Microstructure and tensile properties of laser beam welded Ti–22Al–27Nb alloys

Ti–22Al–27Nb alloys were welded using the laser beam welding process. The microstructure characterization and the tensile properties of the laser beam welded joints were investigated. The experimental results showed that a well-quality joint could be obtained using laser beam welding method. The fusion zone of the welded joint was composed of B2 phase. The tensile strength of the joints at room temperature was basically comparable to that of the base metal and the tensile ductility of the joints achieved 56% of the base metal. The average tensile strength of the welded joints at 650 °C was tested to be about 733 MPa, with the elongation of 2.93%.     

Effects of welding parameters and post-heat treatment on mechanical properties of friction stir welded AA2195-T8 Al-Li alloy

In this study, the effects of main welding parameters(rotation speed(ω) and welding speed(v)) on the microstructure, micro-hardness distribution and tensile properties of friction stir welded(FSW)2195-T8 Al-Li alloy were investigated. The effects of T6 post-treatments at different solution and aging conditions on the mechanical properties and microstructure characteristics of the FSW joints were also investigated. The results show that with increasing and v, both strength and elongation of the joints increase first, and then decrease with further increase of and v. All the joints under varied welding parameters show significant strength loss, and the strength reaches only 65% of the base metal. The effect of T6 post-heat treatment on the mechanical properties of the joints depends on the solution and aging conditions. Two heat treatment processes(480℃× 0.5 h quenching + 180℃× 12 h,520℃× 0.5 h quenching + 180℃× 12 h aging) are found to increase the joint strength. Furthermore,low temperature quenching(480℃) is more beneficial to the joint strength. The joint strength can reach 85% of the base metal. Whereas both low temperature aging(140℃× 56 h) and stepped aging(100℃× 12 h + 180℃× 3 h) processes decrease the joint strength. After heat treatment all the joints show decreased ductility due to the obvious grain coarsening in the nugget zone(NZ) and thermo-mechanically affected zone(TMAZ).     

Tensile properties of fiber laser welded joints of high strength low alloy and dual-phase steels at warm and low temperatures

High strength low alloy (HSLA) and dual-phase DP980 (UTS ⩾ 980 MPa) steels were joined using fiber laser welding in similar and dissimilar materials combinations. The welded joints were characterized with respect to microhardness and tensile properties at three different temperatures: −40 °C, 25 °C, and 180 °C. Tensile properties of the welded joints were compared to those of the base metal (BM) obtained under similar conditions. A good correlation was found between the welded joints and the BM in relation to the tensile properties obtained at the different temperatures. A general trend of increase in the yield strength (YS), the ultimate tensile strength (UTS) and energy absorption (EA) with decreasing temperature was observed; however, work hardening coefficient was not altered and insignificant scatter was observed in case of the elongation. However, in the DP980 steel, dynamic strain ageing was observed only in the BM.     

Experimental investigations on welding behaviour of sintered and forged Fe–0.3%C–3%Mo low alloy steel

Tungsten Inert Gas (TIG) welding is considered as one of the cleanest welding methods. It is generally adopted for thinner materials with moderate weld joint strengths. Welding of sintered porous materials continues to be a challenge due to the inherent porosity of the parent metals. The present research work attempts to address some of the issues relating to the welding behaviour of sintered and forged Fe–0.3%C–3%Mo low alloy steels under TIG welding. Rectangular strips of size 70 mm × 15 mm × 5 mm, obtained by blending, compacting and sintering of elemental powders of iron, graphite and molybdenum, were upset forged – both hot and cold in order to obtain alloy steel strips of various porosities. Two identical alloy steel strips of equal density were then welded both along longitudinal and transverse directions, by TIG welding, employing filler metal of suitable composition. The welded strips were then subjected to tensile test, hardness test, microstructural and Scanning Electron Microscope (SEM) fractography studies. Cold/hot upsetting of the sintered alloy preforms has led to enhanced density. As a result of improved density, their tensile strength and hardness values were also found to be enhanced. The welded alloy exhibited higher tensile strength compared to the un-welded base metal, due to strengthening by residual stress. Similarly, the strength and hardness of the welded alloy strips were found to be enhanced with increase in density. The tensile strength of welded joint is found to be higher compared to that of the base metal due to alloy metals segregation, rapid cooling and formation of acicular ferrite at the weldment of welded joint. No porosity was observed in the weld metal or Heat Affected Zone (HAZ) of the weld joint. However, the base metal had numerous micro pores, though pore migration towards weldment has not been observed.     

Optimised design of electrode morphology for novel dissimilar resistance spot welding of aluminium alloy and galvanised high strength steel

A novel resistance spot welding method of dissimilar materials of 6008-T66 aluminium alloy and H220YD galvanised high strength steel was presented, and the morphology of welding electrodes was designed optimally. Macrostructure, microstructure and mechanical property of the welded joints obtained with optimised electrodes were studied. Numerical simulation of current density distribution and temperature field during welding was also performed. The optimised electrodes were a planar circular tip electrode with tip diameter of 10 mm on the steel side and a spherical tip electrode with spherical diameter of 70 mm on the aluminium alloy side. The welded joint obtained with optimised electrodes could be regarded as a special welded-brazed joint, and an intermetallic compound layer composed of Fe₂Al₅ and Fe₄Al₁₃ with maximum thickness of about 4.0 μm was formed at the aluminium/steel interface in the welded joint. Tensile shear load up to 5.4 kN was achieved for the welded joint obtained with optimised electrodes. Current density distribution during welding with optimised electrodes was more homogeneous than that with F type electrodes. Furthermore, interfacial temperature in the welded joint during welding with optimised electrodes (about 915 °C) was lower than that with F type electrodes (about 985 °C).     

Research on fatigue behavior of electron beam welding joint of 06Cr19Ni10 austenitic stainless steel sheet

06Cr19Ni10 austenitic stainless steel sheet square butt joints without filler metal addition were fabricated using EBW (electron beam welding) processes. Fatigue properties, tensile properties and microstructure of the welded joints were studied. It was found that the yield strength, tensile strength, elongation and Vickers hardness of EBW joint can reach the level of base material performance. Fusion zones consist of coarse columnar dendritic grains, which are perpendicular to the weld pool boundary. The hardness of heat affected zone is lower than weld centreline. The reason is that the grain of heat affected zone under the action of electron beam heat source happened recovery and recrystallization. The present work suggests that S–N curve slope of welding joint should be revised to m = 10 under the condition of high stress levels, and S–N curve slope is still m = 3.0 under the condition of low stress levels. Fatigue cracks did not extend along the minimum thickness of the section. On the contrary, fatigue cracks extended along the maximum height of the section.     

Microstructure and tensile strength of friction stir welded joints between interstitial free steel and commercially pure aluminium

In the present study, the joining of interstitial free steel and commercial pure aluminium was carried out by friction stir welding (FSW) technique using tool rotational speeds of 600, 900, 1200 rpm and traverse speed of 100 mm/min. The microstructure and micro-hardness of the weld interface have been investigated. Optical microscopy was used to characterize the microstructures of different regions of friction stir welding joints. The scanning electron microscopy-back scattered electron (SEM-BSE) images show the existence of the different reaction layers in the welded zone. The Al₃Fe intermetallic compound has been observed in the weld interface and their thickness increase with the increase in tool rotational speed. Tensile strength was also evaluated and maximum tensile strength of ∼123.2 MPa along with ∼4.5% elongation at fracture of the joint have been obtained when processed at 600 rpm tool rotational speed.     

Tensile behavior of friction stir welded AA 6061-T4 aluminum alloy joints

In this investigation response surface methodology based on a central composite rotatable design with three parameters, five levels and 20 runs, was used to develop a mathematical model predicting the tensile properties of friction stir welded AA 6061-T4 aluminum alloy joints at 95% confidence level. The three welding parameters considered were tool rotational speed, welding speed and axial force. Analysis of variance was applied to validate the predicted model. Microstructural characterization and fractography of joints were examined using optical and scanning electron microscopes. Also, the effects of the welding parameters on tensile properties of friction stir welded joints were analyzed in detail. The results showed that the optimum parameters to get a maximum of tensile strength were 920 rev/min, 78 mm/min and 7.2 kN, where the maximum of tensile elongation was obtained at 1300 rev/min, 60 mm/min and 8 kN.     

Effect of groove design on mechanical and metallurgical properties of quenched and tempered low alloy abrasion resistant steel welded joints

Experimental investigations were carried out to study the influence of three different groove designs on mechanical and metallurgical properties of 15 mm thick Q & T (quenched and tempered) steel welded joints. Welding heat input variation corresponding to each joint configuration was kept to a minimal such that the objective of investigating, exclusively, the effect of varied weld volume on the mechanical and metallurgical performance of these joints could be accomplished. Mechanical performance of these joints was evaluated by subjecting them to transverse tensile testing, and Charpy V-notch impact testing of the weld zones at room temperature and 0 °C. The results of this study reveal that among all types of groove formations used for welding, double-V groove joint possessed maximum YS (yield strength) and UTS (ultimate tensile strength), besides maximum strength ratio (YS/UTS) that was followed by U-groove joint and C-groove joint, respectively. However, weld zone tested individually, for the cover as well as the root pass of the C-groove joint possessed highest CVN (Charpy V-notch) values, both at room temperature and 0 °C. Extensive microhardness studies of these weldments showed a wide variation in the microhardness values of the weld zone and the HAZ (heat affected zone). It was concluded that each groove formation/design exerted a significant influence on the heat dissipation characteristics of these joints, which is evident from different morphological features as revealed through optical microscopy. Scanning electron microscopic studies on tensile and impact tested specimens indicate that despite of achieving undermatched welds that were accompanied with a high degree of metallurgical heterogeneity, the mode of failure in the weld zone was largely ductile.     

Interfacial microstructure and mechanical property of resistance spot welded joint of high strength steel and aluminium alloy with 4047 AlSi12 interlayer

Dissimilar materials of H220YD galvanised high strength steel and 6008-T66 aluminium alloy were welded by means of median frequency direct current resistance spot welding with employment of 4047 AlSi12 interlayer. Effects of interlayer thickness on microstructure and mechanical property of the welded joints were studied. The welded joint with interlayer employed could be recognised as a brazed joint. The nugget diameter had a decreased tendency with increasing thickness of interlayer under optimised welding parameters. An intermetallic compound layer composed of Fe₂(Al,Si)₅ and Fe₄(Al,Si)₁₃ was formed at the interfacial zone in the welded joint, the thickness and morphology of which varying with the increase of interlayer thickness. Reaction diffusion at the steel/aluminium interface was inhibited by introduction of silicon atoms, which restricted growth of Fe₂(Al,Si)₅. Tensile shear load of welded joints experienced an increased tendency with increasing interlayer thickness from 100 to 300 μm, and the maximum tensile shear load of 6.2 kN was obtained with interlayer thickness of 300 μm, the fractured welded joint of which exhibiting a nugget pullout failure mode.     

Effect of welding parameters on microstructure and mechanical properties of AA6061-T6 butt welded joints by stationary shoulder friction stir welding

Stationary shoulder friction stir welding (SSFSW) butt welded joints were fabricated successfully for AA6061-T6 sheets with 5.0 mm thickness. The welding experiments were performed using 750–1500 rpm tool rotation speeds and 100–300 mm/min welding speeds. The effects of welding parameters on microstructure and mechanical properties for the obtained welds were discussed and analyzed in detail. It is verified that the defect-free SSFSW welds with fine and smooth surface were obtained for all the selected welding parameters, and the weld transverse sections are obviously different from that of conventional FSW joint. The SSFSW nugget zone (NZ) has “bowl-like” shapes with fairly narrow thermal mechanically affected zone (TMAZ) and heat affected zone (HAZ) and the microstructures of weld region are rather symmetrical and homogeneous. The 750–1500 rpm rotation speeds apparently increase the widths of NZ, TMAZ and HAZ, while the influences of 100–300 mm/min welding speeds on their widths are weak. The softening regions with the average hardness equivalent 60% of the base metal are produced on both advancing side and retreating side. The tensile properties of AA6061-T6 SSFSW joints are almost unaffected by the 750–1500 rpm rotation speeds for given 100 mm/min, while the changing of welding speed from 100–300 mm/min for given 1500 rpm obviously increased the tensile strength of the joint and the maximum value for welding parameter 1500 rpm and 300 mm/min reached 77.3% of the base metal strength. The tensile fracture sites always locate in HAZ either on the advancing side or retreating side of the joints.     

Feasibility study of friction spot welding of dissimilar single-lap joint between poly(methyl methacrylate) and poly(methyl methacrylate)-SiO2 nanocomposite

In this work, the feasibility of friction spot welding (FSpW) of a commercial poly(methyl methacrylate) (PMMA) GS grade and a PMMA 6 N/2 wt% silica (SiO₂) nanocomposite was investigated. Single-lap joints welded at rotational speeds of 1000, 2000 and 3000 rpm were produced. The analysis of the joint microstructure and material flow pattern indicated that joints could be produced using all of the tested welding conditions. However, the joint produced at 1000 rpm displayed sharp weld lines (weak links), indicating insufficient heat input, while the welds produced at 3000 rpm displayed excessive plastic deformation (bulging of the bottom plate), volumetric defects and a lack of material mixing in the welded area, associated with higher heat input. The weld produced at a rotational speed of 2000 rpm resulted in improved material mixing, which was indicated by the absence of weld lines and volumetric defects due to the more correct heat input. This welding condition was selected for further mechanical testing. Lap shear testing of PMMA GS/PMMA 6 N/2 wt% SiO₂ nanocomposite single lap joints welded at 2000 rpm resulted in an average ultimate lap shear strength of 3.9 ± 0.05 MPa. These weld strength values are equal to or better than those obtained using state-of-the-art welding techniques for PMMA materials, thereby demonstrating the potential of friction spot welding for thermoplastic nanocomposites.     

Effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded AA5083-H111 and AA6351-T6 aluminum alloys

The relatively new welding process friction stir welding (FSW) was applied in this research work to join 6 mm thick dissimilar aluminum alloys AA5083-H111 and AA6351-T6. The effect of tool rotational speed and pin profile on the microstructure and tensile strength of the joints were studied. Dissimilar joints were made using three different tool rotational speeds of 600 rpm, 950 rpm and 1300 rpm and five different tool pin profiles of straight square (SS), straight hexagon (SH), straight octagon (SO), tapered square (TS), and tapered octagon (TO). Three different regions namely unmixed region, mechanically mixed region and mixed flow region were observed in the weld zone. The tool rotational speed and pin profile considerably influenced the microstructure and tensile strength of the joints. The joint which was fabricated using tool rotational speed of 950 rpm and straight square pin profile yielded highest tensile strength of 273 MPa. The two process parameters affected the joint strength due to variations in material flow behavior, loss of cold work in the HAZ of AA5083 side, dissolution and over aging of precipitates of AA6351 side and formation of macroscopic defects in the weld zone.     

Microstructure evolution and mechanical properties of linear friction welded S31042 heat-resistant steel

S31042 heat-resistant steel was joined by linear friction welding(LFW) in this study. The microstructure and the mechanical properties of the LFWed joint were investigated by optical microscopy, scanning electronic microscopy, transmission electron microscopy, hardness test and tensile test. A defect-free joint was achieved by using LFW under reasonable welding parameters. The dynamic recrystallization of austenitic grains and the dispersed precipitation of NbCrN particles resulting from the high stress and high temperature in welding, would lead to a improvement of mechanical property of the welded joint.With increasing the distance from the weld zone to the parent metal, the austenitic grain size gradually increases from ~1μm to ~150μm, and the microhardness decreases from 301 HV to 225 HV. The tensile strength(about 731 MPa) of the welded joint is comparable to that of the S31042 in the solution-treated state.     

Investigation on microstructure and properties of dissimilar joint between SA553 and SUS304 made by laser welding with filler wire

The dissimilar joints between SA553 and SUS304 were produced by CO₂ laser welding with the ERNiMo-8 and ER308L filler wire. After welding parameters were optimized, qualified weld formations were made. Investigation on the microstructure showed that there were dual phases (martensite and austenite) in the ER308L weld, but only austenite in the ERNiMo-8 weld. For both joints, not only the microstructure gradient, but also the element gradient was observed near interfaces between weld metals and base metals. The Charpy impact and tensile test at room (25 °C) and low temperature (− 196 °C) was implemented. The cryogenic impact energy of the ER308L weldment was 51 J, lower than the value (84 J) of the ERNiMo-8 weldment. The corresponding cryogenic tensile strength of the two weldments was 1070 MPa and 960 MPa, respectively. The cryogenic tensile properties of both weldments were rather higher than requirements in the relevant standards. The ERNiMo-8 weldment showed relatively better comprehensive performance when the cryogenic toughness was considered.     

Comparative study on local and global mechanical properties of bobbin tool and conventional friction stir welded 7085-T7452 aluminum thick plate

7085-T7452 plates with a thickness of 12 mm were welded by conventional single side and bobbin tool friction stir welding (SS-FSW and BB-FSW, respectively) at different welding parameters. The temperature distribution, microstructure evolution and mechanical properties of joints along the thickness direction were investigated, and digital image correlation (DIC) was utilized to evaluate quantitatively the deformation of different zones during tensile tests. The results indicated that heat-affected zone (HAZ), the local softening region, was responsible for the early plastic deformation and also the fracture location for SS-FSW samples, while a rapid fracture was observed in weld nugget zone (WNZ) before yield behavior for all BB-FSW specimens. The ultimate tensile strength (UTS) of SS-FSW joints presented the highest value of 410 MPa, 82% of the base material, at a rotational speed of 300 rpm and welding speed of 60 mm/min, much higher than that of BB-FSW joints, with a joint efficiency of only 47%. This should be attributed to the Lazy S defect produced by a larger extent of heat input during the BB-FSW process. The whole joint exhibited a much higher elongation than the slices. Scanning electron microscopic (SEM) analysis of the fracture morphologies showed that joints failed through ductile fracture for SS-FSW and brittle fracture for BB-FSW.     

Research on fatigue behavior of welded joint spraying fused by low transformation temperature alloy powder

Modification of spraying fused (MSF) of plasma arc as heat source was used to improve the fatigue performance of welded joint, which both fundamentally reduced stress concentration at weld toe and achieved metallurgical bond between spraying fused coating and welding. The low transformation temperature alloy powder was applied to the method of MSF. After spraying fusion, especially spraying fused joint by low transformation temperature alloy powder, the distribution of residual stress is more difficult to be obtained. Finite element (FE) simulation as an important tool was used to determine the stress field and temperature field of spraying fused joint. Simulated results show that as-welded joint and welded joint spraying fused by conventional nickel base alloy powder (Conventional-joint) present tensile stress. The stress of welded joint spraying fused by low transformation temperature alloy powder (LTT-joint) is compressive stress. Fatigue test results indicated that under the condition of 2 × 10⁶ cycles, the fatigue strength of as-welded joint is 135 MPa, while that of Conventional-joint and LTT-joint is 218 MPa and 235 MPa, respectively. The fatigue strength of Conventional-joint increases by 61.48%, and fatigue strength of LTT-joint increases by 74.07%.     

Effect of post weld heat treatment on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel weldments

The effect of postweld heat treatment (PWHT) on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel joints with ER316LMn filler material was investigated. PWHT aging was performed for 1 h at four different temperatures of 600 °C, 760 °C, 870 °C and 920 °C, respectively. The microstructure revealed the sigma phase precipitation occurred in the weld metals heat-treated at the temperature of 870 °C and 920 °C. The PWHT temperatures have the less effect on the tensile strength, and the maximum tensile strength of the joints is about 630 MPa, reaching the 95% of the base metal, whereas the elongation is enhanced with the rise of PWHT temperatures. Meanwhile, the sigma phase precipitation in the weld metals reduces the impact toughness.     

Defect features and mechanical properties of friction stir lap welded dissimilar AA2024–AA7075 aluminum alloy sheets

5 mm-Thick dissimilar AA2024-T3 and AA7075-T6 aluminum alloy sheets were friction stir lap welded in two joint combinations, i.e., (top) 2024/7075 (bottom) and 7075/2024. The influences of process conditions (welding speed and joint combination) on defects (hook and voids) features and mechanical properties of joints were investigated in detail. It was found that the hook deflects largely upwards into the stir zone (SZ) at lower welding speeds (50, 150 mm/min) in both combinations. The process conditions significantly affect the hook geometry which in return affects the lap shear strength. In all 2024/7075 joints, voids appear and the joints fracture from the tip of hook on AS along the SZ/TMAZ (thermomechanically affected zone) interface in lap shear test (tensile fracture mode). In 7075/2024 joints, the hook on RS horizontally extends a large distance into the bottom stir zone at higher welding speeds (225, 300 mm/min). The joints fracture in three modes: shear fracture along the lap interfaces, tensile fracture and the mix fracture of both. In both joint combinations, the lap shear strength generally increases with the increase of welding speed. 7075/2024 Joints show higher failure load than 2024/7075 joints at lower welding speeds while the opposite result appears at higher welding speeds.     

Formation and mechanical properties of stationary shoulder friction stir welded 6005A-T6 aluminum alloy

6005A-T6 aluminum alloy is welded by stationary shoulder friction stir welding (SSFSW). At a constant rotational velocity of 2000 rpm, the effect of welding speed on mechanical properties of SSFSW joint are investigated in detail. Defect-free joint with gloss surface and small flash is attained and no cracks appear at the bending angle of 180°. Compared with traditional friction stir welding (FSW), width of rotational shoulder affected zone is relatively small because of the smaller diameter of rotational shoulder. Increasing welding speed is benefit for reducing the width of softening region and the softening degree. The fracture position of welding joint locates in thermo-mechanically affected zone and the fracture surface morphology presents the typical ductile fracture. The maximum tensile strength of joint at the welding speed of 400 mm/min reaches 82% of base metal (BM).