Mechanical Properties Of Welded Specimens Research Articles

Friction stir welding of dissimilar alloy combinations—A Review

Friction stir welding (FSW) is one among solid-state welding processes that can be employed for producing joints between dissimilar combinations with more ease than that of fusion welding processes. Several high coupled physical phenomena have addressed FSW as an extremely complex process. It is around three decades of invention, optimization of the parameters have been carried out even today by many researchers all over the world to obtain sound joints. This article focuses mainly on the research developments in the dissimilar FSW (DFSW), with the factors that are involved in joint fabrication between dissimilar materials. From the literature, it is found that the most influential factors in deciding the quality of the joints are pin profile, shoulder shape, welding speed and tool rotational speed. In addition, all other parameters will provide incremental support to it. The study on microstructure in different zones and the mechanical properties of welded specimens are elaborated from the available literature. Special attention is given to the reinforcement of micro- and nano- sized solid particles in the DFSW process. Future studies of DFSW are discussed based on the untracked studies that are not available in the literature.

Investigation of Mechanical and Microstructural Properties of Welded Specimens of AA6061-T6 Alloy with Friction Stir Welding and Parallel-Friction Stir Welding Methods.

The present study investigates the effect of two parameters of process type and tool offset on tensile, microhardness, and microstructure properties of AA6061-T6 aluminum alloy joints. Three methods of Friction Stir Welding (FSW), Advancing Parallel-Friction Stir Welding (AP-FSW), and Retreating Parallel-Friction Stir Welding (RP-FSW) were used. In addition, four modes of 0.5, 1, 1.5, and 2 mm of tool offset were used in two welding passes in AP-FSW and RP-FSW processes. Based on the results, it was found that the mechanical properties of welded specimens with AP-FSW and RP-FSW techniques experience significant increments compared to FSW specimens. The best mechanical and microstructural properties were observed in the samples welded by RP-FSW, AP-FSW, and FSW methods, respectively. Welded specimens with the RP-FSW technique had better mechanical properties than other specimens due to the concentration of material flow in the weld nugget and proper microstructure refinement. In both AP-FSW and RP-FSW processes, by increasing the tool offset to 1.5 mm, joint efficiency increased significantly. The highest weld strength was found for welded specimens by RP-FSW and AP-FSW processes with a 1.5 mm tool offset. The peak sample of the RP-FSW process (1.5 mm offset) had the closest mechanical properties to the base metal, in which the Yield Stress (YS), ultimate tensile strength (UTS), and elongation percentage (E%) were 76.4%, 86.5%, and 70% of base metal, respectively. In the welding area, RP-FSW specimens had smaller average grain size and higher hardness values than AP-FSW specimens.

Microstructure and mechanical properties of laser high-velocity impact welded Ta/Cu joints

In this study, a laser high-velocity impact welding of Ta/Cu metal foil was successfully realized under different laser energies and flight distances. The morphology, microstructure, and mechanical properties of welded specimens were investigated via systematic experiments. Results indicated that the plastic deformation of the welded specimens was further pronounced with the increase in laser energy or flight distance. The welding area was ring-shaped, and the variation laws of the effective welding area under different laser energies and flight distances were summarized. The transition of the interface waveform was different when changing the laser energy and flight distance. Energy dispersive spectroscopy results showed that a trace element diffusion formed at the welding interface and intermetallic compounds were absent. Nanoindentation hardness tests showed that the hardness value increased with the decrease in distance from the welding interface. Two main failure modes of the Ta/Cu welding specimens occurred in the tensile shear tests, and the trend of the maximum tensile force under different process parameters was concluded.

Effect of the Deformation during Pressure Welding of a Wrought EP975 Nickel Alloy and a Single-Crystal Intermetallic VKNA-25 Alloy on the Structure and Properties of the Welded Joints

This work is a continuation of the studies of the possibility of formation of a one-piece blisk unit for gas turbine engines by solid-phase pressure welding (PW) of a single-crystal [001] Ni3Al-based VKNA-type blade alloy with a wrought EP975 disk nickel superalloy. The influence of the PW temperature at a strain of 10 and 24% on the structure and mechanical properties of welded specimens at room temperature is investigated. An increase in the process temperature by 50°C to 1175°C is shown not to change the structure of the VKNA-25 alloy, and the γ-phase grain sizes in the EP975 alloy increase from 7–8 to 15–18 μm. During tensile tests, the welded specimens fail through the VKNA-25 alloy, and the strength of the welded specimens fabricated at 1175°C is almost twice as high as that of the specimens fabricated by PW at 1125°C at the same strain of the EP975 alloy. Electron backscatter diffraction (EBSD) analysis of the solid-phase bonding zone demonstrates that the VKNA-25 alloy retains its single-crystal structure.

Effect of Pin Profile and Process Parameters on the Properties of Friction Stir Welded Al-Mg Alloy

In Friction stir welding (FSW), weld quality is predominantly affected by welding process parameters. The welding parameters such as tool shoulder diameter, tool rotational speed, welding speed and axial force play a major role in deciding the joint strength. In present work, FSW have been carried out on the 6 mm thick Aluminum alloy plate. Friction stir welding parameters such as the tool rotational speed and the welding speed were investigated together with the different pin profiles; the results show that the straight square pin profile leads to better mechanical properties of welded specimens. The pin profiles used in this work were the straight square (SS), straight cylindrical (SC), and taper cylindrical (TC). It was found that the straight square pin profile improves the material flow behavior and the uniform distribution of plastic deformation and reduces the formation of macroscopic defects on the welded zone. Also, it was observed that the pin profile exhibits more influence on tensile strength followed by tool rotation speed and traverse speed

Influence of axial magnetic field on shape and microstructure of stainless steel laser welding joint

The morphology and microstructure of the weld joint have significant influence on mechanical properties of welded specimens. In this paper, the mechanism on how the external magnetic field affected weld profile and microstructure was discussed by applying the longitudinal steady magnetic field to laser welding for SUS301 stainless steel. The optimal and scanning electron microscopes were used to measure the shape of the cross section and observe the microstructure after welding. The results showed that the shape of the cross section and microstructure could be significantly changed using the external magnetic field. Moreover, joint shape changed distinctly with the magnetic field intensity changing. With the increasing of magnetic flux density, the weld profile of the full penetration model changed from funnel to X type; meanwhile, the bottom weld width increased by 40%. In addition, the partial fusion zone occurred, and the weld width decreased by 20% while penetration increased by 18% when magnetic flux density turned into 380 mT. As far as microstructure of weld joint was concerned, it appeared that application of axial magnetic field led to indistinct fusion line and blocky austenite in big size rather than columnar grain in the center of the cross section. This phenomenon could be explained by numerical simulation results.

Friction stir vibration welding process: modified version of friction stir welding process

In the current research, a new method is applied to modify the conventional friction stir welding (FSW) process. Fixture, which fixes the workpieces, is shaken mechanically during FSW in a direction normal to weld line in order to increase the straining of weld region material. In other words, vibration of workpieces is accompanied by the rotating motion of tool. This new process can be described as friction stir vibration welding (FSVW). Al 5052 alloy specimens are welded by two welding methods, FSW and FSVW. Microstructure and mechanical properties of welded specimens are compared. Metallography analyses indicate that grain size decreases and hardness increases as FSVW method is applied. Tensile test results also show that strength and ductility values of friction stir vibration (FSV)-welded specimens are greater than those relating to friction stir (FS)-welded specimens. It is because of more work hardening of plasticized material, during FSVW, which leads to more generation and movement of dislocations. Correspondingly, grain size decreases and mechanical properties improve. Additionally, it is observed that the mechanical properties of the weld improve as vibration frequency increases.

Performance analysis of a pneumatic to servo converted system for electrode actuation in resistance spot welding using 304L austenitic stainless steel

A high current, AC waveform controller with C-type body frame of spot welder (75 kVA), was examined for the electrode actuating system whose pneumatically driven system has been redesigned and refitted for the servo based system without any vertical spring assistance in the 50 mm movable distance. Moreover, the pressing mechanism was carefully handled during the entire pressing tasks as to ensure that no catastrophic reaction happens for the electrodes’ caps, electrodes’ holders as well as the other part of mechanical assembly. With the mechanically originated-pneumatic and also the converted-servo systems, the stainless steels are welded for both systems to characterize the improvements. While the welding processes were carried out, the electrical signals have been captured to compute the signals’ representation of entire sequences. Later, the welded samples were underwent the tensile shear test, metallurgical observation and hardness test. The analytical results show distinct changes in the force profiles which has led to profound changes in mechanical properties of welded specimens.

Effect of Modified Pin Profile and Process Parameters on the Friction Stir Welding of Aluminum Alloy 6061-T6

This work deals with the effect of a new “bolt-head” pin profile on the friction stir welding performance of the aluminum alloy 6061-T6, compared to traditional pin profiles. Friction stir welding parameters such as the tool rotation speed and the welding speed were investigated together with the different pin profiles; the results show that the new “bolt-head” pin profile leads to better mechanical properties of welded specimens. The pin profiles used in this work were the straight square (SS), straight hexagon (SH), taper cylindrical (TC), and the straight hexagon “bolt-head” (SHBH). It was found that the last pin profile improves the material flow behavior and the uniform distribution of plastic deformation and reduces the formation of macroscopic defects on the welded zone. Mechanical tensile tests on welded specimens were performed to determine the tensile strength: the specimens welded with the SHBH pin profile have shown the highest mechanical properties. An approach is presented for material flow on this aluminum alloy using the SHBH pin profile, which is related to the improvement on the resulting mechanical properties.

Mechanical Properties of Dissimilar and Similar Cold Metal Transfer Welded Galvanized Steel 1314 and Aluminum AA1050*

Abstract This study aims to investigate the weldability of 1050 aluminum alloy (AA1050) and galvanized 1314 steel by the cold metal transfer (CMT) procedur, comparing it with respective welding of similar aluminum sheets. Mechanical properties of welded specimens were determined by tensile testing and hardness measurements. The study was completed by microstructural analysis. The results showed that CMT welding can be applied successfully to join aluminum and steel.

Friction stir spot welding of dissimilar polymethyl methacrylate and acrylonitrile butadiene styrene sheets

Friction stir spot welding (FSSW) is a new welding method which has recently been applied to polymeric materials. In this paper the feasibility of FSSW for two dissimilar polymers; polymethyl methacrylate (PMMA) and acrylonitrile butadiene styrene (ABS) is investigated. For this purpose, an improved tool equipped with an additional plate is used to make lap joint welded specimens. This study also investigates the effect of FSSW parameters on mechanical properties of welded specimens. Experimental tests were conducted according to a 33 full factorial design of experiment in which tool rotational speed, tool plunge rate and dwell time were determined as the process parameters. Signal-to-noise ratio and analysis of variance are utilized to obtain the influence of process parameters on weld strength as a mechanical property. The study demonstrates that welding of PMMA to ABS by friction stir spot welding is feasible and process parameters have a significant effect on weld strength. Three fracture modes were observed in lap-shear tests during research for this study.

A Comparison of Weld Properties with or without Filler Wire on Laser Welding of Magnesium Alloy for Car Industry

Magnesium alloys are becoming important material for light weight car body, due to their low specific density but high specific strength. However they have a poor weldability, caused by high oxidization tendency and low vapour temperature. In this study, the welding performance of magnesium alloy was investigated for automobile application. The material was rolled magnesium alloy sheet contains 3wt%Al, 1wt%Zn and Mg balance. The effects of filler wire addition was investigated on 2kW Nd:YAG laser welding. For the results, the mechanical properties of welded specimen were similar with base metal in laser welding with and without filler wire. The bridging ability was improved with filler wire without weld properties deterioration on laser welding of magnesium alloy.

Linear Friction Welding of IN-718 Process Optimization and Microstructure Evolution

Linear Friction Welding (LFW) of IN-718 Superalloy was investigated under several processing conditions. The influence of process parameters such as frequency (60Hz to 100Hz), amplitude (2mm to 3mm) and frictional pressure (50MPa to 110MPa) on the microstructure and mechanical properties of welded specimens was determined. Optical and scanning electron microscopy, and micro-hardness testing were used to characterize the welded areas as well as the Thermo-Mechanically Affected Zones (TMAZ). In-situ thermocouple measurements were performed to follow temperature evolution in the specimens during the different phases of the LFW process. The analysis of the results indicated that for some specific conditions (f=80Hz, a=2mm and P=70MPa) a maximum temperature of 1200°C was attained during the last stage of the welding process, the burn-off phase. This temperature, very close to the alloy melting range, would be sufficient to cause partial liquation in this zone. Microscopic examinations revealed the presence of oxide particles aligned around the weld interface. Their concentration and distribution, varying with process parameters, affect the weld integrity. The TMAZ characterised by a global loss of strength (from 334HV to 250HV) is associated with temperatures exceeding 800°C and causing γ’ and γ’’ reversion. A narrow band of the TMAZ, exposed to high strains and temperatures, showed evidences of dynamic recovery and recrystallization (up to 67% of reduction in the matrix grain size). Visual and microscopic examination of the flash layer, revealed two distinct zones. Microstructure evolution and microhardness variations were associated to process parameters and the optimum conditions for obtaining defect free weldments were determined.

Friction welding of couplings with Du+100?150 mm made of steels 20 and 15Kh5M

Production Combine Bugul'maneftemash investigated and developed friction welding technology and nondestructive control of couplings by studying the dependence of strength indices of the welded joint on the welding regime parameters. The quality of the welded joints was checked by studying the macro- and microstructures and also by x-ray examination and ultrasonic sounding. The plasticized layer formed on the separation layer, favorable for obtaining a strong weld, was studied. The mean values of mechanical properties of welded specimens are given. Ultrasonic control confirmed the high quality of the welded joints produced by the friction welding. The inner and outer fins formed during friction welding, one of the deficiencies of the method, are also studied for their effect.

軟層を含溶接継手の静的強度に関する寸法効果

In the welded joint, chemical composition and structure of weld metal or heat-affected zone which is adjacent to it are different from those of parent metal. Hence, the mechanical properties, for example stress-strain relation, of the welded joints must also be different from those of parent metal and change continuously. In this way, considering macroscopically, the welded joints are not homogeneous nor isotropic. Concerning such welded joints which are heterogeneous, it matters a great deal to investigate their strength and ductility. The welded joints are fundamentally idealized as models which are joints consisting solely of parent metal and a or hard interlayer. By soft is meant apart of welded joint in which yield point is lower than that of parent metal.In the present report, such model specimens were made by flash butt welding. The parent metal was grade S35C, the interlayer grade S10C. The specimens were given post-weld heat treatment (850°C×10 min. water quenching and 500°C×30 min. tempering) to cause an abrupt change of the mechanical properties between parent metals and interlayer. Static tensile test was made for four kinds of specimen diameter, 3, 6, 10 and 15 mm, at room temperature.In the joints including a interlayer under tension, plastic flow will begin at first in the parts of a interlayer. The transverse plastic flow of interlayer at the contact surfaces and the neighbouring zone will be held in check by the stronger parent metal, and the interlayer will be in a triaxial stress state analogous to that in the neck of tension specimen. The triaxiality will be severe with a decrease in the thickness of interlayer. The ultimate tensile strength of the joints exceeds that of the material of interlayer, if the values of thickness of interlayer are sufficiently low. The present paper describes theoretical and experimental investigations on the effect of thickness of a interlayer or specimen diameter on mechanical properties of welded specimens under static tension. The results obtained are as follows.(1) The yeild stress, ultimate tensile strength, plastic constraint factor and reduction in area of the welded joint including a interlayer are represented as functions of the relative thickness X, or the ratio of thickness of interlayer to specimen diameter, regardless of the specimen diameter.(2) The yield stress and ultimate tensile strength increase and the elongation and reduction in area decrease as the relative thickness decreases. Fracture mode becomes brittle for a sufficiently small value of X, although the material of interlayer possesses high ductility under unidirectional tension at room temperature.(3) The test results on ultimate tensile strength agree with the results of the authors' theoretical analysis for a comparatively large value of X.