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The main aim of this experiment is to investigate the effects of Nano-size Al2O3 on the mechanical properties and microstructure of multi-passes friction stir welding of Al 2024 lap joint. Nano particles were added into the joint line. A combination of rotational speed and travelling speeds were performed. Optical microscopy and scanning electron microscope were used to investigate the microstructure and fracture surface of samples respectively. Optimum condition (sample) was selected due to highest ultimate tensile strength (UTS). It was seen that sample which included Nano particles and fabricated by 1400 rev/min rotational speed and 16 mm/min travelling speed in second pass of continues welding had improvement in UTS in comparison to one pass welded sample of particle free and after that increasing the number of passes reduce the UTS. The average micro hardness of the sample which was particle rich were increased in comparison to particle free sample in nugget zone. Increasing the number of passes was not effect average micro hardness in nugget zone significantly. Grain sizes were reduced by 2 passes welding and after that no significant reduction has been seen.

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To determination of equal-channel angular pressing(ECAP) process on the stress-strain behavior of  steel core of steel/copper bimetal and also effect of Cu-shell thickness on the created surface stretch during ECAP, the bimetallic samples composed of steel rods with 8 mm diameter and copper shells with 0.75 mm thickness are prepared. The both bimetallic samples and steel rods with 9.5 mm are subjected to consecutive ECAP process using die with inner angle 90^o and an outer curvature corner angle of 30^o. The applied load and punch displacement are recorded during samples passing through an ECAP die. The tensile testing is carried out on both the initial and ECAPed series. Moreover, dependence of surface stretch to diameters, shell thickness and strength properties of constituents of core/shell bimetallic rods is analytically modeled. Then, the finite element method(FEM) is used to investigate the effect of Cu-shell thickness. The obtained results revealed that the ultimate tensile strength of bimetallic core and steel rods are improved approximately 60% and 108% by ECAP deformation, respectively. The applied punch load for passing of bimetallic sample through an ECAP die is 54% less than the ones for steel rod. According to the FEM results, the maximum value of surface stretch is linearly decreased with increasing the thickness of copper shell. The obtained results show a good agreement between the analytical model and FEM approach.

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In this study, the effect of selective laser melting parameters on the mechanical properties of iron has been experimentally investigated. The mechanical properties discussed in this article are ultimate tensile strength. The selected parameters include the laser power, the laser scanning speed, and the laser hatch distance, and the design of experiments was done by the Taguchi method. By examining the microstructure, the optimal range of the mentioned process parameters was determined to achieve the highest tensile strength. The results show that the optimum parameter levels for the tensile strength include the laser power of 200 watts, the laser scanning speed of 600 millimeters per minute, and the hatch distance of 70 micrometers.