In order to evaluate the possibility of the similar and DISSIMILAR WELDING of 5019 and 7039 aluminum alloys, plates of 3 mm thick from this alloy were welded via Self-Reacting Friction Stir WELDING (SRFSW) method. Floating bobbin tool was designed and manufactured from heat –treatable hot working steel to perform the WELDING process. The effect of various process variables such as the shoulders pinching gap, the tool transverse speed and the tool rotational speed were investigated to establish a defect-free joint. Following the visual inspection and X-ray radiography, it was found that a defect-free joint is obtained at the transverse speed of 22 mm/min and rotational speed of 1120 rpm. The results of tensile test, also, revealed that the joint efficiency of 5019-5019, 7039-7039 and 7039-5019 joints are 72, 76 and 91. 5%, respectively. Accordingly, these amounts were more than the joint efficiency of the fusion WELDING, and comparable with/more than the joint efficiency of Conventional Friction Stir WELDING (CFSW). Microscopic evaluation of the fracture surface of welded pieces indicated that the dominant fracture mechanism for similar joints is the soft fracture, while the one for non-similar fracture is the brittle fracture. Assessment of the cross-sectional hardness of the welded pieces near the upper and lower shoulders showed that the degree of hardness near the lower shoulder of the tool is always higher, which can be attributed to the lower temperature of the work piece in this area.

Lap joints of commercially pure magnesium plates to aluminium plates (Magnesium plate on the top, and Aluminium plate, grade 1100, on the bottom side) were conducted by friction stir WELDING using various traveling and rotation speeds of the tool to investigate the effects of the WELDING parameters on the joint characteristics and strength. Defect-free lap joints were obtained in the WELDING traveling speed range of 40-80 mm/min, and rotational speed range of 1200-1600 rpm. The shear tensile strength of Mg/Al joints increased as a result of decreasing the WELDING speed from 120 to 40 mm/min at constant rotation speed of 1600 rpm. Defects such as surface grooves, excessive flash, tunnels, and voids were observed if the joints prepared out of the mentioned range. The effects of the WELDING parameters are discussed metallographically based on observations with optical and scanning electron microscopes.

In this paper, finite element modeling of friction WELDING of two ASTM A106-B and AISI 4140 DISSIMILAR pipes is investigated. The effect of the friction WELDING parameters including rotation speed, friction pressure, friction time, forging pressure and forging time on the axial shortening are investigated using a fractional factorial design method. Because of the extreme material deformation, an innovative remeshing technique was scripted in Abaqus CAE to prevent the creation of distorted elements.27 models were solved and 3 validation experimental tests were carried out. Results showed that increasing the all parameters cause larger axial shortening. Friction pressure with 33.9% had the most effect on the axial shortening. Moreover, an increase in forging pressure and forging time has a limited effect on the axial shortening. After about 2 seconds from the beginning of the WELDING, the temperature of the interface becomes steady at about 1250oC. The validation tests revealed that the simulation error was about 5.6% which shows a good agreement between the finite element results and the experimental data.

Overlapped strips of titanium grade 2 and aluminum 3105-O alloy were welded together under an innovative spot-like pulse laser procedure. The tactile seam tracking on ring paths yielded reliable weld  t-up of 1 and 0. 5 mm thickness strips. Since the WELDING parameters of Ti-Al were narrow, three WELDING speeds of 4, 5, and 6. 67 mm. s-1 were chosen for the pretest conditions. The microstructural investigations showed that intermetallic compound Ti3Al formed in the Ti-rich fusion zone. Cracks formed in the Al-rich fusion zone as a result of TiAl3 precipitation. Dimple fracture occurred at 6. 67 mm. s-1 WELDING speed. Longer mixing time at Ti-Al interface occurred at lower WELDING speeds of 4 and 5 mm. s-1, which led to the formation of thicker intermetallic compounds and more massive crack generation. It also increased the hardness of the fusion zone and resulted in brittle fracture type during the tensile test. The highest strength was achieved with a WELDING speed of 4 mm. s-1, which was a result of more massive weld nugget and lower porosity.

Ultrasonic WELDING is gaining popularity for joining of thin and DISSIMILAR materials and foils in the fabrication of automotive Li-ion battery packs because of excellent efficiency, high production rate, high WELDING quality, etc. Precise control of the parameters of the WELDING process plays an important role in achieving good joint quality. Numerical simulation can greatly help control the main input parameters such as frequency, clamping pressure, friction coefficient, and vibration amplitude. In this present work, a three-dimensional thermo-mechanical Finite Element (FE) model is proposed using ABAQUS/EXPLICIT for the DISSIMILAR Al to Cu weld to predict the deformation and temperature as output parameters during WELDING process by varying input parameters. The simulation results showed that the clamping pressure, vibration frequency and friction coefficient have a great influence on heat production during the process which was critical to determine the final quality of the welded joint. Studies also showed that increased clamping force and WELDING frequency led to increased deformation.

In this paper, thermo-mechanical behavior of the WELDING process was analyzed to determine the effect of edge preparation on the residual stress magnitude and distribution in DISSIMILAR joints. By using a verified finite element model, an efficient user subroutine was developed to consider the effects of phase transformation. In order to verify the model, experimental data for similar and DISSIMILAR joints, obtained by deep hole drilling method, were utilized. Good agreement was observed between the finite element and experimental data. The results indicated that the developed computational method is an effective tool to predict the residual stress of DISSIMILAR weld joints. The present finite element model was developed in a butt-welded pipe to consider the effect of pipe wall-thickness, groove shape and root opening distance. It was observed that the pipe wall-thickness has important influences on the distribution and magnitude of residual stress. Moreover, By increasing the pipe thickness in the DISSIMILAR butt-welded pipes, tensile axial residual stresses on the inner surface of the DISSIMILAR joint decreased on the stainless steel side, but only a small variation was observed on the carbon steel side.The compressive axial residual stresses on the inner surface and the tensile axial residual stresses on the outer surface increased by increasing the pipe wall thickness, especially on the carbon steel side.Increasing the weld groove shape and root opening distance leads to higher compressive axial stresses on the inner surface and higher tensile axial stresses on the outer surface, only on the carbon steel side.

Increasing usage of magnesium and aluminum light metals in the transportation industry has made joining of these two metals one of the challenges for researchers and engineers. The aim of this study was to investigate the relationship between mechanical properties of lap friction stir welded Al-Mg plates and characteristics of the interface. Therefore, joining of aluminum and magnesium in various conditions was conducted. Optical and scanning electron microscopy analysis, micro-hardness test and tensile tests were performed on samples. The results showed that in the joints where Mg was on top, an approximately 10 micron thick layer of intermetallic compounds is created, while in the Al-top joints, approximately 1 mm thick intermetallic compounds with solidified microstructure were visible.Mechanical test showed Mg-top joint has higher strength in comparison with Al-top joint. On the other hand, hardness test of Mg-top joint showed more fluctuation than Al-top joint. Microstructural investigation also showed that in the Mg-top joint, formation mechanism of intermetallic compounds has occurred in solid state while in the Al-top joint, in addition to diffusion in solid state, eutectic formation in the molten state and solidification has occurred.

The relatively new solid state WELDING process friction stir WELDING (FSW) was applied in this research work to join similar and DISSIMILAR aluminum alloys AA5754-H22 and AA6063-T4. Different WELDING rotational speed and transverse speed applied. The joint which was fabricated using tool rotational speed of 2000 rpm and transverse speed of 4 mm/min yielded the best mechanical properties. Soundness of joint was proved by non-destructive tests such as visual inspection and radiography. The global mechanical behavior of the similar welds is very similar to that of the base material. For DISSIMILAR weld important losses in ductility was reported. Microstructural evaluation of fractured surface showed that ductile fracture was the major fracture mechanism of similar and DISSIMILAR welds.

In this research, DISSIMILAR WELDING of NiTi shape memory alloy to AISI 304 austenitic stainless steel Archwires was investigated. For this purpose, common straight orthodontic archwire with rectangular cross-section and dimensions of (0. 635 × 0. 432 mm) were selected and the laser WELDING technique was used to connect the wires. The microstructure, chemical composition and phasesin the weld zone of the joints werestudied with Optical microscopy (OM), Scanning electron microscopy (SEM) equipped with EDS analysis system, focused X-ray diffraction (Micro-XRD). Also, the mechanical properties of the weld zone were investigated by using Vickers microhardness test. Microstructure investigation showed that the obtained microstructure from the laser weld of these alloys has a dendritic and nonhomogeneous structure. According to XRD analysis, brittle intermetallic compounds such as Fe2Ti, Cr2Ti, TiNi3, and Ti2Ni wereformed during laser WELDING in the weld zone. Formation of these brittle intermetallics caused increasing the hardness of the weld zoneabout 800 HV. and decreasing the mechanical properties. Also, Fe2Ti intermetallic particles mainly formed in the weld region near the NiTi fusion zone which results in stress concentration, micro-cracks formation and dropping joints mechanical properties. Therefore, a suitable modification process is required to control the chemical composition of the weld zone and improving the joint properties of DISSIMILAR laser welded archwires of these alloys.

Researchers have worked on many facets of joining of similar/DISSIMILAR aluminum alloys using different joining techniques and came up with their own recommendations. Friction Stir WELDING (FSW) is widely preferred for joining aluminum alloys being an economical alternative to produce high-quality welds. However, obtaining high strength welded joints without the detrimental and visible effects still needs attention considering the effect of hybrid FSW techniques, tool material and geometry, process parameters (tool rotation, WELDING speed, and plunge depth), and post WELDING treatments. This study presents the state of the art with the authors’ own inferences on the evaluation of FSW performances in terms of joint tensile strength, fatigue strength, corrosion resistance, residual stresses, microstructure, and microhardness. This study also presents attempts made by the researchers on modeling and parametric optimization of FSW to finding scope for application of advanced optimization techniques and development of predictive models for mechanical properties of welded joints. This study emphasizes more studies required on the comparative evaluation of FSW performance with the application of ultrasonic frequency combinedly or individually on advancing and retreating sides of plates.