength, but above that level the strength will decrease.. This study also has shown that the best condition occur in %50 thickness reduction, heat treatment temperature of 475 degree and 120 minutes of heat treatment in which bonding strength reaches to yield strength of base metal.

Presence of porosity and gas layers around the Al2O3 particles are one of the most important reasons of decreasing in mechanical properties of aluminum metal matrix composites. In this research, for decreasing of porosity, increasing of wettability and uniformly distribution of particles in matrix three method were used; using inert gas for injection powder with 5 liter/ min flow rate, particles heat treatment in 1100 ̊C for 20 min and mill Al2O3 particles with Al particles in ratio of Al / Al2O3= 1. The effect of these parameters on microstructure and mechanical properties of composite were investigated. The results showed that amount of porosity and agglomeration of particles were high in metal matrix composite with handy injection of particles. While injection with inert gas, using heat treatment and Al / Al2O3 milled Cause improve wettability and uniformly distribution of particles in molten Al. the results showed the maximum value of hardness, compression strength and impact energy have obtained in metal matrix composite reinforced with Al / Al2O3 milled with value of 78.7 BHN, 539.1 MPa and 8.2 Joule, respectively.

Explosive welding is used for excellent bonding of similar and dissimilar materials with the wide variety of thicknesses,area dimensions and different thermal and mechanical properties. In this study, an Al/St/Al multilayer sheet was fabricated by explosive welding process and the effects of annealing temperature on the interfacial properties of explosively bonded Al/Cu bimetal have been investigated. For this purpose, hardness changes along the thickness of the samples have been measured, and the thickness and type of intermetallic compounds formed at the joining interface have been explored by means of optical microscopy (OM), scanning electron microscopy (SEM) and also energy dispersive spectroscopy (EDS). By heat treatment of the samples at 300, 350 and 400°C, it was observed that intermetallic layer was formed at the interfaces. The obtained results indicate that, with the increase of the annealing temperature, the thickness of intermetallic compounds has increased and the amount of hardness along the thickness of the joining interface has diminished. In the annealed sample at 300 °C for 60 min, it was observed that intermetallic layers have formed at the interface of Al/St bimetals. These layers consist of the intermetallic compound Al2Fe and its thickness gets to about 35 μm at some points.