Tensile Properties Of Welded Joints Research Articles

Microstructures and properties of 7075 aluminum alloy and CP780 steel resistance spot welded joint assisted by magnetic field

Joining steel and aluminum is vital for lightweight automobile but still challenging due to their different physical properties. Herein, resistance spot welding tests were performed on CP780 high-strength steel (thickness 1 mm) and 7075 aluminum alloy (thickness 1.5 mm) dissimilar metals under steady-state magnetic field. The influences of magnetic field (B = 40 mT) on the structure of welded joints, the phase composition/content of intermetallic compounds, and tensile properties of welded joints were analyzed under different welding current conditions (I = 9 kA,10 kA, 11 kA, and 12 kA). At the same welding current, the Lorentz force generated by the additional magnetic field promoted the outward circumferential movement of the molten metal in the weld along the horizontal surface , as well as increased the diameter of the Fe/Al contact interface in the weld nugget along the horizontal direction, conducive to the effective utilization of heat of the resistance spot welding. Except under (11 kA-0 mT) and (11 kA-40 mT), welded joints under other welding parameters displayed a few welding defects, such as incomplete fusion and shrinkage cavity formed at the cross-section of the welded joints. Therefore, the synergism between the magnetic field and appropriate welding current held important roles in the formation of welded joints without obvious welding defects. The intermetallic compounds of all the welds were mainly composed of (Fe, Si)Al2 and (Fe, Si)Al5. Meanwhile, the thickness and content of the intermetallic compounds layer reduced under a magnetic field at the same welding current, significantly improving the tensile properties of the welded joints. The comprehensive properties of welded joints were the best under 11 kA-40 mT, with an average shear force increase from 3.02 kN to 3.49 kN (15.56%) and an average displacement increase from 1.01 mm to 1.22 mm (20.79%). Overall, the proposed dissimilar aluminum/steel resistance spot welded joint assisted by magnetic field looks promising for lightweight automobile use.

Tensile properties of welded joints with delayed hydride crack

In this work, a procedure for producing tensile coupon specimens with naturally delayed hydride cracks was proposed, and the tensile properties of the specimens were studied. Firstly, a delayed hydride crack was prefabricated on the welded plate according to the relevant specification, and the crack type was determined by microstructure and macrostructure observation and analysis. Secondly, the tensile coupon specimens of welded joints with or without delayed hydride cracks were cut from the welded plate. Finally, tensile tests of welded joints were carried out, and the strain and displacement were monitored by a digital image correlation system. The test phenomena, fracture mode and the tensile properties of the welded joint were analysed according to the stress-strain curve, the strain cloud map and the tensile property parameters. When the specimen fractured at the base metal, the effect of delayed hydride crack on the strength and deformation of the welded joints was insignificant. The cracked area ratio was relatively small (e.g. 1.91% to 22.5%). When the specimen fractured at the cracked region, the cracked area ratio was relatively large (e.g. 16.77% to 39.62%). The fracture modes could be divided into two types: the full-sectional yield fracture and the low stress fracture. The remaining ultimate strength, yield-to-tensile ratio and elongation of low stress fracture specimens showed a linear decline with the increase of cracked area ratio. For specimens with cracked area ratio between 16.77% and 22.5%, the differences in fracture locations might be caused by the pattern and angles of the crack.

High-temperature mechanical properties and microstructure of welded joint in GH4169/IC10 dissimilar nickel-based superalloys by vacuum electron beam welding

Jointing precipitation-reinforced GH4169 and newly-developed IC10 nickel-based superalloy through vacuum electron beam welding (VEBW) has become increasingly attractive for aeroengine's blade and disc. In this study, solution treatments (GH4169 for 980 °C/1.5 h and IC10 for 1180 °C/2 h) was chosen before welding, and different aging treatments (900 °C, 950 °C, 1000 °C, 1050 °C and 1100 °C for 6 h, respectively) were used for eliminating uneven compositions and structures of the GH4169/IC10 welded joint after VEBW method. Through optical microscopy (OM) observations, there are distinct morphological differences between the base metal (BM) and fusion zone (FZ) regions, with the BMs regions mainly being equiaxed and the FZ region mainly being dendritic grains after VEBW. Through scanning electron microscopy (SEM) observations, the carbides are mainly distributed at grain boundaries in BMs, and Ni–Cr–Nb phases are the dominant second phases in the FZs after VEBW. Moreover, the grain orientation is obviously strong in FZs with adjacent {001} orientation by electron backscattered diffraction (EBSD) characterizations. while grain orientation chiefly of BMs presents anisotropy. After heat treatments, the maximum microhardness of the welded joint was obtained after aging at 900 °C (242–258 HV), and the minimum microhardness was obtained after aging at 1050 °C (183–190 HV). Besides, among the aged welded joints, the 900 °C aged welded joint has the best high-temperature mechanical properties (tensile strength for 559 MPa and elongation for 19.3%) through high-temperature tensile tests, owing to the strengthening effect of numerous γ′ and γ′′ precipitates, nevertheless, 1050 °C aged welded joint has lower tensile strength than solution treated welded joint, mainly resulting from the numbers of δ precipitates isolating matrix. Moreover, combined with transmission electron microscopy (TEM) observations, the carbides, γ′, γ′′, and δ precipitates lead to different high-temperature tensile properties of welded joints, the transformation of γ′′ precipitates and coarsening of γ′ precipitate promote fracture crack initiation and propagation along grain boundaries.

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.

Studies on microstructure and properties of TiB2–Al3Ti ceramic particles reinforced spray-formed 7055 aluminum alloy fusion welded joints

Due to the brittle weld joints and worsening hot cracking tendency of spray-formed (SF) 7055 aluminum alloy, they are regarded as un-weldable. In this study, TiB2–Al3Ti/7055 (MA) aluminum matrix composites manufactured by the master alloy method were used to connect SF 7055 aluminum alloy. In the as-weld state, ceramic particles refine α-Al grains in weld metal (WM) and reduce the hot cracking tendency of weld joints. The tensile properties of weld joints increased from 240 ± 5 MPa, 1.4 ± 0.24% (7055) to 284 ± 5 MPa, 4.0 ± 0.35% (MA). In the heat treatment states (T6, T76, and RRA), the mechanical properties and corrosion resistance of MA-WM are superior to 7055-WM. The tensile strength of MA-T6 (485 ± 20 MPa, 3.10 ± 0.23%) is the best of the three heat treatment states, while the corrosion resistance of MA-T76 is the best. MA-RRA gains mechanical properties similar to MA-T6 and corrosion resistance close to MA-T76.

The Influence of Tool Shape on Plastic Metal Flow, Microstructure and Properties of Friction Stir Welded 2024 Aluminum Alloy Joints

In this paper, the effect of different shapes of tool pin on the plastic flow of 2024-T6 aluminum alloy during friction stir welding was studied. In order to observe the plastic flow of materials more clearly, we chose the method of friction stir welding of dissimilar materials, considering the different corrosive characteristics of aluminum alloys made of different materials when exposed to the same corrosive liquid. By studying and comparing the temperature field, macro and microstructure, microhardness and tensile properties of welded joints, the results indicated that the metal in the weld nugget zone (WNZ) mainly came from the base metal of the advancing side, the thread being the driving force of the downward movement of the FSW plastic metal. The deep groove thread tool pin had the strongest ability to drive the metal downward. The conical cam thread tool pin had the strongest stirring effect on materials and the best metal fluidity. The macroscopic morphology, microstructure, mechanical properties and fracture morphology of different joints were analyzed, and the results showed that all joints could form an excellent union, with an onion ring pattern appearing in cross-section. The minimum grain size of the WNZ formed by the conical cam thread stirring head was 7~12 μm; the hardness was least at the junction of the heat affected zone (HAZ) and the thermo-mechanically affected zone (TMAZ). However, the hardness of the weld formed by the conical cam thread at this point was higher than that of other stirring heads; the tensile strength of all joints was more than 80% of the BM, and the maximum tensile strength of the joint welded by the conical cam thread tool pin was 364.27 MPa, accounting for 86.73% of the base metal (BM). The elongation after break was 14.95%. Tensile fracture morphology analysis showed that all joints were fractured by plastic fracture.

Characterization of friction stir welded AA 3003-H24 aluminum alloy plates

AA 3003-H24 aluminum alloy plates were butt-welded in order to investigate the effect of friction stir welding process variables on the structural properties of the welded joints. The welded joints were characterized using macro-structural investigations; and tunnel-type defects with varied sizes were detected to occur. At a welding speed of 50 mm/min, tunnel-type defects with large size were found to occur in joints welded with the tool rotational speed of 500 and 1000 rpm. The tunnel-type defects were detected to occur in welded joints produced with the process parameters of 80 mm/min welding speed and 500 and 800 rpm tool rotational speed. However, cavity-type defects were observed to occur at both welding speeds. Even, defects were found to occur in the welded joints, all welded joints were detected to fracture between the base metal and the heat-affected zone, except for the joints welded under the process parameters of 50 mm/min welding speed, 500 and 1000 rpm tool rotational speed. The highest ultimate tensile strength among all the welded joints was measured to be 128 MPa produced under the process parameters of 50 mm/min welding speed and 800 rpm tool rotational speed. It has been revealed that there is a good correlation between the size of the defects and the tensile properties of welded joints. An examination on the fracture surface of the welded joints revealed that welded joints were fractured in ductile manner except the joint produced under the process parameters of 50 mm/min welding speed and 500 rpm tool rotational speed.

Tensile Behaviour of Friction Stir Welded Joints of Different Aluminium Alloys

This paper investigates the outcome of base metals and their temper condition on tensile and fracture behavior of friction stir welds of various work and precipitation hardening aluminium alloys in different tempers (AA1100-O, 5052-H, AA5086-O & H25, AA2024-O & T6, and AA6061-T651). The type and temper of aluminium alloys affected the tensile, and fracture behavior of weld joints. The extent of improvement in tensile properties of welded joints increased with a decrease in hardness (i.e., from T6 or H to O) of base metals. Softening was not observed for welded joints when base metal was in an annealed temper and an opposite trend was observed for hardened tempers ‘H’ and ‘T6’. Fracture location moved towards the weld centre with the change in temper from ‘O’ to ‘H’ and ‘T6’, hardness minima were closer to base metal hardness in the first case than later. The mode of fracture was ductile for all the weld joints except AA2024-T6 and AA 6061-T651. Except for AA2024-T6 and AA 6061-T651, all weld joints had ductile fracture mode.

Investigating the effect of process parameters on weld pool thermal history and mechanical properties of laser welded Inconel 625 and Duplex stainless steel 2205 dissimilar welds

In present study, welding of Inconel 625 and 2205 grade duplex stainless steel (DSS 2205) was carried out using a 2 kW Yb-fiber laser. An infrared (IR) pyrometer was used to log the thermal history of the weld pool. The molten weld-pool lifetime and cooling rates were accessed through the recorded data, and their effect on microstructure, elemental segregation, hardness and tensile properties of welded joints was investigated. The weld bead was composed of columnar and equiaxed dendritic grains. The microstructure exhibited refinement with increase in cooling rate, reducing the micro-segregation of Molybdenum (Mo) and Niobium (Nb) in the inter-dendritic spacing which was further investigated through XRD analysis. Also, tensile strength was found to be maximum i.e., 896.4 ± 8.1 MPa in the samples welded at 1950 W, 5500 mm/min which exhibited the fastest cooling within the range of parameters selected.

Investigation on microstructure and properties of dissimilar joint between TRIP800 and QP980 fabricated by laser welding

Dissimilar weld joints of QP980 and TRIP800 were fabricated by a fibre laser. The microstructure and mechanical properties of dissimilar weld joints were studied. The tensile properties of weld joints were not influenced by the narrow softening zone with a less reduction in hardness of ∼25 HV from the QP980, which contributed to fracture in TRIP800. The DIC images showed that the location of maximum strain was changed from the QP980 side to TRIP800 side during the tensile test of QP980 (1.2 mm)–TRIP800 (1.4 mm) joints. The dissimilar weld joints were characterised by the limited dome height test (LDH). The LDH values were varied with the punch pole location, as a result of the softening zone and non-uniform microstructure on the heat-affected zone of joints.

Microstructural characteristics and tensile properties of gas tungsten constricted arc (GTCA) welded Inconel 718 superalloy sheets for aeroengine components

Abstract Inconel 718 is a nickel-based superalloy, typically used in high temperature aerospace applications due to its exceptional mechanical properties and weldability. However, it is susceptible to solute segregation and coarser interconnected laves phase evolution in weld metal due to the high heat input in the gas tungsten arc welding (GTAW) process which drastically reduces the tensile properties of welded joints. It is also susceptible to HAZ microfissuring and liquation cracking issues owing to the evolution of low melting temperature eutectic film at the grain boundaries. To overcome this problem, a newly emerged novel gas tungsten constricted arc welding (GTCAW) process, principally differentiated by magnetic arc constriction and high frequency accentuation of the arc, is used to join Inconel 718 superalloy. The primary objective of this investigation is to evaluate the microstructural characteristics and tensile properties of GTCA welded Inconel 718 superalloy sheets (2 mm thick), fabricated using optimized process parameters, and compare its performance with the base metal. Results showed that GTCA welded joints exhibited 99.20 % and 73.5 % of base metal strength and ductility claiming significant advantages over the GTAW process. It is correlated to the grain refinement in the fusion zone and the evolution of finer discrete laves phase in interdendritic areas of the weld. The basic mechanism responsible for fusion zone grain refinement and corresponding influence on tensile properties of joints is also discussed in brief with regard to the mechanics of arc constriction and pulsing.

Microstructural characteristics and tensile properties of gas tungsten constricted arc (GTCA) welded Inconel 718 superalloy sheets for aeroengine components

Abstract Inconel 718 is a nickel-based superalloy, typically used in high temperature aerospace applications due to its exceptional mechanical properties and weldability. However, it is susceptible to solute segregation and coarser interconnected laves phase evolution in weld metal due to the high heat input in the gas tungsten arc welding (GTAW) process which drastically reduces the tensile properties of welded joints. It is also susceptible to HAZ microfissuring and liquation cracking issues owing to the evolution of low melting temperature eutectic film at the grain boundaries. To overcome this problem, a newly emerged novel gas tungsten constricted arc welding (GTCAW) process, principally differentiated by magnetic arc constriction and high frequency accentuation of the arc, is used to join Inconel 718 superalloy. The primary objective of this investigation is to evaluate the microstructural characteristics and tensile properties of GTCA welded Inconel 718 superalloy sheets (2 mm thick), fabricated using optimized process parameters, and compare its performance with the base metal. Results showed that GTCA welded joints exhibited 99.20 % and 73.5 % of base metal strength and ductility claiming significant advantages over the GTAW process. It is correlated to the grain refinement in the fusion zone and the evolution of finer discrete laves phase in interdendritic areas of the weld. The basic mechanism responsible for fusion zone grain refinement and corresponding influence on tensile properties of joints is also discussed in brief with regard to the mechanics of arc constriction and pulsing.

Effect of Welding Speed and Post Quenching on the Microstructure and Mechanical Properties of Laser-Welded B1500HS Joints

In this research, B1500HS high-strength steel with different thicknesses were laser welded, and the effects of welding speed and post quenching were investigated by analyzing the microstructure, microhardness distribution, and high-temperature tensile properties of weld joints. The results show that an obvious difference can be found in the metallographic structure and grain morphology of the weld joint at different locations, which also lead to the significant uneven distribution of hardness. After quenching, the grain size of the original heat-affected zone was uniform, the columnar grains in the fusion zone were transformed into fine equiaxed grains, and no obvious hardness difference can be found in the weld joint. For the weld joint without quenching, the increase of welding speed can reduce the dimensions of grains of fusion zone and coarse grain zone, and slightly increase the hardness of these regions. In contrast, welding speed change has little influence on the microstructure and hardness of the weld joint after quenching. The high-temperature flow stress–strain curves of fusion zone welded under different welding speeds were calculated based on the mixture rule. The analysis results indicated that the fusion zone has higher strength but lower elongation than the base metal. In addition, the change of welding speed has a small impact on the high-temperature tensile properties of the fusion zone.

Effect of Weld Zone Shape on Microstructure and Tensile Properties in Friction Stir Welding Process

This article presents the effect of weld zone shapes on microstructure and tensile properties of weld joints in friction stir welding. Experiments are conducted using four different tool pin profiles that are cylindrical, conical, cylindrical-conical and stepped-conical for analysing the weld zone shape. The weld zone shape properties are defined by characteristic length. Grain size and mode of fracture surface behavior are analysed by optical microscope and scanning microscope respectively and tensile strength is measured by universal testing machine. It is also observed that the weld zone shape of all pin profile tool is vase shape. In which, cylindrical, conical and cylindrical-conical pin profile tools produce basin dominant vase shape and stepped-conical pin profile tool produces cylinder dominant vase shape. The experimental result shows that the weld joint fabricated by stepped-conical pin profile tool produces the smallest grain, good ductile fracture mode and highest tensile properties as compared to other pin profile tool. This analysis shows that cylinder dominant vase shape produces high tensile properties and enhance ductile fracture mode in the weld joint.

Microstructure and ratcheting behavior of 6061 aluminum alloy laser-MIG hybrid welding joint

In this paper, 6061-T6 aluminum alloy was welded by laser-MIG hybrid welding. The microstructures of the upper part of the weld center, the lower part and the edge of the weld near the fusion line in the welded joint were analyzed. The hardness and mechanical properties of welded joints were analyzed in detail. The ratchet strain of 6061 aluminum alloy welded joints was tested, and the asymmetric stress control method was used to test the ratchet strain of 6061 aluminum alloy welded joints. The results show that ratcheting strain increases with the increase of average stress and stress amplitude, and has the characteristics of cyclic softening first and then hardening. The degree of hardening increases with the increase of the maximum cyclic stress. Cyclic hardening is mainly caused by the uninterrupted dislocations in the process of cycling. The accumulation of ratchet strain results in plastic damage of materials. Pre-ratcheting can improve the tensile properties of welded joints by 6.49% and 97.7% yield strength, which is mainly attributed to cyclic hardening caused by ratcheting strain.

Autogenous Tungsten Inert Gas and Gas Tungsten Arc With Filler Welding of Dissimilar P91 and P92 Steels

Creep strength ferritic/martensitic modified 9Cr-1Mo-V-Nb (P91) steel also designated as ASTM A335 and P92 steel are used for piping, cladding, ducts, wrappers, and the pressure vessel in Gen IV nuclear reactors. In the present investigation, a comparative study of the effect of autogenous tungsten inert gas welding (A-TIG) with double pass and multipass gas tungsten arc (GTA) welding with filler on microstructure evolution in the weld fusion zone and the mechanical properties of P91 and P92 steel welded joints was carried out. The microstructure evolution was studied in as-welded and postweld heat treatment (PWHT) condition. The study also focused on the evolution of δ-ferrite patches and their influence on the tensile properties of welded joints. PWHT was carried out at 760 °C with durations from 2 to 6 h. To study the effect of δ-ferrite evolution on mechanical properties, Charpy toughness, microhardness, and tensile tests were performed. The acceptable microstructure and mechanical properties were obtained after the 6 h of PWHT for A-TIG arc welding process while for GTA weld with filler wire, it was obtained after the 2 h of PWHT at 760 °C.

Improving formability of laser welded automotive dual phase steels with local cooling

A new laser welding process with the local cooling was presented and applied to two automotive dual phase steels, DP780 and DP980. The microstructure, microhardness, tensile properties of welded joints and limiting dome height (LDH) of welded blanks were investigated. It is observed that the local cooling during laser welding process can greatly reduce the martensite tempering and thus reduce the heat affected zone softening. The laser welded joints with the local cooling all failed at the base metal, and exhibit the comparable strength and ductility with the base metal. For the welded blanks with the local cooling, LDH is increased significantly, and failure initiates from the weld and propagates perpendicular to the weld.

Microstructure and Softening of Laser-Welded 960 MPa Grade High Strength Steel Joints

The microstructural evolution of laser-welded 960 MPa grade high strength steel joints and its effect on softening behavior of heat affected zone (HAZ) were investigated in this paper. The results show that microstructure of HAZ and fusion zone (FZ) is composed of lath martensite and bainitic ferrite. The microstructure of mixed grained zone presents strip-like characteristics and small block martensite distributes along the grain boundary. The grain size near the fusion line is about 25 lm, and the grain size in the fine grain zone is less than 5 lm. Microhardness of HAZ and FZ is lower than base metal. The soft zone locates in transitional region between tempering zone and mixed grained zone due to the interaction of the martensite tempering and the recovery and recrystallization of the rolled microstructure. Microhardness of soft zone is 310 HV and drops 18% compared to base material. Welding heat input has a remarkable effect on the width of soft zone and microhardness. The tensile properties of weld joints are closely related to the softening behavior of HAZ.

Microstructure and Properties of Friction Stir Welded Joints of Al-Mg-Sc Alloy Plates

Abstract The hot rolled and cold rolled-annealed plates of Al-Mg-Sc alloys were welded by friction stir welding. The hardness distribution and the tensile properties of welded joints were measured; the relationships between the microstructure and the properties of the welded joints were studied by means of optical microscopy and transmission electron microscopy. The results show that the welding coefficients of two plates are as high as 92%, the hardness and strength of their weld nugget zones are the lowest, and the fracture of their welded joints happens at weld nugget zones during tensile testing. The decrease of the substructure strengthening caused by the partial recrystallization and the loss of precipitation strengthening from Al3(Sc, Zr) particles result in the decline of hardness and strength of Al-Mg-Sc alloy welded joints.

Tensile Properties of Weld Joints of Aluminum Alloy Casting and Rolled Plates

Tensile Properties of Weld Joints of Aluminum Alloy Casting and Rolled Plates