Microstructure Of Welded Joints Research Articles

Research on Microstructure and Mechanical Properties of Square Wave Alternating Current Tungsten Inert Gas Welded Joints in 2219-T6 Aluminum Alloy

Research on Microstructure and Mechanical Properties of Square Wave Alternating Current Tungsten Inert Gas Welded Joints in 2219-T6 Aluminum Alloy

Study of fatigue crack growth characteristics of TIG welded AZ31B magnesium alloy joint based on laser bionic treatment

AbstractIt is crucial to obtain better fatigue property for the safe application of materials, while nature provides new structural design ideas for effectively improving fatigue property. In this study, a “soft‐hard” alternating bionic structure was fabricated on the surface of TIG welded AZ31B Mg alloy joints by laser bionic treatment (LBT). Microstructure of welded joints was tailored by LBT, resulting in fine equiaxed grains with random orientations and increased microhardness. The fatigue crack growth threshold of the welded joints with bionic structure is increased by more than 40%, and crack growth rate was lower. LBT could significantly affect crack growth behavior and presented obvious crack deflection, resulting in a rougher fracture surface and more second cracks and branches. LBT significantly improved the fatigue crack growth resistance, inducing a series of strengthening mechanisms. The present work opens a new alternative to improve the fatigue properties of welded joints.

Microstructure evolution and mechanical properties of wrought/wire arc additive manufactured Ti-6Al-4V joints by electron beam welding

Wrought-additive hybrid manufacturing technology effectively combines the advantages of high efficiency of traditional manufacturing and high flexibility of additive manufacturing technology. Mechanical Properties of welded joints is the key to evaluate the performance of parts. In this study, the wire and arc additive manufacturing (WAAM) Ti-6Al-4V alloy was successfully connected with the wrought Ti-6Al-4V plate by electron beam welding (EBW). The effect of welding direction on microstructure and tensile properties of welded joints was studied. The results show that a large amount of needle martensite α’ phases exists in the joint due to the rapid cooling rate. The mechanical properties tests show that compared with the Wrought + SD (Scanning direction) sample, the Wrought + BD (Building direction) sample has higher tensile strength, but lower elongation. All samples fractured at the WAAMed Ti-6Al-4V side, which was related to the initial state of the WAAMed Ti-6Al-4V sample. The experiment also explored the fracture mechanism by TEM, which involved the nucleation, growth of cracks caused by vertical dislocation accumulation at the α/α’ phase interface, and occurrence of the displacement of the α (or α’)/β phase interface caused by the parallel dislocations.

Influence of cooling conditions on the microstructure and impact strength of welded joints made by automatic submerged multi-arc welding

The aim of the work was to study the effect of cooling rate on the formation of the structure and impact strength of a welded joint of 0,07C-1,6Mn-0,2Cr-Nb pipe steel. The cooling rate w8/5 was varied from 0.9 to 12.4 °/s in the temperature range of 800–500 °/s by changing the heat input of welding, the groove width, and the temperature of 22 mm thick plates welded on a laboratory welding stand. The conducted studies confirm the previously obtained results on the weldability of pipe steels, that a decrease in the heat input of welding and, as a result, an increase in the cooling rate of the w8/5 welded joint is accompanied by an increase in impact toughness. For the studied steel, a significant increase in the impact toughness of KCV-40 (more than 2.5 times) occurs in the range of cooling rates w8/5 from 0.9 to 7.3 °/s and is typical not only for tests along the fusion line, but also in the center of the seam weld. It is shown that with an increase in the cooling rate of the welded joint in the structure of the weld metal, the maximum length and width decrease, and, at the same time, the proportion of grain boundary ferrite crystallites. At high cooling rates, the matrix of the weld structure consists entirely of acicular ferrite, which is favorable in terms of increasing the density of high-angle grain boundaries, toughness, and cold resistance. In the heat-affected zone, with an increase in the cooling rate, the maximum and average grain sizes decrease; grain-boundary and Widmanstatt ferrite is eliminated; a completely bainite structure is formed and the proportion of lath bainite increases, which also leads to an increase in the density of high-angle boundaries and contributes to an increase in impact strength. With an increase in the cooling rate, the proportion of the MA-constituents in the structure of the seam and the HAZ are increases. It is assumed that an increase in the cooling rate, simultaneously with a favorable effect on the structure of the weld and the weld pool, reduces the time for the processes occurring in the weld pool, which can be an unfavorable factor in terms of the toughness of the weld.

Effect of welding parameters on the mechanical and metallurgical properties of armor steel weldment

The effect of welding parameters on the mechanical and metallurgical properties of armor steel weldment was studied using gas tungsten arc welding process with two filler wires: carbon steel and austenitic stainless-steel filler wires (AWS A5.18 ER 70S-6 and AWS A5.9 ER 307, respectively). The joint configurations were mainly single V and single bevel grooves. Using both AWS A5.18 ER70S-6 carbon steel filler wire and AWS A5.9 ER307, austenitic filler wire for the two joints passed the required tensile strength by the military standard. The joints successfully regained the base metal hardness at a distance of less than 15 mm. The ultimate tensile strength of the joints welded in a single bevel groove is 906 MPa which is higher than the joints welded using a single V groove is 865 MPa. This could be attributed to the increase in dilution percentage with the single bevel joints. Both single V joint and single bevel joints passed the required Charpy V-notch impact test whether using both carbon and stainless-steel wires. The effect of heat input and cooling rate on the mechanical and microstructure of welded joints was studied. The reduction of heat input caused a narrow HAZ with a small reduction in its hardness values with much reduction in the width of softening microstructure zone. SEM observations show that the base metal has a martensitic structure, but the weld metal microstructures depend on the filler: carbon steel or austenitic steel types. Using a single bevel groove with an austenitic steel filler metal, the weld metal shows a martensitic/austenitic microstructure by SEM observation, and this was verified by the Schaeffler diagram which showed a high dilution percentage (about 35% dilution). This resulted in a significant increase in joint strength and a higher weld metal impact resistance.

Arc Characteristics and Welding Process of Laser K-TIG Hybrid Welding

The Q235 steel plate butt joint was successfully welded by the laser K-TIG hybrid welding method. The effects of hybrid welding process parameters such as welding current, the distance between heat sources, laser power, laser defocusing amount, and welding speed on the coupled arc profile and welding process stability were studied. The results indicated that the laser deflects the K-TIG arc, and the deflection angle becomes smaller as the arc current increases. After K-TIG generates small holes, if the laser beam acts on the bottom of the keyhole, the welded depth can be further increased; however, the laser power has little effect on the welded depth. The distance between heat sources is the main factor affecting the state of laser-arc coupling. Optical microstructures of welded joints showed that the grains in the arc zone were coarser than those in the laser zone, and there are more columnar crystals in the fusion zone. The microhardness of the weld center is significantly higher than that of the base metal, up to 220 HV. At the same time, the change of tensile strength of the weld under the influence of a single parameter was analyzed, and it was found that tensile properties of the weld first increased and then decreased with the increase of K-TIG arc current I, heat source distance D, and welding speed V, respectively. With the increase of laser power P, it first decreased and then increased, and with the increase of laser defocusing amount δf, it showed a downward trend.

Influence of Nano-Sized Al2O3 Nanoparticles and Multipass FSW on Microstructure and Mechanical Characteristics of Dissimilar Welded Joints of AA6061 and AA5083

Influence of Nano-Sized Al2O3 Nanoparticles and Multipass FSW on Microstructure and Mechanical Characteristics of Dissimilar Welded Joints of AA6061 and AA5083

TAGUCHI OPTIMISATION ON EFFECT OF WATER ENVIRONMENT IN JOINING DISSIMILAR AL5083 AND AL6061-T6 ALUMINIUM ALLOY USING FRICTION STIR WELDING

Water cooling has the potential to improve the mechanical qualities of weldment joints in butt welding configurations. However, the joining procedure on such a configuration faces a challenging defect-free joining issue with the standard approach. This project investigates the effect of welding conditions on the joint quality using three different tool pin profiles (cylindrical straight, cylindrical threaded and tapered cylinder) during dissimilar underwater friction stir welding of a 6 mm thick plate. An experimental method following Taguchi parametric design is carried out to optimise the technique on hardness and microstructure at the weld nugget. ANOVA is used to assess the effect of each process parameter, namely tool pin profiles, welding speed, welding speed, and hardness responses. The water environment approach lowers thermal flow by maintaining consistent temperature from tool pin profiles. The combination of ongoing process parameters and fast-cooling rate induced heat input improves the welded joint's mechanical characteristics and microstructural grain. The experiment revealed the appropriate process parameters of 900 rpm, 60 mm/min, and tapered cylinder pin profile. Consequently, water-cooling significantly contributes to welded joints' mechanical properties and microstructure at the optimal parameter level, resulting in improved strength performance.

Study of the microstructure and mechanical property relationships of gas metal arc welded dissimilar Hardox 450 and S355J2C+N steel joints

This research reports the investigation of the dissimilar welding of Hardox 450 and S355J2C+N steels, which have two different superior properties, by the gas metal arc welding (GMAW) method in terms of microstructure and mechanical properties. Experiments were performed using mechanical tests such as Vickers microhardness (HV 0.1), bending, Charpy V-Notch impact, wear, and tensile test. Optical microscopy (OM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analyzes have been implemented. A variation in the welded joint microstructure was observed, which affect the mechanical properties. Grain size distribution in area fraction was determined from the EBSD maps of S355J2C+N steel, welded zone, heat affected zone (HAZ) and Hardox 450 steel. The hardness value was measured 311 ± 8 HV for Hardox 450 base material. While the hardness of the S355J2C+N base metal was ∼187 ± 8 HV, the hardness of the weld center was measured as 249 ± 8 HV. Mechanical strength analysis revealed that the yield strengths of base metals were 513 ± 8 MPa and 1464 ± 8 MPa for S355J2C+N and Hardox 450, respectively. The highest tensile strength of the sample extracted from the longitudinal direction of the welded joint is 899 ± 8 MPa. The highest tensile strength of the transverse sample, which was subjected to the tensile tests, was determined as 699 ± 7 MPa and it fractured from the S355J2C+N steel which has less strength. The joint efficiency was determined as ∼133%. The weld zone has sufficient toughness and the change in toughness values in the HAZ is small. The grain size increased from martensitic Hardox 450 steel region to S355J2C+N region, in addition to this, the hardness decreased with the effect of transition from martensitic structure region to ferritic structure region. The welding zone is compatible with two different materials and has a high plastic deformation capability. With the welding procedure followed in the study, Hardox 450 and S355J2C+N dissimilar materials were successfully combined, and it was determined that this welded joint was scientifically and industrially applicable.

Coupling effect of axial ultrasonic vibration and tool thread on the microstructure and properties of the friction stir lap welding joint of Al/Mg dissimilar alloys

In this study, three tools with different thread characteristics were designed for the ultrasonic-assisted friction stir lap welding (UAFSLW) of a 3-mm-thick 6061-T6 aluminum alloy and an AZ31 magnesium alloy. The coupling effect of different thread characteristics and axial ultrasonic vibrations on the size, amount, and distribution of intermetallic compounds (IMCs) and the tensile-shear strength of welded joints was analyzed. Experimental results confirmed the formation of IMCs in the stir zone (SZ) and the bottom interface in the SZ in all joints, with Al3Mg2 predominating in the Al-Mg configuration (in which the 6061-T6 aluminum and AZ31 magnesium alloys were placed at the upper and lower plates, respectively) and Al12Mg17 predominating in the Mg-Al configuration (in which the alloys on the upper and lower plates were reversed). The bottom interfaces of the joints in the Mg-Al configuration were tortuous, forming a mechanical interlocking structure; consequently, the joints welded in the Mg-Al configuration exhibited higher tensile-shear strength than those welded in the Al-Mg configuration. Furthermore, the tool with a variable-pitch thread pin achieved welds with excellent tensile-shear strength in both the configurations (223.2 and 268.3 N/mm in the Al-Mg and Mg-Al configurations, respectively). This performance improvement was attributed to the strong coupling of the tool with axial ultrasonic vibrations, which enlarged the mixing zone and increased the uniformity of the IMCs distribution in the joints.

Microstructure and mechanical properties of 2A12 aluminum alloy welded joint through CMT double side welding

In this work, the cold metal transfer (CMT) double side welding was carried out to weld 2A12 aluminum alloy plate. The influence of the heat input on the weld appearance was studied, which indicated that when the heat input was exceeded to 651.75 J/mm the better weld appearance was obtained. Through the scanning electron microscope (SEM), electron back-scatter diffraction (EBSD) and tensile testing, the microstructure and mechanical properties of welded joints were investigated. The results showed that the size of microstructure in the front weld seam was less than that of the back weld seam due to the secondary thermal cycle. With the increases of heat input, the average grain size and elongation of welded joints were increased, the tensile strength of welded joints was reduced. The strength coefficient of welded joint was about 70%. The fracture model of welded joint belonged to ductile fracture.

Microstructure evolution and mechanical properties of SUS301L stainless steel sheet welded joint in ultrasonic vibration assisted laser welding

Ultrasonic assisted laser welding (ULW) is a newly developed welding method. In this paper, a new kind of ultrasonic assisted laser welding method, which is named trailing ultrasonic assisted laser welding (T-ULW) is proposed. First, the welding temperature fields as well as the weld pool temperature evolution in trailing ultrasonic assisted laser welding (T-ULW) and conventional laser welding (LW) are numerically simulated, and the shapes of the molten pools during T-ULW and LW are observed by a high-speed camera monitoring system. Both the simulation and monitoring results show that ultrasonic can reduce the temperature gradient of the weld pool and prolong the solidification time. Then, such three kinds of welding methods as T-ULW, common fixed-position ultrasonic assisted laser welding (F-ULW) and LW are used to weld SUS301 stainless steel sheet with a thickness of 0.6 mm respectively, and their performances are comparatively investigated by analyzing the experimentally-obtained macro morphologies, microstructures of welded joints. Macro morphology analysis results show that ultrasonic vibration not only elongates the molten pool, but also changes the cross-sectional shapes of the welds in such a way that decreases the top width and increases the bottom width. Microstructure analysis results indicate that the fusion zone of the welds obtained by T-ULW is uniformly distributed mainly by the refined equiaxed grains. Subsequently, the crystal refinement mechanisms of the welds in ultrasonic-assisted laser welds of SUS301 stainless steel are theoretically analyzed and experimentally verified, which show that due to ultrasonic disturbance, the temperature gradient of the molten pool is decreased, a stress field is generated in the welds and a so-called ultrasonic cavitation effect is produced in the molten pool. Such three mechanisms play very important roles in refining crystals in different ways that the decreased temperature gradient provides a good nucleation condition for the growth of equiaxed dendrite, and both the generated stress and ultrasonic cavitation cause the grain boundary to fracture, thereby form more new grain boundary, which finally lead to form fine and uniform grains in the welds. Finally, the mechanical properties of the joints are measured, and the results demonstrated that ultrasonic assisted laser welding especially T-ULW enables not only to increase the tensile strength of the welds, but also to improve the ductility of the welds.

Microstructural Evolution and Mechanical Properties of FCAW Joints in 9% Ni Steel Prepared with Two Types of Ni-Based Weld Metals

The microstructural and mechanical evaluation of 9% Ni steel with flux-cored arc welding (FCAW) was performed with two different Ni-based weld metals: Inconel 625 and Hastelloy 609. The weld metals showed microstructural changes depending on the temperature gradient and crystal growth rate for each region during the cooling after welding. A cellular/planar growth was exhibited at the bottom of the weld metal, which was rapidly cooled in contact with the cold base metal. Columnar dendrites were exhibited in the central region that cooled relatively slowly, and precipitates were observed in the interdendritic region. The weld joints between the base metal and weld metal have a compositional transition region due to dilution. The transition region comprised a martensite layer and a γ-phase cellular/planar layer, according to the compositional distribution. In the low-temperature toughness test, the absorbed impact energies were 89 and 55 J for Inconel 625 and Hastelloy 609, respectively. When Inconel 625 is used as the weld metal compared to Hastelloy 609, the high content of the γ-stabilizer and martensite start temperature decreasing elements leads to the formation of a thicker γ-phase layer and thinner martensite layer in the transition region. In addition, the high content of these elements suppresses the martensite transformation and maintains the stability of the weld joint interface even at low temperatures, resulting in the higher absorbed impact energy. The microstructure of weld joints and its influences on mechanical properties help to improve the practical application of 9% Ni steel FCAW.

Study on the weld formation, microstructure and mechanical properties of AZ31B Mg alloy in AC/DC mixed gas tungsten arc welding process

In this work, a new welding electrical signal waveform of the AC/DC mixed waveform is purposed to improve the welding quality of magnesium alloy TIG. The method is named as AC/DC mixed tungsten inert gas arc (MIX-TIG) welding. The AZ31B Mg alloy welded joints were obtained by AC-TIG and MIX-TIG. Through investigation of the weld formation, microstructure and mechanical properties of welded joints, the results showed that when the welding current of 90A∼110 A, the completely penetration of welded joints could be obtained. There was no obvious difference for the geometrical parameters of the weld cross-section between the AC-TIG and MIX-TIG. The microstrcuture of fusion zone consisted of α-Mg matric and β-Mg17Al12 phase. At the same welding conditions, the average grain size and β phase number in the MIX-TIG were less than that of the AC-TIG. The microhardness of the AC-TIG fusion zone was slightly larger than that of the MIX-TIG owing to the increase of β phase number. The strain of the AC-TIG welded joint was reduced by approximately 24% compared with that of the MIX-TIG welded joint.

Study on quality of low alloy high strength steel Q345 weldment

Abstract In this paper, the temperature, microstructure, residual stress and welding deformation of typical welded joints of low alloy high strength steel are calculated by using the finite element software SYSWELD. The temperature, microstructure and residual stress of Q345 low alloy high strength steel welded joint by single pass remelting and two pass remelting were numerically simulated, and the accuracy of the finite element model was verified by experiments. The numerical simulation results based on Satoh model show that the formation process and evolution mechanism of residual stress in Q345 steel at different hot temperatures. The single pass remelting weld of Q345 steel is mainly bainite with an average hardness of 310hv. The microstructure of HAZ consists of bainite, ferrite, pearlite and a small amount of martensite. With the increase of fusion line distance, the hardness of the base metal decreases. The microstructure of the base metal is ferrite and pearlite, and the average hardness is 167hv.

Investigation on joining high borated stainless steels through electron beam welding technology

High borated stainless steels (HBSSs) are widely used in nuclear field because of excellent neutron-shielding ability. However, coarse network-like borides are prone to be formed in weld joints during welding process, deteriorating the ductility seriously. In this work, electron beam (EB) welding was adopted to join ∼3.5 mm thick HBSSs containing 0.30–2.12 wt. % boron. Benefiting from high energy density, fine γ-Fe matrix and network-like borides were obtained in fusion zone (FZ) and partially molten zone (PMZ) of weld joints. The effects of boron content, heat input and post weld heat treatment (PWHT) on the microstructure, mechanical properties and fracture behaviour of weld joints were investigated. As boron content increased, narrower PMZ was observed in weld joints owing to smaller solidification temperature range. The volume fraction and size of borides in PMZ/FZ raised, enhancing the strength and decreasing the ductility. Meanwhile, the fracture location of weld joints was closer to the interface of PMZ and base metal (BM) during deformation. Higher heat input brought a wider PMZ and larger penetration depth, but hardly changed the size and distribution of borides. Interestingly, it caused a steep slope of interfacial line between PMZ and BM, leading to the fracture along the interface with low ductility. After PWHT, the borides in PMZ/FZ were spheroidized, and the stress localization during deformation was weakened. Consequently, excellent weld joints exhibiting similar mechanical properties with base steels were produced. This systematic work provided a reference for welding other materials containing coarse and brittle secondary phases.

RETRACTED: Influence of rotation speeds on microstructure and mechanical properties of welded joints of friction stir welded AA2014-T6/AA6061-T6 alloys

This study presents the joining process of plates with thickness of 4 mm in AA2014 and AA6061 through Friction Stir Welding (FSW) process under alternative tool rotating speeds. AA2014-T6 and AA 6061-T6 alloys were friction stir welded with cylindrical eased pin tool at different revolving speeds such as 700, 900 and 1100 rpm and constant welding speed of 50 mm/min. Mechanical behavior of the FSW of an aluminum alloy exposes a key role of the microstructure. The microstructure change in the interfacial region is characterized using Optical Microscopy (OM). The average grain size was determined based on ASTM E112 – 12 standards. The mechanical properties like tensile strength, micro hardness, and flexural strength of the dissimilar aluminum alloys were evaluated. The fracture examination of the tensile samples was evaluated using Scanning Electron Microscope (SEM). Distance Amplitude Curve (DAC) shows that no recordable internal discontinuities are observed for all three weldments. Further, the study articulated that the effect of rotational speed (900 rpm) exhibits better hardness, tensile and flexural strength. In addition, there was a significant improvement in the grain structure and the average % of grain structure with an average grain size was found to be 15.6 µm and it directly influences the mechanical properties.

Experimental study on application of gas metal arc welding based regulated metal deposition technique for low alloy steel

ABSTRACT In this work, a modified and advanced welding technique named regulated metal deposition (RMD) has been implemented for joining ASTM A387-11-2 low alloy steel plates. Mechanical behavior and microstructure of welded joints have been experimentally investigated after the recommended heat-treatment process. The microstructures of welded joints were examined using optical and scanning electron microscopes. Optical microscopy indicated the existence of bainitic and martensitic phases in the base material and weld zone, respectively. Scanning electron microscopy combined with energy dispersive x-ray analysis displayed the presence of martensitic colonies as well as deposits of carbide precipitates in both weldments. The mechanical properties of these weldments, namely micro-hardness, tensile strength, and impact strength were also investigated. A comparative study has also been carried out for the same material using the conventional gas metal arc welding, in which the microstructure and mechanical behavior of regulated metal deposition weldments have been compared to those of gas metal arc weldments. Regulated metal deposition weldments showed better mechanical behavior than the gas metal arc weldments for low alloy steel.

Effect of ultrasonic impact treatment on microstructure and corrosion behavior of friction stir welding joints of 2219 aluminum alloy

Ultrasonic Impact Treatment (UIT) was performed to improve the corrosion resistance of 2219 aluminum alloy friction stir welding (FSW) joints. Results showed that the coarse grains on near surface of FSW joints were obviously modified and refined after UIT, and the thickness of the modified layer of different sub-regions was ranged from 90 to 120 μm. UIT increased intergranular corrosion resistance of 2219 aluminum alloy FSW joints in salt spray corrosion atmosphere. Free-corrosion potential of heat-affected zone (HAZ), which presented the worst corrosion resistance, was increased from −0.653 to −0.628 V, and the corrosion current density was decreased from 7.48 to 6.18 mA cm−2. The sensitivity index of stress corrosion cracking (SCC) of the joints was decreased from 0.139 to 0.129 in 3.5% NaCl solution after UIT, and the risk of crack initiation during SCC process was significantly inhibited. UIT improved the SCC resistance of 2219 aluminum alloy FSW joints by surface plasticity improvement, grain refinement and precipitates dissolution and redistribution.

Effects of different post-weld heat treatment conditions on mechanical properties and microstructure of welded joints

Post-weld heat treatment is a standard method to improve the performance of welded joints. Different heat treatment processes have different influences on the performance of welded joints. Therefore, it is of great significance to explore the impact of the heat treatment process on welded joints’ performance. This work applied three different heat treatment processes to the welded joints with three different properties. Then hardness test, impact test, tensile test, metallographic analysis and other means were used to evaluate the performance of welded joints after heat treatment. The following conclusions were drawn through the experiments: The change of phase compositions of the welded joints caused by the post-weld heat treatment was considered as the main reason for changes in mechanical properties of the welded joint. The difference in mechanical properties after different welding process and post-weld heat treatment combination was obtained, which has a guiding significance for practical production.