IRANIAN JOURNAL OF MATERIALS FORMING
Year:2024 | Volume:11 | Issue:1|Papers Count:6

In the friction stir welding (FSW) process, a special rotating tool is used for welding different parts without utilizing any electrode as filler material. By rotating the cylindrical tool and sinking it into the line of connection between two parts, friction and disturbance are created, and at the same time, heat and pressure also rise to prepare the conditions for the welding. During the last two decades, a large number of research has been carried out to investigate the mechanical properties and microstructure of joints made from several similar and dissimilar alloys. Crack growth resistance of such joints under tensile, shear and mixed loading is an important design parameter to evaluate the lifetime of welded parts in friction stir welding, while there is limited research on combined mode I/II in FSW welding. To fill this research gap, in this research tensile and fracture strength in dissimilar FSW welding of AA5083/AA5052 aluminum alloys are investigated experimentally. For this purpose, two pin diameters, three pin rotation speeds and welding speeds have been selected as welding variable parameters. After carrying out the welding, the tensile and cracked mixed mode fracture tests were performed to determine the effect of considered parameters on the tensile and fracture strength of the joint. The results showed that the biggest tensile and fracture strength happens in different tool rotation and welding speeds for different loading angles (fracture modes).

High entropy alloys are a new class of materials that have attracted much attention due to their attractive properties. High entropy alloys have various types and structures, among which, eutectic high entropy alloys have received much attention due to their unique characteristics. In this study, the effect of 60% cold rolling on the properties of AlCoCrFeNi2.1 eutectic high entropy alloy is investigated and compared with the casting condition. This alloy shows a layered structure consisting of FCC and BCC phases in both as-cast and cold-alloyed samples. In the as-cast state, the alloy showed a hardness of 352 Vickers, which increased to 401 Vickers following a 60% cold rolling. To further investigate the mechanical properties, both samples were subjected to a shear-punch test (SPT). According to the results, the as-cast sample shows good flexibility and strength which has subsequently risen following cold rolling. The measured values of the yield shear strength and final shear strength for as cast and 60% cold-rolled samples are 204, 269, 294, and 317, respectively.

This study focuses specifically on the combination of two methods: powder metallurgy and severe plastic deformation. In this research, the influence of a single pass of simple shear extrusion (SSE) on the grain refinement, structural evolution, and some tribological properties of pure aluminum samples produced through the powder metallurgy method has been investigated. It is observed that after a single pass through the channel of SSE, the average grain size decreases, and the tribological properties of the sample significantly increases. The innovation of this research lies in the simultaneous combination of two methods: Fabrication of samples through powder metallurgy and severe plastic deformation. These methods lead to the alignment or even enhancement of the properties of the produced samples compared to conventionally cast samples. The recorded hardness values for the produced samples decreased from 57 Brinell for the as-cast sample to 29, 43, and 60.3 Brinell after initial pressing, sintering, and a single pass of SSE, respectively. Wear test results also indicate a substantial improvement in wear resistance in the refined-grain sample, with a weight loss reduction of 0.011 grams compared to the powder metallurgy stage. Furthermore, corrosion test results show an increase in corrosion potential from 730 to 720 millivolts in the powder metallurgy sample after SSE, and the current density decreases from 1.71 to 1.54 amperes per square centimeter in the powder metallurgy and simple shear extrusion samples, respectively.

Despite the definition of failure being almost thoroughly studied in other theories such as elasto-plasticity, this paper studies the possibility of capturing or defining some limit states in hypoelastic materials. It is shown that for many hypoelastic materials the limit state, as a notion of failure, can take the place of the yield or failure in classical plasticity. The procedure is general, and all equations are rational, i.e. they are not dependent on a particular form of a constitutive equation. Constitutive equations cover those applied to both metallic and non-metallic materials. Some practical results were obtained for a particular form of a hypoelastic equation which resembles the Drucker-Prager criterion for the form of the limit state. Results were also examined against a set of experimental data.

Wire EDM is a modern machining process that uses electrical discharge to cut workpieces. High temperatures generated by wire EDM can cause surface cracking due to metallurgical changes. A new approach is to use the ultrasonic peening treatment to cause surface severe plastic deformation to improve the mechanical properties, especially the hardness. In this study, the focus was on exploring the impact of cutting types in wire EDM, feeding rate, and the number of peening passes as input parameters on Mo40 (1.7225) alloy steel. The experiments were designed using the multilevel factorial design method. The average hardness values were then analyzed based on the input parameters. The maximum hardness value was determined through optimization using the multilevel factorial design method. Analysis of variance was used to evaluate the impact of parameters on hardness. The highest hardness value of 952.7 (HV) was obtained with a feeding rate of 0.12 (mm/rev) and 3 peening passes in roughing mode, leading to a 48% increase in hardness. A mathematical model with 99.87% desirability was developed to study the correlation between input parameters and response variables. The hardness distribution in the peened workpieces continued up to 200 µm below the surface layers. The highest hardness was found at a feeding rate of 0.12 (mm/rev), which influences the time needed to alter dislocation density and form a new sublayer structure. Overall, increasing the feeding rate decreases hardness, while increasing peening passes increases it. According to a single-objective optimization, the cutting types, feeding rate, and number of peening passes respectively affect hardness value.

The strength of aluminum Al5083 laminated composite in accumulative roll bonding (ARB) is increased using Al2O3 nanoparticles. For this purpose, the ARB process was conducted at room temperature without lubricants in four consecutive passes. A thickness reduction of 50% in each pass was considered with no heat treatment between sequential passes. In each pass, Al2O3 nanoparticles were placed between the layers. Finally, the produced metal composite was evaluated for microstructural and mechanical properties using optical microscopy, and uniaxial tensile, microhardness, and peeling tests according to the relevant standards. The primary objective of this research was to enhance the tensile strength of the composite after work hardening by incorporating nanoparticles and annealing in the final cycle. The results showed that with an increase in accumulative roll bonding cycles, tensile strength and hardness increased, and this increase occurred more prominently in the initial cycles. Furthermore, the amount of elongation decreased at the end of the first pass and then increased until the end of the fourth pass. These changes in mechanical properties during the ARB process are due to the dominant mechanisms of work hardening and strain hardening in the initial cycles and the improvement in microstructure and refinement of grains in the final cycles of this process. The highest tensile strength and microhardness, which increased by 48.1% and 55.9%, respectively, compared to the initial sample were measured at the end of the fourth cycle. Additionally, comparing the heat-treated sample with Al2O3 nanoparticles to the base metal showed a 34.9% increase in strength and a 30.8% decrease in elongation.