Laser Beam Welding Joints Research Articles

Microstructural evolution and fracture behaviour of dissimilar Al/Steel lap joints by laser beam oscillating welding

ABSTRACT The hybrid metal joining of aluminium alloy and steel has become the most intensively used candidate material for energy conservation and emission reduction in the automotive industry because of the comprehensive properties of low density, high strength and good corrosion resistance. In this work, experimental investigations were conducted on the laser beam oscillation welding of galvanised steel and aluminium alloy arranged in a lap configuration. Well-formed joints were successfully obtained with the aid of beam oscillating. Zigzag structures were observed at the interfacial area of Al–Fe joints instead of blocky structures due to the oscillation-driven effect of the beam. The stirring effect of the oscillating beam can promote the migration of the solute during the laser welding process, thus inhibiting the separation of components and decreasing the vulnerability to cracking. The interface zones of the laser-welded Al–Fe joints were principally made up of the Fe2Al5, FeAl, FeAl2, FeAl3 and Fe2Al5Zn0.4 phases. The joints welded with beam oscillation exhibited a tensile load and elongation amount of 1.07 kN and 0.775 mm, respectively, representing 115.67% of the loading capacity and 119.23% of the elongation compared to laser beam-welded joints without oscillation.

A comparative study of the galvanized DP980 steel and 2 GPa PHS welded joint via laser beam welding and cold metal transfer welding

Galvanized DP980 steel and Al-Si coated 2 GPa press-hardened steel (PHS) were joined via laser beam welding (LBW) and cold metal transfer (CMT) welding, respectively. The weld metal (WM) of LBW joints contains martensite, acicular ferrite, and bainite. The WM of the CMT joint consists entirely of acicular ferrite. The tensile strength of the LBW joint is 895 ± 5 MPa, slightly higher than that of the CMT joint by 50 MPa due to the presence of martensite. The total elongation is 4.1 ± 0.2 % and 5.0 ± 0.3 % for the LBW and CMT joints, respectively. The enhanced plasticity of the CMT joint was due to the soft WM plastic deformation, which increased the total deformation.

Porosity suppression and mechanical property improvement of wire-arc directed energy deposited TiCp/Al-Cu alloys joint by oscillating pulsed wave laser beam welding

Hybrid manufacturing technology combining wire-arc directed energy deposition (WA-DED) and laser beam welding (LBW) presents a promising avenue for efficiently manufacturing large-size aluminum alloy components. The high tendency of porosity defects, particle decomposition, and fusion zone softening are outstanding challenges in the LBW welding of additively manufactured particle-reinforced aluminum alloys. Herein, a WA-DED-processed Al-6.3Cu alloy embedded with 0.6 wt% TiC particles was employed as weldment. Four different laser beam modes, including continuous wave (CW), pulsed wave (PW), oscillating continuous wave (OCW), and oscillating pulsed wave (OPW), were used to join TiCp/Al-6.3Cu alloy. The effects of different laser modes on the porosity defects, microstructure evolution, and mechanical properties of WA-DED particle-containing aluminum alloy joints were studied comparatively. Multi-scale characterization results showed that the enhanced molten pool flow via laser beam modulation effectively suppressed porosity defects and facilitated the uniform particle distribution. The OPW mode provides an optimal effect on porosity inhibition and weld microstructure refinement compared to the pulsed or oscillating modulation modes. The heat-treated LBW joint via OPW mode achieved excellent comprehensive mechanical properties, whose elongation and ultimate tensile strength reached 9.5% and 449 MPa, respectively. This enhanced performance can be attributed to the decreased porosity, refined weld microstructure, and high-density nano-precipitation. This study provides fundamental guidance for the welding of high-strength Al-Cu alloy fabricated by additive manufacturing.

Modelling the Evolution of Phases during Laser Beam Welding of Stainless Steel with Low Transformation Temperature Combining Dilatometry Study and FEM

In this study, the evolution of volume fractions during laser beam welding (LBW) of stainless steel, with a specific focus on incorporating the low transformation temperature (LTT) effect using the dilatometer, has been proposed. The LTT effect refers to the phase transformations that occur at lower temperatures and lead to the formation of a martensitic microstructure, which will significantly influence the residual stresses and distortion of the welded joints. In this research, the LTT conditions are achieved by varying the Cr and Ni content in the weld seam by varying the weld parameter, including laser power, welding speed and filler wire speed. The dilatometer analysis technique is employed to simulate the thermal conditions encountered during LBW. By subjecting the stainless steel samples to controlled heating and cooling cycles, the kinetics of the volume fractions can be measured using the lever rule and empirical method (KOP and Lee). The phase transformation simulation model is computed by integrating the thermal and metallurgical effects to predict the volume fractions in LBW joints and has been validated using dilatometer results. This provides valuable insight into the relationship between welding parameters and phase transformations in stainless steel with the LTT effect during laser beam welding. Using this relationship, the weld quality can be improved by reducing the residual stresses and distortion.

Investigation of the microstructure and mechanical properties of Mg–Al–Zn alloy joints formed by different laser welding processes

Abstract The microstructure and mechanical properties of Mg–Al–Zn alloy joints by using autogenous laser beam welding (LBW) and laser-MIG hybrid welding, respectively, are investigated. The results show that the weld formation of the hybrid welding joint is relatively good, and there are mainly α-Mg matrix phases and β-Mg17Al12 strengthening phases in the weld metal. The microstructure in the fusion zone (FZ) of the two joints is different. The LBW joint is composed of columnar crystal and equiaxed dendrite. The hybrid welding joint consists of fine equiaxed grains, and the grain size in the laser zone is larger than that in the arc zone. The microhardness in FZ is higher due to the precipitation of the β-Mg17Al12 phase in this region. Under the optimized welding procedure, the strength coefficient of the two joints is >90%. There are many dimples on the tensile fracture surface of the hybrid welding joint, which is characterized by the pattern of the ductile fracture.

Improved strength and ductility on laser beam welded joints of 7085Al matrix nanocomposites by in-situ ZrB2 nanoparticles and Al3(Er, Zr) nanoprecipitates

Welding hot cracking, precipitates dissolution and coarsening during welding thermal cycle usually lead to the poor weldability of high-strength 7XXX series aluminum alloy. In this work, in-situ ZrB2 nanoparticles and Al3(Er, Zr) (L12) nanoprecipitates were used to synergistically optimize microstructure and enhance mechanical property of 7085Al nanocomposites laser beam welded joint (LBWJ). The results showed that ZrB2 and Al3(Er, Zr) could effectively modify dendritic morphology of fusion zone (FZ) and refine grains to 1.78 μm, which was beneficial to relieve welding hot cracking caused by coarse dendritic grains. Besides, ZrB2 ceramic particle and core-shell Al3(Er, Zr) with high thermal stability would significantly compensate the deficiency of η′ and η precipitates during welding thermal cycle. The joint efficiency (JE) of ZrB2/7085Al–Er LBWJ reached up to 73.4%. Its ultimate tensile strength (UTS) and elongation were enhanced to 415.3 MPa and 6.8%, increased by 25.4% and 23.6% as compared to the 7085Al LBWJ. Crack deflection and crack bridging induced by ZrB2 and Al3(Er, Zr) contributed to a ductile failure of ZrB2/7085Al–Er LBWJ. The synergetic effect of ZrB2 and Al3(Er, Zr) on nucleation and growth of Al grains in FZ was deeply revealed, and the strengthening and toughening mechanisms of ZrB2/7085Al–Er LBWJ were discussed in detail.

Improving the strength-ductility synergy and corrosion resistance of Inconel 718/316L dissimilar laser beam welding joint via post-weld heat treatment

Inconel 718/316L dissimilar welding is widely used in nuclear power plants, which suffers from the deterioration of mechanical properties and corrosion resistance after welding, attributed to the formation of brittle phase and the existence of residual stress. In this paper, the impact of post-weld heat treatment (PWHT) on Inconel 718/316L welding joints is systematically investigated. By conducting PWHT after welding, notable reductions in residual stress in as-welded joints are significantly reduced and the microstructure is improved, resulting in an enhanced strength-ductility synergy and corrosion resistance. The as-welded joints exhibit the generation of brittle Laves phase and welding residual stress in the fusion zone. After PWHT at 650 °C, a substantial increase in the quantity of fine-scale γ″ strengthening phases with a uniform dispersion distribution in weldment is observed, along with the release of residual stress. This combination yields an optimal strength-ductility synergy and corrosion resistance of the joint. However, the δ phase precipitates along in Laves phase boundary after PWHT at 850 °C, which exhibits a semi-coherent interface with γ matrix, and a non-coherent interface with the Laves phase, leading to severe stress concentration at the δ phase interface. This severe stress concentration could be a preferred location for crack initiation and propagation, resulting in a substantial loss in mechanical behavior. Additionally, the increase in the phase boundary of γ/γ″, γ/Laves, Laves/δ and γ/δ reduces the corrosion resistance of the joint. The findings of this study provide an effective strategy for improving the performance of Inconel 718/316L dissimilar laser beam welding joint.

Contrasting the mechanical and metallurgical properties of laser welded and gas tungsten arc welded S500MC steel

S500MC steel is a grade of high-strength low-alloy steel (HSLA) which is widely used in the automotive industry and for agricultural machinery and equipment. Considering properties of this alloy, selection of the welding process and parameters becomes essential to ensure that HSLA assemblies meet specific service requirements. In this work, mechanical and metallurgical properties of S500MC steel produced by autogenous laser beam welding (LBW) and automatic gas tungsten arc welding (GTAW) were compared. Tensile testing, metallography, hardness testing, and fractographic analysis were performed on the welded specimens, revealing that the heat input by these welding processes caused significant microstructural changes within the joints. In LBW samples, the heat input about 10 times lower than that in GTAW produced a finer microstructure, narrower fusion zone width, and smaller heat-affected zone. All fractures of the GTAW specimens occurred in the base metal, while all fractures of the LBW specimens occurred in the weld zone, both regardless of the heat input. GTAW joints exhibited higher mechanical properties (even higher than those obtained in the base metal) as compared to LBW joints.

Effect of niobium on the mechanical strength of the laser beam welding joints of molybdenum

The low strength and plasticity of molybdenum (Mo) fusion welding joints are the key problem hindering the application in the engineering structures field. The main reason for the low strength and plasticity of Mo joints is the low grain boundary bonding strength, which is also known as grain boundary brittleness. The segregation of oxygen (O) at the grain boundaries and the distribution of the lamellar MoO2 phases are the intrinsic reasons for brittleness. In this study, the Mo fusion welding joints were processed by laser beam welding. The maximum tensile strength of the unalloyed joint could only reach 169.8 MPa. Meanwhile, the maximum tensile strength of joints with Nb alloyed could reach 426.7 MPa. During the welding, the niobium (Nb) element preferred to reduce the O content and realize the second-phase strengthening at the grain boundaries. The results of XPS and TEM confirmed that Nb mainly existed in the form of Nb2O5 and NbC in the fusion zone (FZ) of joints with Nb alloyed. The SEM and EBSD showed that a certain amount of NbC is precipitated at the grain boundaries, and the amount of MoO2 is significantly reduced. The lamellar MoO2 could be clearly observed on the grain boundary surface of the FZ of the joints without alloying.

Microstructure and mechanical properties of laser beam welding joint of in-situ (ZrB2+Al2O3)/AA7N01 nanocomposites

In this paper, in-situ nanoparticles ZrB2 and Al2O3 are introduced to raise the mechanical properties of AA7N01 Laser beam welding (LBW) joint by in-situ melt reaction method. The effects of ZrB2 and Al2O3 nanoparticles on the microstructure and tensile properties of in-situ (ZrB2+Al2O3)/AA7N01 nanocomposites and LBW joints were studied. The experimental results indicate that ZrB2 nanoparticles provide more nucleation sites for grain nucleation and tend to aggregate at the grain boundary (GB). The average grain size of composites is greatly refined from about 110 μm to 20 μm. As the content of particles increased from 1 vol% to 3 vol%, the ultimate tensile strength (UTS) of nanocomposites is enhanced from 439.3 MPa to 538.2 MPa, the UTS of the LBW joint is increased from 246.7 MPa to 353.6 MPa. The effects of ZrB2 and Al2O3 nanoparticles on grain refinement and growth of matrix are analyzed. Furthermore, the strengthen mechanism induced by the precipitates and nanoparticles on the mechanical properties of composites and joints are also discussed.

A Comparative Study on Microstructural Characterization of Thick High Strength Low Alloy Steel Weld by Arc Welding and Laser Welding

Welding and the behavior of the weldments are important, since welding of high strength low alloy (HSLA) steels is a conventional method for manufacturing industrial parts. This work conducts a comparative investigation of microstructural characteristics and mechanical properties for joints of 16-mm-thick HSLA Q890 steel produced by multi-layer multi-pass shielded metal arc welding (SMAW) with filler wire and single-layer autogenous laser beam welding (LBW). The mechanical properties of the welded joints were assessed in terms of tensile and impact using butt joints. The results show that tensile failure occurred in the base metal during the tensile tests for most of the trials. The ultimate tensile strength and percent elongation of the LBW welded joint (973.5 MPa and 10%) are higher than those of the SMAW joint (951 MPa and 2.9%) due to the filler filling process of the SMAW process. The Charpy impact energy of the weld metal (16.4 J and 15.1 J) is lower than that of the heat-affected zone (18.5 J and 19.5 J) in the LBW joint and the SMAW joint.

Investigating the effect of residual stresses and distortion of laser welded joints for automobile chassis and optimizing weld parameters using random forest based grey wolf optimizer

The present investigation analyses the selection of the right welding method and joint and advanced testing methods (NDT) for highly durable automotive frames. Moreover, the present investigation analysis suggests the best machine learning (ML) algorithm for selecting the best weld method and optimal solution. The experiment was performed based on the response surface methodology (RSM) based design of the experimental approach. As a result, laser beam welding (LBM) and cross joint are the significant weld methods for automotive frames. The proposed ML algorithm successfully optimized the LBM input parameters as laser power = 1277 W, welding speed (WS) = 32.2 mm/s, focal point: 1 mm and working angle = 0.14 Rad with an average error of approximately 0.033. Based on the results, the optimum output weld parameters are bead width = 4322.7 µm, penetration depth (PD) = 3157.9 µm, total strain = 0.0098 mm/mm and residual stress = 645.2340 MPa, respectively.

Effect of Ti-Hf-Zr-Cu-Ni high entropy alloy addition on laser beam welded joint of Ti2AlNb based intermetallic alloy

• In this study, LBW of Ti-22Al-27Nb was experimented through addition of an interlayer of the filler, Ti-Hf-Zr-Cu-Ni HEA, into the joint and a comparison between the LBWJs of Ti-22Al-27Nb either prepared with or without addition of the filler was established through microstructural analysis by corelating its impact on mechanical properties at room temperature. Followings are the highlights of this experimental work. • The addition of Ti-Hf-Zr-Cu-Ni HEA into FZ of LBWJ of Ti-22Al-27Nb activated heterogenous nucleation due to difference of chemical composition between the BM and the filler, resultantly, fine grained B2 phase with greater fraction of HAGBs was evolved in the FZ. Grain refinement and higher misorientation angle between GBs in the FZ contributed an increase in hardness, tensile strength and percentage elongation of HEA adulterated LBWJ of Ti-22Al-27Nb. • The average hardness of the FZ (343.5 HV) and UTS (1062 MPa) of the HEA added LBWJ was found in close agreement with that of BM, 345 HV and 1060 MPa, respectively. • The percentage elongation of the joint, prepared with an interlayer of HEA, was measured up to 11.2%, which was 83.6% of the BM. • The LBWJ of Ti-22Al-27Nb, prepared with the addition of HEA, fractured from the junction of FZ and HAZ in a ductile mode while the LBWJ prepared without addition of Ti-Hf-Zr-Cu-Ni filler was ruptured from FZ in quasi-cleavage mode. Ti 2 AlNb based intermetallic alloys, a potential competitor for next-generation super alloys, are susceptible to high-temperature embrittlement due to nucleation of a metastable single B2 phase in the fusion zone (FZ) during laser beam welding (LBW). In this study, a high entropy alloy (HEA), Ti-Hf-Zr-Cu-Ni, was self-developed and introduced as an interlayer into laser beam welded joint (LBWJ) of Ti-22Al-27Nb to analyze its impact on the evolution of microstructure in the weld zone (WZ) and subsequently on joint performance. Microstructural examination was carried out through electron probe micro analysis (EPMA), electron backscattered diffraction (EBSD) analysis, high-resolution scanning transmission electron microscopy (HRSTEM) comprising bright field (BF), selective area electron diffraction (SAED) and high angle annular dark-field (HAADF) imaging. Addition of the HEA into FZ of LBWJ triggered heterogenous nucleation during solidification, resultantly, fine-grained B2 with a greater proportion of high angle grain boundaries (HAGBs) was developed. FZ of Ti-22Al-27Nb LBWJ, prepared with an interlayer of HEA, was composed of planar, cellular, columnar and equiaxed dendritic grains; a solidification mode which was different from that observed in LBWJ prepared without adulteration of the HEA. The impact of heterogenous nucleation during epitaxial solidification on mechanical properties was established through micro vickers hardness mapping and tensile test, conducted at room temperature. The average hardness, 343.5 HV, in the FZ of LBWJ prepared with an interlayer of HEA, was compatible with that of base material (BM), 345 HV. The ultimate tensile strength (UTS), 1062 MPa, and percentage elongation, 11.2%, of the HEA tempered LBWJ were found in close approximation with that of BM, 1060 MPa and 13.4%, respectively. A ductile mode of failure was observed during tensile test of the Ti-Hf-Zr-Cu-Ni supplemented LBWJ of Ti-22Al-27Nb, while quasi-cleavage mode of fracture was apparent in the joint of Ti-22Al-27Nb welded without addition of the HEA.

Experimental and numerical investigation of laser beam-welded Al–Cu–Li joints using micro-mechanical characteristics

The local tensile mechanical properties of laser beam-welded joints of AA2198 alloy with Al–Si filler wire were experimentally investigated. For this purpose, micro-flat tensile specimens were extracted from the fusion zone and the heat-affected zone. The chemical composition of the filler wire affects the local mechanical properties in the fusion zone, showing an approximately 26% decrease in yield strength from the radiation exposure side to the weld root side. The effect of post–weld heat treatment on the tensile mechanical behavior was additionally investigated for different heat treatment artificial ageing conditions. The maximum yield strength increase was noticed for 48 h of artificial ageing for the weld root side of the fusion zone. Several approximations were proposed to correlate the hardness measurements with the local tensile mechanical properties of the welded joint that allow for a fast assessment of the global tensile mechanical behaviour of the welded joint. To evaluate the effect of (i) artificial ageing and (ii) geometrical imperfections of the weld on the mechanical behavior of the welded joint, finite element analyses were performed, using the local mechanical properties as input to the model. It is shown that the local mechanical properties of the fusion zone play a pivotal role on the strain localization and fracture of the welded joint.

Effect of Ta microalloying on joint performance by tailoring the microstructure during laser beam welding of Ti-22Al-27Nb

The development of Ti2AlNb based alloys has set a strong competition between conventional Ni-based superalloys and titanium aluminides for aerospace industry due to their compatible/superior mechanical properties. With advent of time, progressive manufacturing technologies are being worked out to transform this novel alloy system into tangible engineering products. Laser beam welding (LBW) of Ti2AlNb based alloys is a provocative task due to evolution of metastable B2 phase in the fusion zone (FZ). In the present study, a comparative analysis on LBW of Ti-22Al-27Nb was carried out by preparing the joints with/without an interlayer of Tantalum (Ta) microfilm. The evolution of microstructure in the weld zone (WZ) was analyzed through Electron probe microanalysis (EPMA), Electron backscattered diffraction (EBSD) analysis, High-angle annular dark-field (HAADF), Bright field (BF) and Selected area electron diffraction (SAED) imaging. The effect of Ta on laser beam welded joint (LBWJ) of Ti-22Al-27Nb was established by correlating the room temperature mechanical properties (tensile properties and hardness) with the evolution of phases, grains and grain size distribution and inter/intra grain misorientations in the weld zone (WZ). The addition of Ta into FZ triggered heterogeneous nucleation, causing epitaxial as well as non-epitaxial mode of solidification in the weld pool. A substantial increase in tensile strength of Ta adulterated LBWJ of Ti-22Al-27Nb was the provenance of grain refinement and greater fraction of high angle grain boundaries (64.89%). The tensile strength and percentage elongation of LBWJ prepared with 0.01 mm thin interlayer of Ta was measured up to 1049 MPa (i.e. 99.15% of that of the base material) and 9.53% respectively. Further dilution of the LBWJ with Ta contributed no significant increase in tensile strength due to nucleation of Intermetallics along the periphery of FZ and caused an early failure.

Microstructures and properties of the dissimilar joint of pure molybdenum/T2 copper by single-mode laser welding

The fusion welding of molybdenum (Mo) and copper (Cu) is challenging task due to significant differences between chemical composition and physical properties of the two metals. A sound quality laser beam welding (LBW) joint between Mo and Cu is developed through the addition of pure Ni as an interlayer and laser beam offsetting. The evolution of microstructure in weld zone (WZ) and its impact on joint performance is analyzed through scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron backscattered diffraction (EBSD), tensile and hardness test. At room temperature, the LBW joint between Mo and Cu is ruptured from heat affect zone (HAZ) near fusion zone (FZ) under a tensile load of 209 MPa. The addition of Ni as interlayer between LBW joint of Mo and Cu contributed an increase of 37.79% in tensile strength and the joint is ruptured from HAZ beside the base material Cu. Such improvement in joint performance is attributed to grain refinement in FZ, coarsening of transition zone (TZ) between Mo and Cu and directional solidification towards Cu rich region in FZ due to addition of Ni into LBW joint between Mo and Cu. The research results provide reference for the welding between dissimilar materials with significantly different melting points.

Effect of various combinations of Ti and Zr interlayers on the tensile properties of laser welded joints of molybdenum

Molybdenum (Mo) is of great potential in the nuclear energy field, however, the embrittlement and the lower tensile strength limit the application of the fusion welded joints. Titanium (Ti) and zirconium (Zr) were synchronously added into the fusion zone (FZ) to improve the tensile strength and certain ductility of laser beam welding joints. By utilizing high-resolution scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and nanoindentation, the microstructures and mechanical properties of FZs in the joints under different alloying strategies with Ti and Zr were analyzed. Zr is mainly present in Mo as Mo2Zr, playing the second-phase strengthening effect; Ti is mainly present in Mo in an atomic state, playing a role of the solid - solution strengthening. The addition of Ti and Zr with different mass proportions can control the relative contents of Mo2Zr phase and solid - solution atoms in the FZ, control the distribution of zigzag and flat grain boundaries and influence the relative distributions of low - angle grain boundaries (LAGBs) and high - angle grain boundaries (HAGBs). In the end, combined addition of Ti and Zr is possible to improve the tensile strength while decrease the loss of ductility of the joint.

Feasibility study of FSW, LBW and TIG joining process to fabricate light combat aircraft structure

In this research, friction stir welding (FSW), laser beam welding (LBW) and tungsten inert gas (TIG) welding are used to join precipitation hardening aluminum alloy 2014-T6. This alloy is a potential candidate in heavy structural fabrication industries due to strength ratio. However, the joining of this alloy is a major problem in assembly line. Hence, to find an ideal method for welding this alloy, three processes were compared in terms of mechanical and metallurgical properties of welded joints. Results showed that the FSW joints disclosed better strength than other LBW and TIG joints. In comparison to LBW and TIG joints, FSW conceived narrow heat-affected zone and recorded maximum hardness of 135 VHN. Similarly, the maximum hardness in the LBW and TIG welded joints were 110 VHN and 92 VHN respectively. The reason for maximum strength in FSW joints is the finer size and uniform distribution of strengthening precipitate. (Particle size diameter of 39 nm, thickness of 29 nm).

Effect of filler wire and post weld heat treatment on the mechanical properties of laser beam-welded AA2198

The mechanical behavior of autogenously and non-autogenously laser beam-welded joints of Al-Cu-Li alloy AA2198 and the effect of post weld heat treatment are examined in this contribution. The deformation texture of the base material does not present any significant change in the macrotexture with applying different artificial ageing times. Autogenously and non-autogenously laser beam-welded joints present a decrease in yield stress and ultimate strength in the as-welded condition, approximately 45% and 36–38%, respectively, when compared with AA2198-Τ3 base material. The addition of the AA4047 filler wire increases the Si and Cu content in the grain interior and in the grain boundaries of the fusion zone of the welded joint. Micro-hardness measurements for autogenously laser-welded joints showed a decrease in hardness by 27% for the fusion zone and 42% for the heat-affected zone, when compared with the non-autogenously laser beam-welded joints. Α quality index was exploited to evaluate the tensile mechanical performance of the welded joints. It is observed that the non-autogenously welded joints always show a higher ‘quality’ than the respective autogenously welded joints and the highest quality index in terms of mechanical performance is achieved for the as-welded and the peak-aged conditions, respectively. Regardless of the post weld heat treatment condition, both autogenously and non-autogenously laser-welded specimens fractured in between the equiaxed and fusion zone during tensile loading.

A study on strengthening and toughening mechanism of laser beam welded joint prepared between Ti–22Al–27Nb and Ti–6Al–4V with an interlayer of Nb

In this study, laser beam welding (LBW) between Ti–22Al–27Nb and Ti–6Al–4V was experimented with and without an interlayer of Nb to analyze and compare the effect of Nb on evolution of microstructure in fusion zone (FZ) and its impact on weld joint performance at room as well as high temperature (650 °C). The nucleation and evolution of phases and crystals were examined through X-ray diffraction (XRD), electron probe microanalysis (EPMA), electron back scattered diffraction (EBSD), high resolution transmission electron microscopy (HRTEM) and high angle annular dark field (HAADF) imaging, respectively. The weld joint performance was evaluated through tensile and hardness tests. The adulteration of LBW joint between Ti–22Al–27Nb and Ti–6Al–4V through pure Nb contributed an increase of 28.70% in yield strength (YS), 10.22% in ultimate tensile strength (UTS) and 12.81% in percentage elongation. The evident reason for such an improvement in joint performance was attributed to the suppression of α′ martensite and nucleation of single phase B2 with fine grained structure, which provided greater fraction of high angle grain boundaries (HAGBs) in FZ. The LBW joint between Ti–22Al–27Nb and Ti–6Al–4V with an interlayer of Nb was ruptured from the base material (BM) Ti–22Al–27Nb during tensile straining at room temperature. All the LBW joints between Ti–22Al–27Nb and Ti–6Al–4V, either prepared with or without an interlayer of Nb, were fractured from the BM Ti–6Al–4V during tensile test at 650 °C.