a. afsari

In this study, Tube cyclic Extrusion Compression (TCEC) process was performed on copper pipes at ambient and 200°C (dynamic recrystallization activation threshold temperature) and the effect of process temperature on microstructure and mechanical properties were investigated. The results showed that by applying TCEC at ambient temperature, an equiaxed crystalline structure with an average grain size of 370 nm was obtained while by increasing the forming temperature to 200°C, the equiaxed grains with average size of 720 nm resulted. Applying the TCEC process at ambient temperature on a copper tube, increased its yield strength from 116 to 242 MPa and its average hardness from 69.2 to 101.4 Vickers while at the forming temperature of 200°C, the yield and ultimate strength were about 217 and 225 MPa, respectively, and the average hardness value was about 86.8 Vickers. Therefore, performing TCEC process at 200 °C on copper reduced the strength by 10% and increased the elongation to fracture by 21% compared to the cold forming state.

Optimization of Stir Friction Welding parameters such as linear and rotational speed of the tool can be effective to a large extent in improving welding properties. In this research, welding of two sheets of Aluminum of Al-7075 and Al-6061 were validated based on theoretical relations and numerical simulation. The simulation of the contact characteristics of the workpieces with the tool was done using the contact algorithms available in the Ansys software. From the FEM, rotational and linear speed and diameter of the tool were selected as design variables, and multi object optimization was carried out with genetic algorithm and RSM to reach the lowest tool temperature and residual stress.The parametric analysis of FSW of the threaded and non-threaded tool pins showed that the generated heat has proportional and inverse relation with rotation and linear speed of tool respectively. Tool with a diameter of 20 mm showed minimum residual stress in the workpiece. By increasing welding speed, the temperature curves become more compact and the effect of thread on heat generation was more evident in all cases at lower heat input.

In this study, the mechanical and tribological properties of 4 different types of welding filler metals were examined on a 1.6959 steel (DIN35NiCrMoV12-5) by the Gas Tungsten Arc Welding process. The fillers used in this study include ER70S-6, ER80S-G, ER80S-Ni1, ER80S-B2. The main reasons for choosing these fillers in this study are their availability and close chemical composition to the base metal. To evaluate the weld and quality of weld joints, tensile, impact, hardness and abrasion tests performed on the samples and related microstructures was investigated by optical microscope. The results indicated that the presence of molybdenum and chromium alloying elements in ER80S-B2 filler and related microstructure at HAZ has led to an increase in weld strength up to 38 percent. The best and worst wear resistance obtained from the filler ER 80S-Ni1 and ER 70S-6 respectively. The best weld quality and mechanical properties were acquired in welding using ER 80S-B2 welding filler metal.

Stainless steel cladding is the formation of an alloy by creating a thin layer of stainless steel on another metal. In this research, a layer of SA240-TP316 austenitic stainless steel was coated on SA516-GR60 steel. Experiments were conducted to compare the mechanical properties of SA240-TP316 and claded SA516-GR60 steel welds in order to investigate the possibility of replacing the SA240-TP316 steel alloy. Examining the results of the chemical analysis of SA240-TP316 alloy shows that the coating has a similar chemical composition to SA240 alloy and with increasing depth, the hardness of the weld metal and the percentage of chromium is higher and the percentage of molybdenum in the weld alloy is lower. Comparing the ultimate strength of SA516 alloy after cladding and welding with SA240 stainless base alloy shows the improvement of tensile strength. In the first case, the strength changes in the range of 470 to 503 MPa and in the second case in the range of 477 to 570 MPa. The highest hardness was obtained in the heat affected area. Bending test showed that bending without cracking up to 180 degree angle is a sign of weld metal remaining ductile. The results of the impact test also show the ability to absorb energy, especially around the voltage of 150 volts.