Properties Of Laser Welds Research Articles

Influence of adjustable ring modes on molten pool behavior and microstructure of Al–Si coated boron steel in fiber laser welding

The influence of adjustable ring modes on the phase transition and microstructural evolution in conduction mode laser welding of Al–Si coated boron steel was investigated. Distinct geometric variations and molten pool behavior were observed through a ring-shaped beam effect. The ring beam introduced by ring-beam-mode (RBM) and dual-beam-mode (DBM) laser welding inhibited Al segregation into the fusion zone (FZ). The ring beam caused the Al molten particles to be driven towards the outer boundaries of the weld pool. A ring-beam-mode (RBM) and a dual-beam-mode (DBM) laser welding inhibited Al segregation into the FZ, resulting from a minimal temperature gradient and extension of the solidification time. Phase transition calculations demonstrated that a mount of residual ferrite within the FZ is significantly correlated with the Al concentration at specific temperature points, indicating a predominant role of a central-beam-mode (CBM) FZ in δ-ferrite formation. The RBM and DBM effectively suppressed Al segregation into the FZ, leading to a reduction in ferrite formation and the development of a refined microstructure characterized by a uniform and high density of geometrically necessary dislocations. Electron backscattered diffraction (EBSD) analysis revealed a higher proportion of low-angle grain boundaries in the RBM and DBM, attributed to the unique thermal distribution induced by the ring beam. These findings highlight the critical role of beam mode in tailoring the microstructure and properties of laser welds in Al–Si coated boron steel.

Microstructure and properties of laser welding Ni-based alloy/austenitic stainless steel with filler wire for nuclear reactor pump can end sealing

The current study investigates the microstructure and properties of laser welding involving Hastelloy C-276 and 304 stainless steel with filler wire, which is closely related to nuclear reactor pump can end sealing. The experimental results indicate the presence of an unmixed zone (UZ) and a small amount of Mo-rich secondary phase in weld seam, and microstructure of UZ is composed of austenite and ferrite phases. Laser welding enhances the ratio of low-angle misorientation and the uniformity of elements macro-distribution. The end sealing property of nuclear reactor pump can is characterized by anti-peel property of weld joints. The welded joint has local fracture and through fracture in the test of anti-peel property. The weld with local fracture exhibits superior anti-peel property. The joint crack starts at the bottom of the UZ. The anti-peel property of the welded joint is 239.6 ± 4.7 N/mm and mainly related to the weld penetration. The corrosion property of welded joints is determined by the elements of the weld, and the welded joints showcasing a better integral corrosion property than that of 304 base metals. Laser welding Ni-based alloy/austenitic stainless steel with filler wire has significant technical advantages for end sealing of nuclear reactor pump can.

Comparative study on microstructure and properties of laser welding and argon arc welding Hastelloy C-276/SS304 with filler wire

Comparative study on microstructure and properties of laser welding and argon arc welding Hastelloy C-276/SS304 with filler wire

Research on Microstructure and Mechanical Properties of Laser Welding of BR1500HS Joints

In this research, BR1500HS high strength steel was laser welded under various process parameters. The welded samples were heated in a furnace for 5 min with a temperature of 900 °C and then water-quenched. The effects of process parameters and quenching process on mechanical properties and microstructure of the joints were investigated. The results show that when the heat input is 1440 J/cm, the best mechanical properties of the welded joint can be obtained. When the welding speed increases, the minimum hardness increases, and the width of the softened area decreases; while the laser power increases, the width of the softened area increases, and the minimum hardness does not change significantly. As the welding speed increases, the front-bead width A, back-bead width B, and the height of smooth segment H all decrease; while the laser power increases, the back-bead width B increases, the front-bead width A and the height of the smooth segment H increase first and then decrease. The front-bead width A reaches the maximum when the laser power is 3000 W and the height of the smooth segment H does not change much.

Laser dissimilar welding of Al/Mg lap-joint with Ti interlayer through optimized 8-shaped beam oscillation

Due to the advantages to enlarge action range of laser and induce stirring effects on molten pool, beam oscillation is proven to improve the gap tolerance and mechanical properties of laser welds. However, the commonly used circular beam oscillation still has shortcomings in the uniformity of laser energy distribution and the ability to control melt flow. In the current study, a novel 8-shaped beam oscillation was adopted to solve the uneven heating and reaction at interface in laser circular oscillating welding of Al/Mg lap-joint with Ti as interlayer. The uniformity of laser energy distribution was improved by 60 % when the beam oscillating pattern changed from circle to 8-shaped. The homogenized laser energy distribution benefited to fully melt the Ti interlayer at interface and increase the connection width of interface from 0.6 to 2.4 mm. These improvements enhanced the shear tensile force of Al/Mg lap-weld up to 4.4 kN, increased by 3.8 times compared to laser circular oscillating welding.

Effect of filler Al-Mg-Mn wire and post-heat treatment on the structural-phase state and mechanical properties of laser welding of Al-Mg-Li alloy

In this work, complex studies of laser welding using filler aluminum wire of the Al-Mg-Mn system and post weld heat treatment were carried out in order to increase the level of mechanical properties of alloys of the Al-Mg-Li system. High-quality weld joints were obtained. The use of synchrotron radiation with a spatial resolution of 100 μm made it possible to scan the weld and the original alloy in detail. Subsequent heat treatment of the weld made it possible to form the strengthening phase δ'(Al3Li) and improve the mechanical properties. Energy conditions for obtaining a high-quality weld with wire: heat input ≈ 90.9 J/mm, energy per unit volume of the molten material ≈ 28.94 J/mm3.

Effect of pulse overlap rate on the microstructure and mechanical properties of laser welds of thin AZ31 magnesium alloy

In order to improve the quality of pulsed laser welding on magnesium alloy, the effect of pulse overlap rate on the microstructure and mechanical properties of the welds is studied. A Nd:YAG pulsed laser welding machine is used to carry the butt welding experiments on AZ31 magnesium alloy (1 mm), and the pulse overlap rate (10%, 30%, 50%, 70%, 90%) is varied by adjusting the welding velocity. The experimental results show that with the increases of pulse overlap rate, the sensitivity of the solidification cracks and pores decreases. The grain size of the columnar grains at the fusion boundary (FB) and the equiaxed grains in the center of the welds increases and then decreases and reach the maximum value of 114.72 ± 3.06 μm and 74.08 ± 5.87 μm, respectively, when the overlap rate is 70%. The percentage of the ductile fracture in the fracture of tensile specimens is proportional to the pulse overlap rate. With the increases of the pulse overlap rate, the tensile strength and maximum force show a trend of decreasing first and then increasing, and both reach the maximum value of 94.583 MPa and 1.135 kN when the overlap rate is 90%. Besides, the microhardnesses of the welds decrease first and then increase, and it’s maximum value is 86 HV0.2. In summary, the welds with better surface morphology can be obtained at the pulse overlap rate of 70%, while the mechanical properties of the welds are better when the overlap rate is 90%.

Microstructure and mechanical properties of dissimilar laser welding of NiTi to copper

ABSTRACT This paper characterises the dissimilar laser welding of 0.5 mm thick plate of shape memory alloy (NiTi) and copper (Cu) at different welding speeds. Properties of laser welds are characterised by microhardness testing, tensile-shear testing, XRD analysis, differential scanning calorimetry (DSC), and optical microscopy. XRD analysis of welded zone demonstrates the presence of NiTi, Cu, and equiatomic NiTi-Cu phases due to diffusion of NiTi and Cu at the interfacial zone of NiTi-Cu joint. DSC analysis shows the start and finish temperature of austenite phase during heating and martensitic phase during cooling for NiTi and laser welded sample. Microhardness studies reveal that weld zone possesses much higher hardness than NiTi and Cu base alloy. Microhardness value at NiTi-Cu joint interface (fusion zone) increases to 280HV and 150HV because of the presence of brittle and hard IMC phases (i.e. NiTiCu). The welded joints deliver higher joint strength than Cu base alloy but lower strength than NiTi SMA. Maximum joint strength of 335MPa (strain of 13.6%) is achieved at 1400W laser power and 1 m/min welding speed due to improved mixing and material flow. Microstructures of the fusion zone have dendrites grains and show the presence of Cu and NiTi constituents in the weld region.

Influence of Welding Process on Microstructure and Properties of Laser Welding of SiCp/6061 Al Matrix Composite

Direct laser welding, laser welding with Ti interlayer, and ultrasonic-assisted laser welding with Ti interlayer were used to join SiCp/6061 Al matrix composites. Microstructural evolutions, compositional distributions and tensile strengths under three processes were compared and analyzed. The experimental results showed that ultrasonic-assisted laser welding with Ti interlayer can obtain joints with good continuity and without obvious defects. Due to combined effects of Ti interlayer and ultrasonic, formation of brittle Al4C3 phase was greatly suppressed and fine TiC precipitates were also uniformly distributed in weld metal. The strength shown by the welded joints could reach up to 77.2% of the strength of the base material. Because of the internal defects (voids and pores) and the generated large numbers of brittle phases of Al4C3 in weld metal, the joint strength shown by the other two techniques, direct laser welding and laser welding with Ti interlayer, only reached 49.4 and 64.8% of the base material strength, respectively.

Microstructure and mechanical properties of laser welding of AZ31B magnesium alloy and DP590 dual-phase steel with concave groove joint

A novel connection method has been explored for laser welding of AZ31B magnesium alloy and DP590 dual-phase steel, where lap joint with concave groove was added by Sn powder. The influence of groove width on the interface reaction and mechanical properties of the joint was also studied. The result show that the boundary surface of the concave groove was mainly divided into two regions. One was the laser directly irradiated area which was mainly composed of FeAl + Mg2Sn + α-Mg. As the width of the concave groove increased, the phase composition of the interface changed from FeAl + Mg2Sn + α-Mg to FeAl + FeSn + Mg2Sn + α-Mg. The other was the side boundary area of the concave groove, where a large amount of Sn was transferred from the directly irradiated area, thus the columnar Mg2Sn + α-Mg crystal grains were larger than the directly irradiated area. This interface was mainly composed of FeAl + Mg2Sn + α-Mg. The calculation results of the atomic chemical potential were shown that the Al atoms from the base material diffused to the Fe side in the Mg-Al-Sn-Fe system, which made it easier to form the FeAl phase at the interface. At the Fe interface, Fe and Sn atoms were attracted by Al atoms, which promoted the reaction between Fe atoms and Sn atoms. The maximum load value reaches 1711 N with 1.5 mm width of concave groove, representing twice enhancement compared with that with no-concave groove.

Numerical study on the effect of residual stress on mechanical properties of laser welds of aluminum alloy 2024

The fusion zone is the weak area of weld joint which will experience complex thermal mechanical process during laser welding aluminum alloy 2024-T4. The resulting residual stress in the weld joint may exceed the yield stress, which will significantly affect the hardness and tensile strength. The purpose of this study is to predict the residual stress, and analyze its relationship with hardness and yield stress of the aluminum alloy 2024-T4 weld joint. Herein, three sequential models are established: (i) a thermal finite element model using double cone combined heat source that allows the prediction of time-dependent temperature distribution during laser welding of aluminum alloy 2024; (ii) a mechanical model using sequential coupling method and loading temperature in each increment to predict strain and residual stress; (iii) a theoretical empirical model to link the residual stress, hardness and yield stress. The simulated temperature field from the thermal model is in good agreement with the experimental result. The predicted stress field shows that the average von Mises stress at the center of the Al 2024-T4 and Al 2024-O weld joints are 303.60 MPa and 62.85 MPa, respectively, which are close to their yield stress. Moreover, it is found that the hardness decreases by 6 HV0.1 under the influence of residual stress in Al 2024-T4 fusion zone. The results indicate that the yield stress of 2024-T4 weld joint decreases by 16.5 MPa as a result of the residual stress. Above results indicate that residual stress has non-negligible influences on the mechanical properties of laser weld joint.

Analysis of Ni interlayer effects on laser beam welding of dissimilar pure Mo alloy to stainless steel

The effect of Ni interlayer thickness on chemical composition, microstructure and mechanical properties of laser welding of Mo and stainless steel was analyzed systematically. Experimental results indicated that with the increase in thickness of Ni interlayer, the number of MoFe IMCs, the hardness at the Mo-FZ interface, the width and grain size in the heat affected zone of Mo side and the thickness of MoFe IMCs layer decreased significantly. The maximum tensile strength attained 351 MPa for joints with 0.1 mm thick Ni interlayer. With excessive (>0.1 mm) Ni addition in the welded joint, the mechanical properties deteriorated due to the formation incomplete fusion, void and crack defects. The tensile investigation showed that the weakest area of the joint was MoFe IMCs layer. When an appropriate thickness of Ni interlayer is used, the MoFe IMCs layer can be strengthened by increasing diffusion ability of Mo to FZ and Ni concentration in the MoFe IMCs and restraining of MoFe IMCs, consequently producing high-quality welded joints.

The laser welded joints properties of cryogenic austenitic nitrogen-containing steel*

ABSTRACT Formation, structure and properties of welded joints in cryogenic austenitic nitrogen containing steel of chromium – nickel – manganese – nitrogen alloying system with reduced nickel content are investigated. Under optimal laser welding conditions, a weld of small width with almost parallel walls is formed. This helps to reduce residual stresses and strains. There is a significant reduction in the structure size parameters of the weld compared to arc welding. The mechanical properties of laser welds are within acceptable limits, so the tensile strength is 0.84–0.96 of the base metal. Fractographic analysis of the fracture surface of welded samples after testing showed the presence of developed zones of plastic deformation, which characterizes the laser-welded joint as highly plastic.

Shape Memory Characteristics in Welded SMA Alloys

This paper mainly studies the laser welding properties of shape memory alloys. Phase transformation of the laser welded SMA alloys was investigated through XRD and DSC. The stress-strain behaviors and shape memory effects of the laser weld joints were investigated with tensile tests at room temperature or variable temperature, respectively. DSC test project is the result of the effect and influence of the test welding process on the heat affected zone. The results show that laser welding alloy is beneficial to the refinement of weld structure and improves the mechanical properties and shape memory of weld.

Multi-response optimization of mechanical properties of laser welds of PP/EPDM/clay nanocomposite using response surface methodology based on desirability approach analysis

Laser welding and nanocomposites are finding increasing applications in industries. The polypropylene/ethylene-propylene-diene-monomer/clay nanocomposite has wide application in many industries. In this study, the effect of laser power, standoff distance, scan velocity, and clay content as input parameters on tensile and impact strengths of laser welds and welding operation cost as output parameters has been investigated using response surface methodology. The Box–Behnken design was employed to establish proper mathematical models relating input to output parameters. Morphology and dispersion of clay in the above nanocomposite have also been evaluated by X-ray diffraction and transmission electron microscopy. The results have been presented numerically and graphically. The results show that with laser power of 108.84–110.90 W, scan velocity of 566.18–597.19 mm/min, standoff distance of 8 mm, and clay content of 0.35–0.83 wt%, optimum values for tensile strength of 9.3 MPa, impact strength of 67.2 J/m, and welding cost of 30 cents/m are obtained. A minimum cost weld (18.5 cents/m) can be achieved when a proper combination of laser power of 108.53–109.80 W, scan velocity of 874.27–893.09 mm/min, standoff distance of 8 mm, and clay content of 0.75–0.94 wt% is selected.

The Comparison between Mechanical Properties of Laser-Welded Ultra-High-Strength Austenitic and Martensitic Steels

The paper investigates experimentally the usability of ultra-high-strength stainless steel and abrasion resistant steel in laser-welded sandwich structures. The fatigue and shear strength of laser joints were investigated using lap joints that were welded using two very different energy inputs. Also the effect of multiple weld tracks was investigated. The properties of separate laser welds were characterized by hardness testing and optical microscopy. Results of the hardness measurements showed that there was softened area at heat-affected-zone and weld metal of the ultra-high-strength stainless steel welds. AR steels weld metal was harder than base metal and there was softened zone in heat-affected-zone of the weld. The shear strength of tested single weld joints of the ultra-high-strength stainless steel was higher compared abrasion resistant steel single weld joints, but stronger joint can be made with multiple weld seams for abrasion resistant steel. Fatigue strength of investigated ultra-high-strength stainless steel lap joint was lower than fatigue strength of abrasion resistant steel lap joint in the low-cycle regime, but there was no practical difference in fatigue limit (10e7 cycles).

Effect of laser offset on microstructure and mechanical properties of laser welding of pure molybdenum to stainless steel

Direct welding of Mo and stainless steel is exceptionally difficult due to intrinsic brittleness of Mo and the formation of brittle Fe-Mo phases. To explore the feasibility of welding of Mo and stainless steel, the laser offset method was used in this study. Experimental results show that the offset of the laser beam toward stainless steel has a positive effect for the quality of Mo/Fe dissimilar joint. As the laser beam shifts from the Mo side to the stainless steel side, the formation of welding defects and Fe-Mo intermetallic compounds (IMCs) are effectively restricted because of the decrease amount of molten Mo. The decrease of Fe-Mo IMCs contributes to the reduction of hardness in the joints. With an increase of laser offset, the thickness of Fe-Mo IMCs layer decreased, consequently the tensile strength of joints increased first and then decreased in the laser offset range of 0.2–0.5 mm. The highest tensile strength of the joints is 290 MPa at the laser offset of 0.3 mm. All joints failed in the Fe-Mo IMCs layer with brittle fracture mode during tensile tests, indicating the weakest zone of the joint was Fe-Mo IMCs layer. A sound weld of Mo and stainless steel can be obtained if an appropriate thickness of Fe-Mo IMCs layer is produced by adjusting the laser offset.

Microstructure and mechanical properties of laser welding of Ti6Al4V to Inconel 718 using Nb/Cu interlayer

Abstract To improve the quality of the joints between Ti6Al4V and Inconel 718, fiber laser welding with Nb/Cu multi-interlayer was attempted by laser welding induced brazing-welding method. The hybrid joint comprising different metallurgical areas was created based on fusion welding and brazing welding mechanisms through one welding. Ti6Al4V and Nb well bonded by the fusion welding, and the fusion zone was characterized by the formation of (α + β Ti, Nb) solid solutions. Nb and Inconel 718 were joined by brazing because of the melting of Cu foil, and the Nb/Cu/Inconel 718 interface mainly consisted of the Nb-based, Cu-based, and Ni-based solid solutions. The joint failed in the Nb/Cu/Inconel 718 interface with the maximum strength of 260 MPa, exhibiting brittle-like failure behavior due to the formation of voids and microcracks at the Nb/Cu/Inconel 718 interface. The addition of Nb/Cu multi-interlayer can help prevent the formation of IMCs and improves the mechanical properties of the joint.

Tensile and fatigue properties of laser-welded ultra-high-strength stainless spring steel lap joints

The study was performed to investigate the usability of thin 0.3 mm thick ultra-high-strength stainless spring steel in laser-welded simple panel structures. The mechanical properties of the laser welded joints in lap-shear specimens were investigated. The fatigue and shear strength of laser joints were experimentally investigated using continuous and intermittent lap joints that were welded using various energy inputs. The properties of separate laser welds were characterized by hardness testing and optical microscopy.Results of the hardness measurements showed that there was softened area at heat-affected-zone of the welds. Due to the weld mismatch, significant strain hardening took place at the weld seams. The shear strength of tested continuous lap joints was slightly lower compared to the yield strength of the base material. Fatigue strength of the studied lap joints was at acceptable level for dynamically loaded simple panel structures and the fatigue strength of the weld seams was in practice dependent on the weld area instead of weld type.

Numerical simulation optimization for laser welding parameter of 5A90 Al-Li alloy and its experiment verification

Weight reduction is very important to aircraft. Laser welding technology is beneficial to reduce the weight of aircraft structure. However, due to the unclear laser welding properties of Al-Li alloy, the research on laser welding of Al-Li alloy is necessary. In current study, the temperature field, stress field and deformation of laser welding are simulated. The optimal welding parameters are obtained by simulation, which are used to weld the real Al-Li alloy sheet. Besides, the microstructure and mechanical property of welded joints are analyzed. It is found that the simulated optimal welding parameters are suitable for welding real Al-Li alloy sheet. And the simulation results are consistent with the experimental results.