Tensile Strength Of Welded Joints Research Articles

Study On Microstructures And Properties Of 7A52 Aluminum Alloy Joints In Laser-MIG Hybrid Welding

The 7A52 aluminum alloy of 10mm thickness was welded by laser-MIG hybrid welding. The microstructures and properties of the welded joints were studied. The results show that: The morphology of the weld section is “glass shape”, and the “cup body area” of the top of the weld is formed by the arc thermal melting base material, with typical MIG welding characteristics. And the “cup foot area” of the bottom weld is produced by the keyhole effect and has the characteristics of laser deep fusion welding. The Zn and Mg elements have different degrees of evaporation and loss in the MIG welding zone and laser welding zone. The hardness from the center of the weld to both sides base metal is a u-shaped distribution. The average tensile strength of welded joints reached 304.7MPa, which is 74.3% of the base material.

Microstructure and properties of electron beam welded joints of tantalum and tungsten

Electron beam welding of tantalum/tungsten was carried out. The results showed that the main defects of the joints were cracks and unfused holes with poor connection. The microstructure of the heat affected zone on the tungsten side was coarse equiaxed grains and a little amount of small equiaxed grains with straight grain boundaries near the weld. The weld only consisted of the A2 phase of tantalum-tungsten replacement solid solution. Hardness of fusion line was considerably high, and there was a great hardness gradient in the heat affected zone as well. Tensile strength of welded joints was only 56 MPa. Fracture occurred near the fusion line on the tantalum side. Besides, the fracture was a mixture of intergranular fracture, cleavage fracture, and quasi-cleavage fracture, which was the typical characteristic of brittle fracture. Welding with 0.3 mm deflection to Ta was carried out to optimize the fusion state of welded joints. Hardness of the joint was lower than that with no deflection especially of the fusion line. Tensile strength of welded joints was improved to 86 MPa.

Effect of microstructural features on the failure behavior of hybrid laser welded AA7020

AbstractDetailed investigations of microstructural feature, mechanical property, fatigue strength, and damage mechanism were conducted on hybrid laser welded 7020‐T651 aluminum alloys used into high‐speed railway vehicles. The results show that the hybrid laser welding process can induce significant changes of microstructures and alloying elements, together with numerous gas pores. Such local modifications degrade the fatigue performance. The tensile strength of welded joints was approximately 74% with respect to the base metal, thus satisfying the design standard. The fatigue property was determined in the low and high cycle regimes. It was found that the fatigue strength of welded joints was fairly inferior to that of the base metal, but far higher than the IIW recommended value. Furthermore, welding defects were well believed to contribute to the shorter fatigue life. The small fatigue crack growth presented highly discontinuous and inhomogeneous due to microstructure and porosity. By contrast, the crack stable growth stage was less sensitive to microstructural features of hybrid welded joints.

Evaluation of inhomogeneity in tensile strength and fracture toughness of underwater wet friction taper plug welded joints for low-alloy pipeline steels

The microstructural characteristics of underwater wet friction taper plug welded joints for API X52 pipeline steel were investigated and tensile strength and facture toughness of the welded joints were experimentally evaluated. The microstructure of welded joints is considerably inhomogeneous. The tensile strength of welded joints shows heterogeneity in thickness direction. All of the tensile specimens taken from upper side of welded joints fracture at base material, while those taken from the bottom are broken at bonding interface or base material. The fracture toughness of welded joints deteriorates seriously, as compared with base material. The welded joints with notches in weld center have higher fracture toughness than those in bonding zone and the axial force has few influences on fracture toughness of welded joints. The bonding zone between plug and base plate should play a role as fissure defect for the whole welded joint, considering that it is tens of microns and much softer than its vicinity. In addition, the coarse grain, quenched martensite and Widmanstätten ferrite in weld region should also be responsible for the reduction of fracture toughness.

Modeling and Optimization of Friction Stir Welding Process Parameters for Dissimilar Aluminium Alloys

Friction stir welding (FSW) is relatively new solid-state welding technique which was initially developed to weld softer material such as aluminum, zinc, magnesium, copper alloys that were extensively used in automobile and marine industries. To obtain a quality weld controlling of process parameters such as tool rotational speed, welding speed, axial force, play a major role. In this study experiments were conducted based on three factors, three-level, and Taguchi approach was applied to determine the effect of process parameters such as tool rotational speed, traverse speed and axial force on ultimate tensile strength of friction stir welded dissimilar joints of 6061 and 2024 aluminium alloys. Taguchi method was used to obtain significant and optimum levels of process parameters.Mathematical model was developed using ANOVA based Taguchi method and artificial neural network, which were further used to predict the ultimate tensile strength of friction stir welded dissimilar joints of 6061 and 2024 aluminium alloys. Rotational speed, welding speed and axial force were found significant parameters in deciding the ultimate tensile strength of the joint. The optimum value of ultimate tensile strength of welded joints obtained was 189.1 MPa at second level of process parameter. The results obtained was validated with model as well as confirmation test. ANN model was found to be more accurate in ultimate predicting tensile strength than Taguchi method.

Microstructure and Mechanical Properties of Electron Beam‐Welded Joints of Titanium TC4 (Ti‐6Al‐4V) and Kovar (Fe‐29Ni‐17Co) Alloys with Cu/Nb Multi‐Interlayer

Electron beam welding of a titanium alloy (Ti‐6Al‐4V) and a kovar alloy (Fe‐29Ni‐17Co) was performed by using a Cu/Nb multi‐interlayer between them. Microstructure and composition of welded joints were analyzed by means of optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X‐ray diffraction. Mechanical properties of welded joints were evaluated by microhardness and tensile strength tests. Results indicated that in case of 0.22 mm thickness of Nb foil, microstructure of the titanium alloy side was mainly composed of Ti solid solution and some intermetallic compounds such as FeTi and CuTi2, whereas in case of 0.40 mm thickness of Nb foil, the appearance of weld was more uniform and hardness of the weld zone decreased sharply. However, tensile strength of welded joints was increased from 88.1 MPa for the 0.22 mm Nb foil to 150 MPa for the 0.40 mm Nb foil. It was found that thicker Nb foil could inhibit diffusion of Fe atoms towards the titanium alloy side, thus promoting the formation of Ti solid solution and a small amount of CuTi2 and eliminating FeTi. In addition, in both cases, Cu0.5Fe0.5Ti was found in the fusion zone of the titanium alloy side, which had an adverse effect on mechanical properties of welded joints.

Evaluation of microstructure and mechanical properties of P91 steel weldment due to addition of boron trioxide into flux during submerged arc welding

The present investigation studied the effect of boron trioxide (B2O3) addition into flux on the microstructure and mechanical properties of modified 9Cr-1Mo (P91) steel in submerged arc welding (SAW) process. Boron trioxide powder was mixed with commercial flux in different ratios to change the weld metal chemical composition. Optical emission spectroscopy results showed that weight percentage of boron varies from 0.00 to 0.0068 with the addition of boron trioxide into welding flux. Weld metal microstructure without the addition of boron reveals the presence of tempered martensite and ferrite phase, whereas boron-added microstructures highlighted the dominating nature of tempered martensite. Scanning electron microscope analysis also showed that the dispersed carbides especially M23C6 were increased with the addition of boron. Weld metal macrohardness profile reveals that boron has the significant effect on the weld metals. The maximum hardness of 342 HV was found for the 12.5% B2O3, whereas weld of without boron shows the hardness of 240.8 HV. Boron addition has a positive effect on the tensile strength of weld joints except for the 12.5% B2O3. But the toughness of weld zone decreases with the addition of boron.

Nd:YAG laser micro-welding of ultra-thin FeCo–V magnetic alloy: optimization of weld strength

Abstract The main aim of this research is to optimize the tensile strength of laser welded FeCo–V alloy. A mathematical relationship was developed to predict tensile strength of the laser beam welded FeCo–V foils by incorporating process parameters such as lamping current, welding speed, pulse duration and focused position. The procedure was established to improve the weld strength and increase the productivity. The results indicate that the pulse duration and welding speed have the greatest influence on tensile strength. The obtained results showed that the tensile strength of the weld joints increase as a function of increasing pulse duration reaching to a maximum at a pulse duration value of 2.25 ms. Moreover, the tensile strength of joints increases with decrease in welding speed reaching to a maximum at a welding speed of 125 mm/min. It has been shown that increase in pulse duration and decrease in welding speed result in increased effective peak power density and hence formation of more resistant welds. At higher pulse durations and lower welding speeds, the tensile strength of weld joints decreases because of formation of solidification microcracks in the fusion zone.

Optimization of Operational Parameters in Friction Stir Welding of AA7075-T6 Aluminum Alloy Using Response Surface Method

Response surface methodology was employed to optimize effective factors during friction stir welding of AA7075 aluminum alloy. The effect of operational parameters on the ultimate tensile strength of welded joints was studied. Five levels of the tool rotation speed, the welding speed, the shoulder diameter, and the pin diameter in the range of 350–650 rpm, 35–95 mm/min, and 12–18 and 4–6 mm were investigated using a central composite design. In order to have rotatable and orthogonal design, 36 experiments consisting of 12 center points were conducted. Moreover, the distance of each axial point from the center point was 2. All welded joints were defect free. The statistical model showed that the welding speed and the rotation speed compared to the shoulder diameter and the pin diameter have greater impact on the response. It was found that the joint efficiency of 85% was achievable under the intermediate rotational speeds and the high welding speeds using a tool with the moderate shoulder diameters and the large pin diameters. The joint produced using the rotation speed of 513 rpm and the welding speed of 95 mm/min, the shoulder diameter of 16.1 mm and pin diameter of 5 mm yielded the highest joint strength. This joint had a joint efficiency of about 94%.

Influence of heat input on HAZ liquation cracking in laser welded GH909 alloy

In this paper, we describe influence of heat input on HAZ liquation cracking in laser welded GH909 alloy. The results demonstrated that more cracks were produced using high laser power and welding speed. The presence of cracks greatly weakened the hot ductility of this material and the binding force between the adjacent grains, resulting in reducing the tensile strength of welded joints. The occurrence of HAZ cracking was mainly attributable to the coarseness of microstructures and large tensile stresses. A new method was proposed to prevent HAZ liquation cracking using low laser power and welding speed at a constant heat input. The simulated results were consistent with the experimental results, verifying the correctness and feasibility of the method.

Influence of flash butt welding parameters on microstructure and mechanical properties of HSLA 590CL welded joints in wheel rims

Abstract

An Experimental Study on the Tensile Behaviors of Ultrasonic Welded T-joints for Polyamide Composite

In this paper, an experimental investigation on ultrasonic welding of polyamide composites reinforced with glass fiber has been carried out. The effect of ultrasonic welding parameters, such as welding time, air pressure, hold time and the amount of glass fiber in the composite on tensile strength of weld joints were determined using response surface methodology. This methodology was applied for developing a mathematical model which can predict the main effects of the above parameters and their impacts on tensile strength of T-welded ultrasonic joints in 4-mm thick polyamide composite sheets. The analysis of variance was performed to check the adequacy of the developed model. A comparison was also made between the predicted and actual results. The results showed that a maximum failure force of about 4759 N is obtained when vibration amplitude, air pressure welding time, holding time and amount of glass fiber are 35 microns, 3.6 bar, 1.84 seconds, 0.9 seconds and 41 percent, respectively .The joint strength of welded parts increased with the fiber content in the composites.

Electron Beam Welding of High Strength Quenched and Tempered Steel

The paper deals with the investigation of microstructure and mechanical properties of electron beam welded joints of high strength steel grades S690QL and S960QL in quenched and tempered condition. The microstructure of base metal was composed of bainite and martensite mixture at hardness about 270HV10 and 340HV10 for the S690QL and S960QL steels, respectively. The weldment was composed of several characteristic subzones revealed on the transverse sections. The central region of the weldment consisted mainly of coarse columnar dendritic grains which perpendicular to the fusion zone boundary. The microstructure of the heataffected zone near the fusion line consisted mainly of martensite, however, in both steels the microstructure varied with the distance from the fusion line. The tensile strengths of welded joints were Rm=850 MPa (S690QL) and 1074MPa (S960QL) and corresponded the tensile strengths of the base materials.

Characteristics of Welding Crack Defects and Failure Mode in Resistance Spot Welding of DP780 Steel

The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested, and three different types of welding cracks in welded joints were investigated by optical microscopy, scanning electron microscopy and electron back-scattered diffraction. Finally, the failure mode of the welded joints in shear tensile test was discussed. It is found the shear tensile strength of welded joints can be greatly improved by adding preheating current or tempering current. The surface crack in welded joint is intergranular fracture, while the inner crack in welded joint is transgranular fracture, and the surface crack on the edge of the electrode imprint can be improved by adding preheating current or tempering current. The traditional failure mode criterion advised by American Welding Society is no longer suitable for DP780 spot welds and the critical nugget size suggested by Pouranvari is overestimated.

Analisa Kekuatan Tarik pada Sambungan Las Baterai terhadap Kekuatan Arus Listrik Baterai

Research analysis of the tensile strength of the weld on the battery to power an electric current battery has been done. The goal is to determine the tensile strength of welded joints using welding batteries with a variable flow battery, the thickness and diameter of the test material. Research methodology, including: (1) assemble welding battery (battery consists of 3 pieces) with the desired total current is 60 A, 80 A and 120 A, (2) arranging charging the battery and welding handle bar positive and negative, (3 ) welding on iron plate with thickness 4mm, 6mm and 8 mm with a current 60 A, 80 A and 120 A, (4) on an iron rod diameter 8mm, 10mm, and 12 mm with a current 60 A, 80 A and 120 A. The results showed the shape of specimens of iron, welding tools and strong currents thickness / diameter significantly influence the tensile specimens welded with welding tools batteries. The best treatment to iron rod the current round is 60 A at 8 mm diameter tensile yield amounted to 11.65 kg/mm2. The best treatment for the current iron plate is 80 A at 8 mm thick plate produce a tensile strength of 38.2 kg/mm2. From the calculation of economic, investment and operational costs-making tools, welding batteries cheaper than welding inventer and welding dynamo. However, welding batteries can not be regulated the size of the battery current.

Microstructural characteristics and mechanical properties of underwater wet flux-cored wire welded 316L stainless steel joints

Underwater wet welding of 316L stainless steel was performed with specially designed nickel-based tubular wire at shallow water. Microstructural observations showed that fully austenitic weld metal without cracks and pores was achieved by the nickel-base filler materials. The ultimate tensile strength of welded joints was 508MPa and the average elongation of the joints was up to 32%. The impact test results indicated that all specimens exhibited ductile fracture and Charpy impact toughness value of weld metal at 0°C was 159J/cm2. The average hardness of weld metal was 156HV. There was a sharp increase of hardness occurred in fusion zone due to more ferrite formation.

Characterization of the tensile properties of friction stir welded aluminum alloy joints based on axial force, traverse speed, and rotational speed

Friction stir welding (FSW) process has gained attention in recent years because of its advantages over the conventional fusion welding process. These advantages include the absence of heat formation in the affected zone and the absence of large distortion, porosity, oxidation, and cracking. Experimental investigations are necessary to understand the physical behavior that causes the high tensile strength of welded joints of different metals and alloys. Existing literature indicates that tensile properties exhibit strong dependence on the rotational speed, traverse speed, and axial force of the tool that was used. Therefore, this study introduces the experimental procedure for measuring tensile properties, namely, ultimate tensile strength (UTS) and tensile elongation of the welded AA 7020 Al alloy. Experimental findings suggest that a welded part with high UTS can be achieved at a lower heat input compared with the high heat input condition. A numerical approach based on genetic programming is employed to produce the functional relationships between tensile properties and the three inputs (rotational speed, traverse speed, and axial force) of the FSW process. The formulated models were validated based on the experimental data, using the statistical metrics. The effect of the three inputs on the tensile properties was investigated using 2D and 3D analyses. A high UTS was achieved, including a rotational speed of 1050 r/min and traverse speed of 95 mm/min. The results also indicate that 8 kN axial force should be set prior to the FSW process.

Ultrasonic Impact Treatment to Improve Stress Corrosion Cracking Resistance of Welded Joints of Aluminum Alloy

Stress corrosion cracking is one of the major issues for welded joints of 6005A-T6 aluminum alloy in high-speed trains. High residual stress in the welded joints under corrosion results in stress corrosion cracking. Ultrasonic impact treatment was used to control the residual stress of the welded joints of 6005A-T6 aluminum alloy. Experimental tests show that ultrasonic impact treatment can induce compressive longitudinal and transverse residual stress in the welded joint, harden the surface, and increase the tensile strength of welded joints. Salt-fog corrosion tests were conducted for both an as-welded sample and an ultrasonic impact-treated sample. The surface of the treated sample had far fewer corrosion pits than that of the untreated sample. The treated sample has higher strength and lower tensile residual stress than the untreated sample during corrosion. Therefore, ultrasonic impact treatment is an effective technique to improve the stress corrosion cracking resistance of the welded joints of 6005A-T6 aluminum alloy.

Influence of aging temperature on strength and toughness of laser-welded T-250 maraging steel joint

This paper presents an investigation on the strength and toughness of laser-welded T-250 maraging steel joint, aimed at elucidating the influence mechanism of aging temperature on microstructures and mechanical properties of the joints. The results showed that as the aging temperature increased, the ultimate tensile strength of welded joints increased, reaching a maximum of 1640.5MPa at 520°C, and then decreased. The static toughness of welded joints decreased at first and increased later with the aging temperature increasing. The minimum of 38.8MJm−3 for the static toughness was obtained at 560°C. There were two types of reverted austenite respectively distributing in grain boundaries and in the matrix of martensite, due to the change of aging temperatures. This study underscores that the Ni3(Ti, Mo) precipitate and reverted austenite are the critical factors influencing the strength and toughness of welded joints. The Ni3(Ti, Mo) precipitate in the weld metal improves the strength of welded joints remarkably as its volume fraction increases. The reverted austenite in grain boundaries is harmful to the toughness of welded joints, while the reverted austenite in the matrix is beneficial to the toughness of welded joints because of its finely dispersive distribution and its ability to prevent crack propagation. Increasing the amount of reverted austenite in the matrix is an effective way to improve mechanical properties of laser-welded maraging steel joints.

Study on laser-MIG hybrid welding characteristics of A7N01-T6 aluminum alloy

In this paper, an experimental study of laser-metal inert gas (MIG) hybrid welding of A7N01-T6 aluminum alloy in butt joint configuration was carried out. Visual examination and optical microscope were utilized to study the macro profile and microstructure, while mechanical properties of the welds were evaluated with the help of a tensile test and microhardness measurement. The joints were evaluated by the scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Besides, X-ray microtomography was employed to characterize the morphology, quantity, and distribution of porosities in the weld seam. The results revealed that 4-mm thickness high-quality laser-arc hybrid welding butt joints were obtained with parameters of laser power 3.5 kW, welding speed 4 m/min, and welding current 140 A. The average tensile strength of welded joints reached 268 MPa, 76.6 % of that of the base metal. The loss was likely to be related to the presence of micropores, and further three-dimensional characterization indicated that there were altogether 4326 pores with diameters ranging from 0.1 to 79 μm in the tested sample, accounting for 0.57 % of the volume fraction and 4.56 % of the cross-sectional area fraction at the most. The existence of porosities, the dissolution, and coarsening of strengthening precipitates together promoted the joint softening in A7N01-T6 hybrid welding process.