Welded Samples Research Articles

Improved mechanical properties of resistance welded joints of thermoplastic composites by versatile graphene oxide

An approach of adding graphene oxide (GO) nanosheets to enhance the joints for resistance welding glass fabric reinforced polyetherimide (GF/PEI) laminates was proposed in this study. The GO nanosheets were introduced and dispersed uniformly into the heating element (HE) of carbon fiber (CF) bundles coated PEI and the welding adhesives of PEI films in the different weight ratios. The GO nanosheets were prepared firstly by the modified Hummers method. Then their morphology and structure were also confirmed by the combination of a scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction and Raman spectrometer. The lap shear strength (LSS) obtained from single lap shear specimens and fracture morphology are reported to evaluate the optimum welding parameters, such as input power, heating time and pressure. Finally, the effect of GO on the LSS of the welded samples was studied. The results showed that the LSS of joints was increased by adding GO to the welded joint, but if it exceeded the optimal value, they were more vulnerable to damage.

Influence of marine corrosion on the roughness of MAG welded joint surfaces

The study presents in the first part the behavior of the EH 36 steel with the thickness of 10 mm to MAG mechanized welding of butt-welded joints from the naval field, destructive and non-destructive testing for all welded samples. Furthermore, corrosion of the marine environment is analyzed by the electrochemical method. The study is completed with the corrosion influence on the roughness of the welded joints surfaces and conclusions.

Performance Analysis of Nano Silicon Carbide Reinforced Swept Friction Stir Spot Weld Joint in AA6061-T6 Alloy

Swept friction stir spot welding (SFSSW) is one of the preferred welding methods used in joining metals. The application of this joining process is limited by path deviation, insufficient tool plunging and vibrations caused by high torque and force during the welding. In order to improve the weld strength and weld repeatability, the optimum process parameters of SFSSW of aluminium 6061-T6 alloy were investigated through Grey rational analysis. Initially, Taguchi L16 array consisting of diameter of guide hole, tool rotational and traverse speeds was developed and experiments were conducted by filling guide hole with Silicon Carbide nanoparticles. Grey relational analysis of the experiments reports that guide hole diameter = 3 mm, rotational speed = 1600 rpm and traverse speed = 20 mm/min are found to be optimal parameters for attaining the maximum lap shear strength and hardness. The cause-and-effect analysis of data reports that the amount of SiC added to the guide hole is the most significant factor influencing the weld strength. Furthermore, mechanical and metallurgical characterisation of weld samples prepared at optimum condition were compared with neat samples. The microstructural analysis of stir zone and the fractured area were also presented. The addition of nanoparticles and use of predicted optimum weld condition results homogeneous distribution, refined grains in the stir zone that causes a noteworthy increase in the weld strength.

Stress corrosion cracking failure of friction stir welded nuclear grade austenitic stainless steel

Stress Corrosion Cracking behavior of Austenitic Stainless Steels (SS) in a chloride environment has been investigated by several methods. In this investigation failure of emerging structural material for nuclear reactor (316LN grade austenitic stainless steel) and its Friction Stir Welded (FSW) joint due to stress corrosion cracking were analyzed in a chloride environment. FSW joint was fabricated between 316LN plates with optimized process parameters. Initially, hardness and tensile properties were analyzed across the weld zone to evaluate the mechanical properties of the welded joint. Microstructural characterization of base metal (BM) and weld zone were done by Optical Microscope (OM), and Scanning Electron Microscope (SEM). Grain boundary analysis was done by Transmission Electron Microscope (TEM). Microstructural evolution revealed that the FSW process is capable to refine and reduce grain size nearby 12 times that of the base metal by Continuous Dynamic Recrystallization mechanism (CDRX). Improved strength and hardness are also recorded at the weld zone compared to the base metal. Boiling 45 wt% MgCl2 solution at constant load condition as per ASTM standard G36 was used to assess SCC failure on base metal and FSW joint. Failure due to Chloride Stress Corrosion Cracking (CSCC) on weld samples were investigated and compared with its base metal samples at different tensile stress conditions (20%, 40%, 60%, 80%, 100% of base metal yield stress values). From the experimental result steady-state elongation rate (ISS), Transition time (tss) and time to failure (tf) were evaluated and generalized equations to predict time to failure of base metal and FSW weldment was generated. The impact of microstructural morphology on SCC failure of the FSW joint was investigated. The fracture location of the weld joint, nature of crack advancement of both base metal and FSW joint was analyzed by the SEM study. A study of fracture surface displayed brittle nature transgranular failure for base metal as well as FSW samples.

Investigation of microstructure and mechanical properties of AISI2205/DIN-P355GH steel joint by submerged arc welding

• In this study, AISI 2205 duplex stainless steel materials and P355GH pressure vessel steels are joined by using the same additional metal and powder, with the same parameters and submerged arc welding method. • Welded with SAW method, these materials were tested by eye, magnetic particle and radiographic examination methods to detect surface and sub-surface defects. No pores, voids or cracks were found in the materials after the magnetic particle test and radiographic test. In addition, solid spot and fixation of the welded samples worked, and welded samples showed no unacceptable angular distortion and high-low defect error. • Tensile, bending, impact notch and hardness tests were applied to determine the mechanical properties of welded samples. When the tensile test results are examined, it is seen that although the highest tensile strength of the main materials is in AISI2205 material, % elongation values are very close to each other. • Successful results have been achieved from all SAW of duplex stainless steel and pressure vessel steels. This result shows that additional metal, welding flux and welding parameters are suitable for joining duplex stainless steel and pressure vessel steels. In this study, duplex stainless (AISI2205) steel and pressure vessel (P355GH) steel have been joined by submerged arc welding method (SAW). Three different joining operations (AISI2205-AISI2205), (P355GH-P355GH) and (AISI2205-P355GH) were performed respectively. ELOX UP 309 L submerged arc welding wire and Eliflux Bss-A submerged arc welding powder were used for joining materials. Welded materials have been tested with eye, magnetic particle and radiographic examination methods were used to detect surface and subsurface defects. Tensile, bending, Charpy impact notch and hardness tests were then performed to determine the mechanical properties of welded samples. Additionally, microstructure investigations were made to determine the structural changes in the welding zone. Various NDE technqiues were adopted to investigate the quality of the welds. As a result of tensile tests, the rupture was made of welding metal in AISI2205-AISI2205 joints and P355GH in other joints was made of base material. No visible errors were observed in the welding area after bending test. When the V-notch impact energies of the materials were compared, the highest toughness value was measured in the ITAB of AISI2205 material and the lowest toughness value was measured in the P355GH weld metal. In hardness measurements, the highest hardness value was obtained in the HAZ of the AISI2205 material, whereas the lowest hardness was measured in the P355GH base material. Microstructure studies indicated that the weld metal comprised a dendritic structure, and the grains were observed to become coarse in the region adjacent to the melting boundary on the main material side.

The influence of technological methods on the mechanical properties of welded joints obtained by friction stir welding

The article discusses promising technological methods used for the formation of dissimilar bimetallic joints in friction stir welding (FSW). The dependences of the strength characteristics on the modes FSW (the angle of inclination of the tool, the displacement of the tool from the line of contact of the welded samples, the value of the depth of the tool) are presented. The subject of the analysis is the design of the edges of the parts to be welded in the case of FSW and the step-by-step analysis of the process of obtaining butt, lap, tee, combined copper–aluminum joints, taking into account the parameters of modes welding. The article analyzes the factors affecting the strength of dissimilar joints of aluminum AD1 and copper M1 alloys, made with the help of FSW. The influence of the geometry of the prepared edges of parts on the strength of welded joints has been studied. The results of strength tests are presented, design and technological methods are recommended, aimed at improving the conditions and activating the formation of dissimilar adhesive joints.

Impact Toughness Characteristics of SM570-TMC Steel Joint Using Welding Wire Containing 0.4% Nickel at Different Level of Heat Input

The study was conducted to evaluate the impact toughness of flux-cored arc welded of SM570-TMC steel joint under different heat inputs, 0.9 kJ/mm (low heat input) and 1.6 kJ/mm (high heat input). Welding wire containing 0.4%Ni was selected on this experiment. Multi-pass welds were performed on SM570-TMC steel plate of 16 mm in thickness with a single V-groove butt joint on flat position (1G). The evaluation consists of observations on microstructure using an optical microscope and SEM-EDS, and mechanical properties including tensile, microhardness Vickers and Charpy V-notch (CVN) impact test at temperatures of 25, 0 and-20 °C. Results showed that the impact toughness of the base metal (BM) was higher than the weld metal (WM) at all test temperatures. Hardness and impact toughness of WM at low heat input was observed higher than when applied a high heat input. The welded samples at low and high heat inputs had high of tensile strength, and the fracture seemly occurs on the BM. Microstructure observation showed that at a high heat input, larger grains and microsegregation were observed. It might affect on decreasing their impact property.

Selection of friction stir welding tool rotational speed for joining dual phase DP600 steel sheets – an experimental approach

In the present work, mechanical and microstructural properties of friction stir welded similar DP600 steel were investigated. The sheets were butt welded with a single pass and three different rotational speeds such as 700, 800, and 900 rpm. The other parameters such as the tool traverse speed, tool tilt angle, and plunge depth were kept constant (50 mm/min, 2°, and 0.2 mm, respectively). The highest tensile strength of 528 MPa (82.6% of joint efficiency) was obtained for a weld sample prepared with 800 rpm and the lowest tensile strength of 350 MPa (54.7% of joint efficiency) was obtained for 700 rpm produced joint. Microstructural characterization was carried out using an optical microscope and scanning electron microscope coupled with EDAX. The planimetric method was used to find the average grain size of different stir zones. Grain size number (G) for 700, 800, and 900 rpm was found to be 12.83, 11.35, and 10.5, respectively. Microhardness tests were conducted using a micro Vickers hardness tester. The highest hardness of 345.2 HV and lowest hardness of 145.9 HV was found in the stir zone of 800 and 700 rpm, respectively. A three-point bend test was conducted for all the weld samples and the mode of failure was also analyzed using fractographic analysis.

Effect of laser welding on the mechanical and degradation behaviour of Fe-20Mn-0.6C bioabsorbable alloy

The present work aims at exploring the influence of laser welding on the functional behaviour of a Fe-20Mn-0.6C (wt.%) bioabsorbable alloy. At first, the selection of the most suitable process speed (40 mm/s) was done in order to obtain a full penetration joint with limited taper. Then, microstructural and mechanical analyses of welded sheets confirmed suitable performance of the joint, without porosity, thus preserving chemical composition, mechanical resistance and ductility even after welding. In particular, the base material comprised both γ austenite and ε martensite, while the welded samples showed a further type of martensite, namely α’. Moreover, ultimate tensile strength (1095 MPa and 1104 MPa in base and welded material, respectively) and elongation to failure (61.3% and 60.9%, respectively) were almost not influenced by the welding process. Considering the absorbable nature of these alloys, static immersion degradation tests were carried out, and confirmed that the surface of the welded bead did not exhibit a significant variation of the material degradation rate after 14 days in modified Hanks’ solution. Finally, a significant accumulation of degradation products, mainly (Fe,Mn)CO3, was observed along the joining line.

Specific features of the physicochemical properties of welded titanium nickelide

The paper analyzes the strength characteristics of welded joints made of TiNi alloy with a shape memory effect. Comparison of the level of tensile strength of welded samples made by the TIG method in an Ar and He medium was carried out using a universal machine Instron 5985. The study of the material structure was carried out on longitudinal sections using a JSM-6490LV electron microscope. The analysis of the chemical composition of the material under study in local volumes was carried out using an INCA Penta FETx3 energy dispersive attachment. The calorimetric parameters of the original and welded samples were obtained using a differential scanning calorimeter METTLER TOLEDO 822e.

The Effect of Pre Weld Heat Treatment on the Mechanical Properties and Corrosion Resistance of Artificially Aged 8011A Aluminum Alloy

In this study, 8011A aluminum alloy was subjected to artificial ageing and joined by tungsten inert gas (TIG) welding process. The effect of welding process on the mechanical (hardness, tensile, impact) properties, corrosion resistance and microstructure of the artificially aged and welded joints were investigated. The sample was divided into pre weld heat treated and as received samples. The pre weld heat treated sample was subjected to solution treatment at 500 °C, soaking for 1 hour, and quench in water before artificial ageing was carried out at 180 °C with holding time of 8 hours. Both the pre heat treated and the as received samples were welded using tungsten inert gas (TIG) welding process. It was observed from the results, that the pre weld heat treatment adopted improved the mechanical properties and corrosion resistance of the weldments in some of the properties examined. In comparison with the welded samples, the hardness, tensile yield strength and corrosion resistance of the pre weld heat treated samples were significantly improved. There was an improvement of 11% in hardness, 9% in yield strength and 92 % in corrosion resistance when immersed in 3.5 wt% NaCl solution.

Occurrence of sub-critical heat affected zone liquid metal embrittlement in joining of advanced high strength steel

Advanced high strength steels (AHSS) used in automotive structural components are commonly protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal embrittlement (LME) cracking during welding. In this study, the effect of angular welding electrode misalignment as recommended by industry was investigated and resulted in LME cracking in the sub-critical heat affected zone (SCHAZ) which is a region where LME has not been previously observed. The largest misalignment case of 6° resulted in bending of the work piece and an angled weld nugget/heat affected zone (HAZ), causing LME cracks in the lower temperature HAZ regions. SEM and EBSD analysis characterized the LME crack area as the SCHAZ and below the Ac 1 transformation temperature. Furthermore, dilatometry analysis showed the Ac 1 temperature to be approximately 660 °C, meaning LME occurred below the traditional 700 °C minimum threshold. In addition to this novel observation of LME before transformation and at low temperature, it was also noted that only misalignment beyond 2° promoted LME cracking. The low angle 2° case was observed to be statistically the same using a Student’s t -test (α = 0.05) on 6 welded samples for LME crack severity compared to a standard 0° case.

Microstructural and Mechanical Properties Evaluation of Tungsten Inert Gas-Welded 316 Stainless Steel and Pure Copper Joint

Tungsten inert gas welding of 316 stainless steel and 99.9% pure copper using nickel as filler metal was performed. The optimized process parameters adapted for the welding process are described. The microstructural studies revealed a complex heterogeneous fusion zone microstructures characterized both by rapid cooling and poor mixing of the materials which contain main elements which are mutually insoluble. Also, the welded specimen did not expose any defects such as porosity and cracks; however, some copper diffusion through the grain boundaries of steel was observed at the steel and fusion zone interface. The microhardness shows homogeneous values at the weld root and a higher hardness with more inhomogeneity at the weld face. The tensile strength of the weld sample was measured to be 143.7 MPa.

Effect of process parameters on bead geometry, tensile and microstructural properties of double-sided butt submerged arc welding of SS 304 austenitic stainless steel

The purpose of this investigation is to study the effect of welding variables on bead geometry, fusion zone profile and tensile properties of double-sided submerged arc welding on SS 304 austenitic stainless steel. The individual effect of welding parameters, i.e., welding current, voltage and traverse speed, on bead geometry and tensile properties was investigated. Both microstructural and mechanical characterizations of the weldment were carried out in the present study. It was observed that the operating parameters have significant effect on bead geometry and tensile properties. The double-sided welding effectively enhanced the weld seam ductility. The percentage of elongation is improved by 19.48% to 50.2% for double-sided samples as compared to base material. A comparative study between single and double-sided butt welding was also carried out. For single-sided sample the percentage of elongation is lower than the base material. The percentage reduction in angular distortion of 55.17% is observed with double-sided weld sample as compared to single-sided weld sample.

The role of stirring time on the metallurgical and mechanical properties during modified friction stir clinching of AA6061-T6 and AA7075-T6 sheets

In this study, the modified friction stir clinching process was successfully utilized to weld the AA7075-T6 to AA6061-T6 aluminum alloys. The approach of this study was to appraise the influence of the stirring time (6, 12, and 18 s) on the metallurgical and mechanical behavior of the welded samples. The microstructural study demonstrated that stirring time significantly affected joint properties and material flow, which can be ascribed to the discrepancy in the properties of the Al alloys used in this study. Void, local melting and defect-free joints were produced under the stirring times of 6 s, 18 s, and 12 s respectively. It was found that tensile/shear strength increased significantly from 63.5 MPa to 109 MPa as the stirring time increased from 6 s to 12 s, while a further increase in the stirring time to 18 s significantly decreased the joint’s strength to 76.1 MPa. The observed failed samples showed that stirring time did not influence fracture mode.

Conventional and underwater friction stir welded AA2024-T351 aluminium alloy – a comparative analysis

Purpose Friction stir welding (FSW) and underwater friction stir welding (UWFSW) of aluminium alloy 2024-T351 was carried out, with a chosen set of parameters, namely, rotational speed of 450 rpm, 560 rpm and 710 rpm, welding speed of 25 mm/min, 40 mm/min and 63 mm/min and tool tilt angle of 0º, 1° and 2º. This study aims to understand the correlation between temperatures and weld parameters, finite element simulation was carried out using Abaqus®. Design/methodology/approach Comparative analysis of the mechanical properties of the samples welded with FSW and UWFSW was carried out and correlated with that of the microstructures. Microhardness survey was also conducted across the weldments to support the findings. Findings Samples welded with higher rotational speed and low traverse speed favoured good quality, defect-free welds with enhanced material flow. Underwater welded samples resulted in improved mechanical properties than that of the samples welded with conventional FSW. Higher cooling rates resulted in finer grains in all UWFSW samples than that of conventional FSW samples, which, in turn, also reflected in the microhardness survey done across the weldments. Among the chosen window of the parameter, samples welded with 710 rpm, 25 mm/min and 2° had shown improvement in mechanical properties. Research limitations/implications This work was carried out in a milling machine, which limits the rotational speed which could be used. Optimistically, this limitation also paves way for using the commonly available milling to be used for FSW. Originality/value This original research study shall open opportunities to enable FSW and UWFSW to be done on similar/dissimilar joints of varying composition. Additionally, this research study throws enough light on the age – hardenable aluminium alloy being welded in a commonly available milling machine.

Pulsed laser butt welding of AISI 1005 steel thin plates

Pulsed laser welding is a joining process, which takes advantage of the laser energy quality with precise control equipment. Its characteristics allow joining thinner materials with reduced thermal distortion without filler material, fulfilling the industrial interest in this process. In the present work, AISI 1005 steel sheets of 1.7 mm thickness were subjected to different pulse Nd:YAG laser treatments to obtain one side bead-on-plate weld samples and double sided butt welds. Since the quality of the joints is strongly influenced by the process parameters, an experimental design methodology was adopted to define a suitable combination of the laser beam power, pulse duration and spot diameter. The Box-Behnken technique and response surface methodology associated with analyses of defects allowed the determination of the appropriate welding parameters. The microstructure characterisation revealed the melted fusion zones originated from the thermal effect of the overlapped pulses. Additionally, microhardness measurements at fusion zone exhibited higher values than the base material and heat affected zone, due to the hard microconstituents developed. The tensile test performed at samples extracted from double sided laser welds showed good resistance results, fracturing at the base material of joints. The present work demonstrates that pulsed laser welding methodology is suitable to obtain high quality joints of steel thin plates.

The effect of offset tools on aluminum AA6351 alloy friction stir welds

Friction Stir Welding (FSW) is a new and emerging solid-phase welding technique. Being a solid-state nature, this process offers several advantages including absent of melt related defects, low distortion, and higher weld joint strength etc., in comparison with traditional fusion type of welding techniques. Because of these numerous advantages, FSW technique is more frequently used in different industries. A non-consumable rotating tool is utilised in this process. The tip of the tool generates frictional heat while rotating on the abutting workpiece surface to complete the welding process. In this current investigation, experimental work is performed to study the effect of various offset tools on weld strength and also to compare without any offset. FSW has been done with all these tools by changing the tool’s rotational speed. The base material used in this study is five millimeter thick Aluminum AA6351 alloy. The tensile test conducted for all prepared weld samples to evaluate the better tool.

Optimization of post-weld heat treatment condition of arc-welded T91 steel tubes

Modified 9Cr–1Mo ferritic/martensitic (T91) steel tubes have been welded with gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) processes. The welded tubes have been post-weld heat-treated (PWHT) at selected temperatures (i.e., at 720 °C, 760 °C and 775 °C for different times) below their Ac1 critical temperature (~791 ± 5 °C). The PWHT microstructures, mechanical properties and fracture behavior of welded samples have been investigated. The results suggest that the PWHT temperatures closer to Ac1 critical temperature (i.e., 760 °C and 775 °C) has a strong influence on the properties of the T91 welds. They have shown uniform hardness and enhanced tensile strength and percent elongation as against as-welded and 720 °C – 120 min PWHT condition. Further investigation suggests that the strength and percent elongation for 775 °C – 30 min condition were highest among all the PWHT conditions examined. The observed variation in mechanical properties has been related with the finer microstructural features (mainly grain size and precipitate size). This work further confirms that for PWHT temperatures closer to Ac1, as the holding time increases the failure shifts from base metal (BM) to weld metal (WM) region, predominantly due to de-cohesion at the Mn, Cr, Mo rich coarse precipitate/matrix interface. From this study, a novel PWHT condition at 775 °C – 30 min is being proposed for optimum microstructure and mechanical properties for the T91 steel tube welds.

Characterization of Dissimilar Al-Cu BFSW Welds; Interfacial Microstructure, Flow Mechanism and Intermetallics Formation

Abstract The purpose of this study is to elucidate the flow features of the dissimilar Al-Cu welded plates. The welding method used is Bobbin Friction Stir Welding (BFSW), and the joint is between two dissimilar materials, aluminium alloy (AA6082-T6) and pure copper. Weld samples were cut from along the weld line, and the cross-sections were polished and observed under an optical microscope (OM). Particular regions of interest were examined under a scanning electron microscope (SEM) and analysed with Energy Dispersive X-ray Spectroscopy (EDS) using the AZtec software from Oxford Instruments. The results and images attained were compared to other similar studies. The reason for fracture was mainly attributed to the welding parameters used; a higher rotational speed may be required to achieve a successful BFSW between these two materials. The impact of welding parameters on the Al-Cu flow bonding and evolution of the intermetallic compounds were identified by studying the interfacial microstructure at the location of the tool action. The work makes an original contribution to identifying the solid-phase hybrid bonding in Al-Cu joints to improve the understanding of the flow behaviours during the BFSW welding process. The microstructural evolution of the dissimilar weld has made it possible to develop a physical model proposed for the flow failure mechanism.