Laser Welding-brazing Process Research Articles

Laser welding-brazing under temporal and spatial power modulation for dissimilar materials AA6061 to Ti6Al4V joints

A novel laser welding-brazing process with temporal and spatial power modulation was firstly reported to join dissimilar alloys of AA6061 and Ti6Al4V with medium thickness. The power modulation was achieved by changing laser power as the same time as laser beam oscillating. A sound welded-brazed joint with relatively uniform intermetallic compound morphology along the Ti/Al interface was obtained. A multi-physical model was also developed and utilized to understand the underlying mechanism of the benefit of the temporal and spatial power modulation. It was found that the temperature gradient along the Ti/Al interface was reduced effectively by using this novel process.

Microstructure and tensile properties of Ti/Al dissimilar joint by laser welding-brazing at subatmospheric pressure

In this paper, the Ti6Al4V and 6061 Al dissimilar joints were welded by laser welding-brazing process, and the effect of subatmospheric pressure and laser offset on weld formation, porosity defect, intermetallic compounds (IMCs) distribution, and tensile properties of Ti/Al dissimilar joints was investigated in detail. At a subatmospheric pressure of 101 Pa and laser offset of 0.5 mm, a sound weld formation with full penetration was obtained. The porosity defect in the fusion zone was significantly eliminated and the thickness of IMCs layer was controlled less than 2 μm due to the enhanced melt flow and uniform temperature field at low vacuum. The tensile strength reached a maximum value of 181.1 MPa with a mixed-mode of ductile and brittle fracture.

Effect of laser beam models on laser welding–brazing Al to steel

Joining dissimilar metals Al to steel in butt configuration was successfully realized by laser welding–brazing process with different laser beam models (single laser beam, cross and in–line dual laser beams). Undercut occurred at the joint produced by single laser beam and satisfactory weld formations were obtained in the joints produced by cross and in–line dual laser beams. Dual laser beam was beneficial for the reduction of interfacial intermetallic compound (IMC) thickness and homogenization of interfacial IMC morphology. Numerical models were developed to calculate the thermal cycles along brazing interface. Calculation of interfacial thermal cycles revealed that lowest peak temperatures (1028 °C, 1036 °C and 990 °C respectively for top, middle and bottom regions), shortest time of interaction at high temperature (2.2 S) and smallest temperature gradients (1036–990 °C = 46 °C) were all obtained in the joint produced by cross dual laser beam and these all made contribution to its thinnest and most homogeneous interfacial IMC. Joint with the highest tensile strength was produced when the cross dual laser beam was adopted due to its satisfactory weld formation and most homogeneous of τ5.

Comparative study on the joining performance of TiH2 and ZrH2 modified AgCu28 brazing alloys with pulsed laser welding-brazing

Brazed alloys between cubic boron nitride (cBN) grits and matrix extremely affect the service life of the grinding wheel. The aim of this study was to investigate the addition of elemental Zr to improve the connection effect of alloys. The plates of pure titanium (Ti) Gr. 1 and AISI 1045 steel had been applied to conduct the welding-brazing experiments with active brazing alloys of AgCu28-4.5Ti and AgCu28-4.5Ti-4Zr. Brazing alloys was heated with an Nd:YAG pulsed laser welding-brazing system under inert argon gas atmosphere. Transition zones between the brazed alloys and matrices were investigated with scanning electron microscope (SEM), energy dispersion spectrometer (EDS), and X-ray diffraction (XRD) analyses. In addition, hardness of the brazed layer was analyzed as well as tribology. The results showed that the active element, zirconium (Zr), significantly accelerated the bidirectional diffusion and improved the gradient evolution of the main elements in the transition zones. Compared to Zr-free brazing alloys, the active element, Zr, inhibited the overproduction of the hard-brittle phase of Cu3Ti and formed other intermetallic compounds, such as AgZr2 and Cu10Zr7, which were beneficial to the metallurgical joint. A brazed layer with a lower friction coefficient, a more uniform hardness distribution, and better ductility was obtained, though the wear resistance slightly decreased. A solid solution product of Zr-Cu was formed during laser welding-brazing process, which strengthens the brazed layer and improves its overall performance.

The Study on Mechanical Strength of Titanium-Aluminum Dissimilar Butt Joints by Laser Welding-Brazing Process

Laser welding–brazing of 5A06 aluminum to Ti6Al4V titanium in a butt configuration was carried out to discuss the influences of welding parameters on dissimilar joint properties. The effects of laser offset, welding speed, and laser power on the spreading length of the molten aluminum liquid, interface fracture zone width (IFZW), fracture roughness, intermetallic compounds (IMCs) thickness, and tensile strength were also investigated. The microstructure and fracture of the joint were also studied. The results show that the tensile strength of the joint is not only influenced by the thickness and type of IMCs, but also influenced by the spreading ability of the aluminum liquid, the fracture area broken at the Ti/fusing zone (FZ) interface, and the relative area of the brittle and ductile fracture in FZ. A dissimilar butt joint with an IMC thickness of 2.79 μm was obtained by adjusting the laser offset, welding speed, and laser power to 500 μm, 11 mm/s and 1130 W, respectively. The maximum tensile strength of the joint was up to 183 MPa, which is equivalent to 83% of the tensile strength of the 5A06 aluminum alloy.

Temperature field simulation and grain morphology on laser welding-brazing between Ti-6Al-4V and 1050 aluminum alloy

Laser welding-brazing (LWB) technique is considered to offer advantages over fusion welding in terms of dissimilar jointing since it can avoid liquid dissimilar alloys mixing in the molten pool. In this paper, LWB technique is utilized to join 1050 aluminum alloy to Ti-6Al-4V. A 3D finite element model is developed to calculate the temperature field in the LWB process with a combined Gaussian heat source model. The simulated asymmetric temperature field is in good agreement with the experimental metallography, which confirms the validity of the present combined heat source model. The peak temperature of the center of the weld seam increases with time in the welding process. The experimental and simulation results both indicate that the heat-affected zone (HAZ) width of the upper is narrower than that of the bottom. Besides, the growth orientation of coarsened dendrite near the interface at root face is substantially perpendicular to interface. The grain morphology of the molten pool appears as dendrite, cellular dendrite and equiaxed crystal from the fusion line to the center of the weld seam.

Effect of the Ni coating thickness on laser welding-brazing of Mg/steel

Dissimilar AZ31B-Mg and Ni-coated Q235A-steel alloys were joined in a lap configuration using a laser welding-brazing process. The effects of the Ni coating thickness on the joint appearance, interfacial reactions and mechanical properties were investigated with the assistance of thermodynamic calculations. In the direct irradiation region, Ni atoms diffused and were accumulated near the interface due to the driving force of the chemical potential. Al atoms from the filler were attracted by the concentrated Ni atoms, which resulted in the formation of the FeAl phase. In the middle region and weld toe region, a Fe(Ni) solid solution formed at the interface. Heterogeneous reaction products were produced at the seam near the interface, varying from only the AlNi phase to the AlNi+(α-Mg+Mg2Ni) eutectic with the increase of the coating thickness. Additionally, a bulky Mg2Ni phase also formed in the matrix of Mg-Ni eutectic with a coating thickness of 40 μm. Strong mutual attraction occurred between the Al and Ni atoms at the seam, resulting in a higher driving force for generating the AlNi phase than for generating the Mg-Ni phase. All joints were finally fractured at the seam. The maximum value of the tensile-shear fracture load approached 230 N/mm with a Ni coating thickness of 20 μm, reaching an 88.5% joint efficiency relative to the Mg base metal.

Influence of Ni-coating thickness on laser lap welding-brazing of Mg/Ti

Dissimilar lap joining of magnesium alloy to titanium alloy was performed using Ni coating by laser welding-brazing process. The influence of different Ni-coating thicknesses on microstructure and mechanical properties were investigated. In laser irradiation region, Ti3Al phase formed at fusion zone/Ti interface. In middle region, Ti3Al phase still existed at fusion zone/Ti interface, while Mg-Al-Ni ternary IMC generated at fusion zone. In weld toe region, Ti-Ni binary IMC were observed at the interface of fusion zone/Ti. The particles of Mg-Al-Ni ternary compound grew bigger and thickness of Ti-Ni compound layer increased with the increase of Ni-coating thickness. TiNi IMC transformed into (TiNi + Ti2Ni) mixtures when the Ni-coating thickness exceeded 5.8 μm. Interfacial microstructure evolution was clarified according to thermodynamic calculation results of formation enthalpy and chemical potential. The fracture load first increased and then decreased slightly with increasing coating thickness, the maximum fracture load (2430 N/cm) represented 90% joint efficiency in relation to the Mg base metal. The fracture mode changed from interfacial failure into fusion zone fracture when the Ni-coating thickness was greater than 4.0 μm. The interfacial bonding were relatively low, while the performance of fusion zone fracture was relatively high. Further increase of coating thickness has little effect on the performance deterioration. The bonding mechanism of Mg to Ni-coated Ti were illuminated.

Effect of Si content on the interfacial reactions in laser welded-brazed Al/steel dissimilar butted joint

6061-T6 aluminum alloy and DP590 steel were joined successfully by a laser welding–brazing process with pure Al, AlSi5, and AlSi12 filler metals. Interfacial microstructure of the joints with highest tensile strength (under laser powers of 2000 W, 2000 W and 2500 W for joints obtained with pure Al, AlSi5 and AlSi12 filler metals, respectively) were selected for comparison. The interface produced with the pure Al filler metal consisted of a thick layer of η-Fe2Al5 with scattered rod-shaped θ-FeAl3, with average thicknesses of 10.1 μm in the bottom region and 16.7 μm in the top region. When 5 wt.% Si was added to the filler metal, the interfacial intermetallic compound (IMC) components remained similar, whereas the interface thickness decreased to 3.8 μm in the bottom region and 7.5 μm in the top region. On further increasing the Si addition to 12 wt%, the interfacial IMC acquired 1.2 μm-thick τ5-Fe2Al8Si in the bottom region with 5.6-μm-thick θ-Fe(Al,Si)3 and τ5-Fe2Al8Si in the top region. The chemical potential of Si in the Fe-Al-Si ternary system was lower at the Fe-Al side comparing with weld seam and steel substrate, which led to a preferentially diffusion of Si to the Fe/Al interface and finally caused the aggregation of Si in the Fe/Al interface. Si addition improved the joint strength and reduced the required laser power for a suitable joint. The joint produced with the AlSi5 filler metal had the highest tensile strength and largest fracture displacement.

Laser Welding-Brazing of Immiscible AZ31B Mg and Ti-6Al-4V Alloys Using an Electrodeposited Cu Interlayer

Metallurgical bonding between immiscible system AZ31B magnesium (Mg) and Ti-6Al-4V titanium (Ti) was achieved by adding Cu interlayer using laser welding-brazing process. Effect of the laser power on microstructure evolution and mechanical properties of Mg/Cu-coated Ti joints was studied. Visually acceptable joints were obtained at the range of 1300 to 1500 W. The brazed interface was divided into three parts due to temperature gradient: direct irradiation zone, intermediate zone and seam head zone. Ti3Al phase was produced along the interface at the direct irradiation zone. Ti-Al reaction layer grew slightly with the increase in laser power. A small amount of Ti2(Cu,Al) interfacial compounds formed at the intermediate zone and the (α-Mg + Mg2Cu) eutectic structure dispersed in the fusion zone instead of gathering when increasing the laser power at this zone. At the seam head zone, Mg-Cu eutectic structure was produced in large quantities under all cases. Joint strength first increased and then decreased with the variation of the laser power. The maximum fracture load of Mg/Cu-coated Ti joint reached 2314 N at the laser power of 1300 W, representing 85.7% joint efficiency when compared with Mg base metal. All specimens fractured at the interface. The feature of fracture surface at the laser power of 1100 W was characterized by overall smooth surface. Obvious tear ridge and Ti3Al particles were observed at the fracture surface with increase in laser power. It suggested atomic diffusion was accelerated with more heat input giving rise to the enhanced interfacial reaction and metallurgical bonding in direct irradiation zone, which determined the mechanical properties of the joint.

Effect of filler wire composition on performance of Al/Galvanized steel joints by twin spot laser welding-brazing method

A twin-spot laser welding-brazing (LWB) process to join aluminum alloy 6022 and hot-dip galvanized steel in coach peel configuration was reported. A maximum surface roughness and sufficient mechanical strength are the important criteria which are affected by the process parameters during welding to judge the weld quality for some applications, such as the automotive industry. Thus, the influences of the main laser welding-brazing process parameters (laser power, wire feed rate, and scanning speed) on the mechanical strength and surface roughness of welds were studied and analytical models relating the output properties of interest to process parameters were also developed. The response surface methodology (RSM) and desirability function were utilized for optimizing the multi-response LWB process. Finally, validation experiments were conducted on an optimized process condition which exhibited good agreement between the predicted and experimental results. Four different filler wire materials were employed (AlSi12, AlSi5, AlSi3Mn1, and ZnAl15). The effects of the wire alloying elements on the microstructure of the weld, weld surface quality, and mechanical resistance were investigated. The measured intermetallic compound, IMC, layer at the Fe/Al interface of joints revealed that AlSi12 filler wire resulted in the thinnest IMC layer at less than 2μm; in contrast, this value increased to 7μm for joints with ZnAl15 wire. In terms of surface roughness, the lowest (Ra=0.917μm) and highest (Ra=2.83μm) values were achieved by using AlSi3Mn1 and ZnAl15 wires, respectively. Although the Zn-based filler wire offered the maximum tensile resistance around 180N/mm, joints with AlSi12 wire had mechanical resistance of 120N/mm and lower values of IMC layer thickness and surface roughness. Therefore, AlSi12 filler material is recommended as the laser brazing filler material for joining dissimilar aluminum-galvanized steel coach peel panels in automotive body-in-white (BIW) fabrication applications.

Effect of welding speed on microstructural evolution and mechanical properties of laser welded-brazed Al/brass dissimilar joints

Laser welding-brazing process was developed for joining 5052 aluminum alloy and H62 brass in butt configuration with Zn-15%Al filler. Effect of welding speed on microstructural characteristics and mechanical properties of joints were investigated. Acceptable joints without obvious defect were obtained with the welding speed of 0.5–0.6m/min, while lower and higher welding speed caused excessive back reinforcement and cracking, respectively. Three reaction layers were observed at welding speed of 0.3m/min, which were Al4.2Cu3.2Zn0.7 (τ′)/Al4Cu9/CuZn from weld seam side to brass side; while at welding speed of 0.4–0.6m/min, two layers Al4.2Cu3.2Zn0.7 and CuZn formed. The thickness of interfacial reaction layers increased with the decrease of welding speed, but varied little at different interfacial positions from top to bottom in one joint. Tensile test results indicated that the maximum joint tensile strength of 128MPa was obtained at 0.5m/min, which was 55.7% of that of Al base metal. All the joints fractured along the weld seam/brass interface. Some differences were found regarding fracture locations with three and two reaction layers. The joint fractured between Al4Cu9 and τ′ IMC layer when the interface had three layers, while the crack occurred between CuZn and τ′ phase in the case of two layers.

Effect of dual laser beam on dissimilar welding-brazing of aluminum to galvanized steel

In this investigation, the joining of two types of galvanized steel and Al6022 aluminum alloy in a coach peel configuration was carried out using a laser welding-brazing process in dual-beam mode. The feasibility of this method to obtain a sound and uniform brazed bead with high surface quality at a high welding speed was investigated by employing AlSi12 as a consumable material. The effects of alloying elements on the thickness of intermetallic compound (IMC) produced at the interface of steel and aluminum, surface roughness, edge straightness and the tensile strength of the resultant joint were studied. The comprehensive study was conducted on the microstructure of joints by means of a scanning electron microscopy and EDS. Results showed that a dual-beam laser shape and high scanning speed could control the thickness of IMC as thin as 3µm and alter the failure location from the steel-brazed interface toward the Al-brazed interface. The numerical simulation of thermal regime was conducted by the Finite Element Method (FEM), and simulation results were validated through comparative experimental data. FEM thermal modeling evidenced that the peak temperatures at the Al-steel interface were around the critical temperature range of 700–900°C that is required for the highest growth rate of IMC. However, the time duration that the molten pool was placed inside this temperature range was less than 1s, and this duration was too short for diffusion-control based IMC growth.

Multiphysics Simulation and Experimental Investigation of Aluminum Wettability on a Titanium Substrate for Laser Welding-Brazing Process

The control of metal wettability is a key-factor in the field of brazing or welding-brazing. The present paper deals with the numerical simulation of the whole phenomena occurring during the assembly of dissimilar alloys. The study is realized in the frame of potential applications for the aircraft industry, considering the case of the welding-brazing of aluminum Al5754 and quasi-pure titanium Ti40. The assembly configuration, presented here, is a simplification of the real experiment. We have reduced the three-dimensional overlap configuration to a bi-dimensional case. In the present case, an aluminum cylinder is fused onto a titanium substrate. The main physical phenomena which are considered here are: the heat transfers, the fluid flows with free boundaries and the mass transfer in terms of chemical species diffusion. The numerical problem is implemented with the commercial software Comsol Multiphysics™, by coupling heat equation, Navier-Stokes and continuity equations and the free boundary motion. The latter is treated with the Arbitrary Lagrangian Eulerian method, with a particular focus on the contact angle implementation. The comparison between numerical and experimental results shows a very satisfactory agreement in terms of droplet shape, thermal field and intermetallic layer thickness. The model validates our numerical approach.

Simulation model of Al-Ti dissimilar laser welding-brazing and its experimental verification

Formation of dissimilar weld joints of light metals and alloys including Al-Ti joints is interesting mainly due to demands on the weight reduction and corrosion resistance of components and structures in automotive, aircraft, aeronautic and other industries. Joining of Al-Ti alloys represents quite difficult problem. Generally, the fusion welding of these materials can lead to the development of different metastable phases and formation of brittle intermetallic compounds. The paper deals with numerical simulation of the laser welding-brazing process of titanium Grade 2 and EN AW 5083 aluminum alloy sheets using the 5087 aluminum filler wire. Simulation model for welding-brazing of testing samples with the dimensions of 50 × 100 × 2 mm was developed in order to perform numerical experiments applying variable welding parameters and to design proper combination of these parameters for formation of sound Al-Ti welded-brazed joints. Thermal properties of welded materials in the dependence on temperature were computed using JMatPro software. The conical model of the heat source was exploited for description of the heat input to the weld due to the moving laser beam source. The sample cooling by convection and radiation to the surrounding air and shielding argon gas was taken into account. Developed simulation model was verified by comparison of obtained results of numerical simulation with the temperatures measured during real experiments of laser welding-brazing by the TruDisk 4002 disk laser.

Influence of laser power on microstructure and mechanical properties of laser welded-brazed Mg to Ni coated Ti alloys

AZ31B Magnesium (Mg) and Ti-6Al-4V titanium (Ti) alloys with Ni coating were joined by laser welding-brazing process using AZ92 Mg based filler. The influence of laser power on microstructure and mechanical properties were investigated. Ni coating was found to significantly promote good wetting-spreading ability of molten filler on the Ti sheet. Acceptable joints without obvious defects were obtained within a relatively wide processing window. In the process metallurgical bonding was achieved by the formation of Ti3Al phase at direct irradiation zone and Al-Ni phase followed by a layer of Mg-Al-Ni ternary compound adjacent to the fusion zone at the intermediate zone. The thickness of reaction layers increased slowly with the increasing laser power. The tensile-shear test indicated that joints produced at the laser power of 1300W reached 2387N fracture load, representing 88.5% joint efficiency with respect to the Mg base metal. The corresponding failure occurred in the fusion zone of the Mg base metal, while joints fractured at the interface at lower/higher laser power due to the crack or excessive intermetallic compound (IMC) formation along the interface.

Microstructure and mechanical properties of laser welded-brazed Mg/Ti joints with AZ91 Mg based filler

AZ31B Magnesium (Mg) alloys and Ti-6Al-4V titanium (Ti) alloys were joined by laser welding-brazing process with AZ91Mg based filler. Uniform and continuous weld surfaces without obvious defects were produced in a relatively large processing window. In the process Al element diffused from the filler and reacted with Ti resulting in metallurgical bonding of Mg/Ti joint. An ultra-thin reaction layer with serrate-shaped morphology was evidently observed at the interface of AZ91 fusion zone/Ti. The thickness was varied slowly with the change of the heat input. Newly formed interfacial compound was then identified as Ti3Al phase by transmission electron microscopy (TEM) analysis. The maximum tensile-shear strength reached 2057N, representing 50% joint efficiency relative to Mg base metal. Two kinds of fracture modes were noticed during the tensile-shear test. Observation of fracture surfaces suggested some reaction products were attached to Ti substrate in both cases, which was found to prevent crack propagation effectively and thus improved the joint strength.

Enhanced interfacial reaction and mechanical properties of laser welded-brazed Mg/Ti joints with Al element from filler

Dissimilar metal joining between magnesium and titanium alloys was performed using laser welding-brazing process. Metallurgical bonding of immiscible AZ31 magnesium and TC4 titanium was successfully achieved by adding Al element into Mg based filler, compared to mechanical bonding when direct joining. An ultra-thin serrated-shape reaction layer was evidently observed at the interface of AZ91 (9%Al) fusion zone/Ti and identified as Ti3Al phase by transmission electron microscopy (TEM), which could prevent crack propagation effectively and thus improved the joint strength. The average fracture load of joint with AZ91 filler could reach 1947±61N representing 47.3±1.5% joint efficiency relative to the magnesium base metal, which was 85% higher than that with AZ31filler.

Laser welding-brazing of Mg to stainless steel: joining characteristics, interfacial microstructure, and mechanical properties

Magnesium alloy and stainless steel were joined by dual-beam laser welding-brazing process. The effect of the main process parameters including welding speed, wire feed speed, and heat input on weld appearance of the dissimilar joint was investigated. The microstructures of both welded and brazed side were observed using scanning electron microscopy (SEM) and identified by transmission electron microscopy (TEM). Mechanical properties were then studied. Formation of continuous thin reaction layer was observed along the fusion zone-steel interface, which was thereafter identified as FeAl intermetallic compound. The thickness was in the range of 0.9–2.9 μm, varied slowly with the increase of heat input. The tensile-shear test indicated that high joint strength was achieved at a wide range of heat input, with a maximum value of 274.5 N/mm, reaching 83.8 % of that of Mg base metal. The corresponding failure occurred in the heat-affected zone (HAZ) of the Mg base metal. While joints fractured at the interface or fusion zone at low/high heat input due to weak bonding or porosity formation at fusion zone.

Interface Microstructure in Laser Welding-Brazing of AZ31B/TC4 Dissimilar Alloys

The interface microstructure in the joints of magnesium alloy AZ31 to Ti alloy by the laser welding-brazing (LWB) process have been investigated in this paper. The results indicated that the interface between the solder reaction and TC4 formed net and holes, there was a 1~2 μm intermetallic compound layer. Al-Mg-Zn compounds generated and distributed in the solder reaction zone.