Laser Beam Welding Joints Research Articles

Investigation of welding parameters on microstructure and mechanical properties of laser beam-welded joint of 2060 Al–Cu–Li alloy

2060 Al–Cu–Li alloy plates with 2- and 1-mm thickness were welded by a fiber laser beam. The weld microstructure features and the mechanical properties such as microhardness and tensile strength of 2060 Al–Cu–Li alloy laser beam-welded joint were investigated to study the influence of welding parameters on the weld bead. By microstructure and mechanical property analysis, it is found that weld width as well as penetration depth increases with the increase of laser power when the welding speed is constant. The microstructures of the fusion line and fusion zone show similar dendrite morphologies with traditional cast structure under the thermal cycling. Fine grain zone can be observed near the fusion line. Welding porosities exist in the microstructure of 2060 Al–Cu–Li laser beam-welded joint. Porosity ratio increases at first, and then declines, and then increases again with the increase of laser power. The larger heat input causes the lower microhardness distribution of the corresponding joint. The optimized welding parameters of fiber laser beam welding of 2- and 1-mm-thick 2060 Al–Cu–Li alloys are 2500 W and 3 m/min and 2300 W and 4 m/min, respectively.

Finite element analysis of laser beam-welded butt joints

Thermal distortion of tailored blanks (TBs) during welding usually leads to a poor formability in the subsequent plastic deformation of TBs, and the welding distortion becomes especially serious in TBs consisting of different thickness plates. In this investigation, finite element method was applied to investigate the welding distortion of TBs with different thickness plates produced by laser beam welding. At the beginning, a 3D heat source model was built and verified by experimental results. Then, the following simulation results showed that the residual stresses generated in the thick plate side of the TBs were higher than those in the thin one. The varied reduction of heat input along the thickness direction for those two base plates can explain for this.

Effects of double-pass welding and extrusion on properties of fiber laser welded 1.5-mm thick T2 copper joints

The elongation of the laser beam welded joint is much lower than that of base metal due to the existence of softened zone and coarse columnar grain structures in the fusion zone. Mechanical extrusion can enhance the micro hardness of the softened zone in copper joint, whereas double-pass laser beam welding will disrupt the growth direction of the columnar grain structures in the fusion zone and decrease the size of columnar grains. Four types of copper joints were prepared, which included the single-pass laser beam welded (LBW) joint, single-pass laser beam welded+extrusion (LBW & E) joint, double-pass laser beam welded (DLBW) joint, and the double-pass laser beam welded+extrusion (DLBW & E) joint. The microstructure and mechanical properties of these four types of joints were characterized and compared. The results show that the mechanical properties of the DLBW & E joint exhibited the most pronounced improvement, where its tensile strength and elongation increased by 8.5% and 20.1% compared with those of the LBW joint, respectively. The extrusion process would increase the number of dislocations in the FZ of copper joints and consequently lead to a slight degradation of both thermal conductivity and electrical conductivity.

Evaluation of Residual Stresses and Mechanical Properties of IF Steel Welded Joints by Laser and Plasma Processes

Interstitial free (IF) steel has an extensive application in the automotive industry where the Laser Beam Welding (LBW) process is widely used due to its high productivity. Similarly, the other used process, Plasma Arc Welding (PAW), is characterized by a greater energy concentration and current density and therefore lower distortion, higher welding speeds and higher penetration may be obtained. However, while the traditional welding processes have been extensively studied with regard to the generation of residual stresses, there are few studies about residual stresses analysis and characterization of LBW and PAW joints. Therefore, the aim of the present work is to analyse the residual stresses resulting from LBW and PAW processes by X-ray diffraction technique with sin2ψ method in IF steel butt joints. For both joints, macro and microstructure were characterized and mechanical properties were determined. Tensile residual stresses in the heat-affected zone (HAZ) and in the fusion zone (FZ) were verified for both welding processes.

Fracture mechanical behaviour of laser beam-welded AA2198 butt joints and integral structures

Purpose– Composite materials and metallic structures already compete for the next generation of single-aisle aircraft. Despite the good mechanical properties of composite materials metallic structures offer challenging properties and high cost effectiveness via the automation in manufacturing, especially when metallic structures will be welded. In this domain, metallic aircraft structures will require weight savings of approximately 20 per cent to increase the efficiency and reduce the CO2emission by the same amount. Laser beam welding of high-strength Al-Li alloy AA2198 represents a promising method of providing a breakthrough response to the challenges of lightweight design in aircraft applications. The key factor for the application of laser-welded AA2198 structures is the availability of reliable data for the assessment of their damage tolerance behaviour. The paper aims to discuss these issues.Design/methodology/approach– In the presented research, the mechanical properties concerning the quasi-static tensile and fracture toughness (R-curve) of laser beam-welded AA2198 butt joints are investigated. In the next step, a systematic analysis to clarify the deformation and fracture behaviour of the laser beam-welded AA2198 four-stringer panels is conducted.Findings– AA2198 offers better resistance against fracture than the well-known AA2024 alloy. It is possible to weld AA2198 with good results, and the welds also exhibit a higher fracture resistance than AA2024 base material (BM). Welded AA2198 four-stringer panels exhibit a residual strength behaviour superior to that of the flat BM panel.Originality/value– The present study is undertaken on the third-generation airframe-quality Al-Li alloy AA2198 with the main emphasis to investigate the mechanical fracture behaviour of AA2198 BMs, laser beam-welded joints and laser beam-welded integral structures. Studies investigating the damage tolerance of welded integral structures of Al-Li alloys are scarce.

Microstructural characterisation and liquation behaviour of laser welded joint of fine grained AZ91 magnesium alloy thin sheets

Fine grained AZ91 sheets of 1 mm in thickness were successfully welded by autogenous laser beam welding and laser beam welding with filler strip. Both welded joints are characterised by fine equiaxed dendrites in the fusion zones and free from significant grain coarsening in the heat affected zones. There are two kinds of liquation reactions in the partially melted zone of the autogenous laser beam welding joint, which are associated with the melting of residual bulky β-Mg17Al12 phase and the constitutional liquation of submicrometre β-Mg17Al12 precipitates. No liquation reaction is detected in the welded joint obtained by laser beam welding with filler strip. The laser beam welding joint with filler strip for AZ91 thin sheets is free from evident collapse.

Laser welding effects on mechanical and fatigue properties of an Al-Cu-Li-Mg-Ag alloy

Development of idiosyncratic microstructure as a result of laser beam welding (LBW), and joint efficiency along with fatigue behaviour was investigated in an aluminium-lithium alloy. In this experiment rolled sheet of 2 mm thickness was used to fabricate butt joints via LBW technique. Five selected joints were analysed to observe the microstructural changes, mechanical and fatigue properties, and fracture mechanisms in the weld zone. Tensile test results showed that the LBW joints exhibited ∼21-30% reduction in UTS. However, a delayed fatigue crack initiation was observed inside the weld fusion zone, which was attributed to the freshly developed unique microstructure. A transgranular fatigue was detected in the near-threshold region, whereas, ductile striations during stage II, and intergranular dimpled fracture in the final stage. A fairly good fatigue life of the laser beam weld could be credited to the unique microstructural arrangement inside the fusion zone.

Review the Effect of Welding Processes on the Comprehensive Mechanical Properties of Magnesium Alloy Joints

In this paper, the effect of welding processes such as friction stir welding (FSW), laser beam welding (LBW) and pulsed current gas tungsten arc welding (PCGTAW) on comprehensive mechanical properties of AZ31B magnesium alloy was reviewed. Among the three different welding processes, the LBW joints showed superior comprehensive properties to FSW and PCGTAW joints. The formation of very fine grains in weld region, higher fusion zone hardness, uniformly distributed finer precipitates were the main reasons for superior comprehensive mechanical performance of LBW joints compared to PCGTAW and FSW joints.

Laser beam welding of aluminum to Al-base coated high-strength steel 22MnB5

The microstructure of aluminum—Al-coated steel laser beam welding joints was analyzed with respect to the welding energy. Quantitative and qualitative analysis of the welding microstructure were used to measure the weld width as well as the thickness of the resulting intermetallic layer at the 22MnB5/aluminum interface in relation to the welding parameters. Weldability of Al-coated steel could be improved by removing brittle coating particles and oxides on the steel surface by sandblasting. Adhesion of aluminum filler material to the 22MnB5 steel sheet could be enhanced by inductive preheating of the steel surface during laser welding. This produced welded 22MnB5/aluminum joints that exhibited a linear mechanical resistance of 220MPa and which failed away from the brittle intermetallic layer on the aluminum side under a tensile load. The shear strength of the intermetallic layer on the 22MnB5/aluminum interface was evaluated to 74±21MPa.

Comparison of Tensile Damage Evolution in Ti6A14V Joints Between Laser Beam Welding and Gas Tungsten Arc Welding

The present paper studied the evolution of tensile damage in joints welded using laser beam welding (LBW) and gas tungsten arc welding (TIG) under a uniaxial tensile load. The damage evolution in the LBW joints and TIG-welded joints was studied by using digital image correlation (DIC) technology and monitoring changes in Young’s modulus during tensile testing. To study the mechanism of void nucleation and growth in the LBW joints and TIG-welded joints, test specimens with various amounts of plastic deformation were analyzed using a scanning electron microscope (SEM). Compared with TIG-welded joints, LBW-welded joints have a finer microstructure and higher microhardness in the fusion zone. The SEM analysis and DIC test results indicated that the critical strain of void nucleation was greater in the LBW-welded joints than in the TIG-welded joints, while the growth rate of voids was lower in the LBW-welded joints than in the TIG-welded joints. Thus, the damage ratio in the LBW joints was lower than that in the TIG-welded joints during tensile testing. This can be due to the coarser martensitic α′ and the application of TC-1 welding rods in the TIG-welded joint.

Microstructure and Mechanical Properties of TWIP Steel Joints

As a new type of high manganese steel, the twinning induced plasticity (TWIP) steels have attracted a growing interest in the automotive industry due to their good performance. Thin plates of TWIP steel were welded by laser beam welding (LBW) and gas tungsten arc welding (GTAW). The microstructure result shows that GTAW joint has obvious heat-affected zone (HAZ), while the HAZ of LBW joint is almost invisible. The X-ray diffraction result shows that the phase compositions of both joints arc austenitic and no phase transition occurs. Energy dispersive spectrometry result shows that there is violent evaporation of Mn element in LBW joint, while the proportion of Mn element in GTAW joint is almost unchanged. Tensile tests and micro-hardness measurements were performed to take into account the mechanical properties of joints manufactured by the two different processes. The micro-hardness profiles of both joints present a typical saddle distribution, and the hardness of GTAW scam is lower than that of LBW scam. The failure positions of LBW joints arc all located in base metal while the GTAW joints arc all at the weld toe due to the softening of HAZ. By means of scanning electron microscopy, a typical ductile fracture is observed in LBW joint, while a brittle fracture with quasi-cleavage fracture characteristic is observed in GTAW joint.

Multiaxial fatigue evaluation of laserbeam-welded magnesium joints according to IIW-fatigue design recommendations

Under non-proportional multiaxial loading, welded magnesium joints show a decrease of fatigue life compared to combined proportional loading as is also observed for welded ductile steels and aluminium alloys. The investigated laserbeam-welded overlapped tube-tube joints of the wrought magnesium alloys AZ31 and AZ61 were tested under combined in- and out-of-phase axial loading and torsion. The IIW-Recommendations for the evaluation of multiaxial stress states with constant and with changing principal stress directions describe, on the safe side, the results obtained for fully reversed loading R = −1 and the probability of survival P s = 50 %. The comparisons of the experimental results with the allowable values for P s = 97.7 % and R = 0.5 are quite conservative. However, as, at present, relatively few multiaxial fatigue investigations with magnesium alloys in the welded state are available, the suggested IIW procedure, the Gough-Pollard Equation with the multiaxial damage parameters D MA = 1.0 and 0.5, should be retained.

On the Use of Infrared Thermography for Analysis of Fatigue Damage in Ti6Al4V-Welded Joints

The present work is aimed at comparatively studying fatigue damage evolution of a pulsed Nd:YAG laser beam-welded (LBW) joint and the base metal (BM) of Ti6Al4V alloy subjected to cyclic loading. To reveal crack nucleation and propagation during the fatigue process, in situ fatigue was generated using infrared measurement methods. The results indicate that the rate of damage accumulated in the LBW joint was higher than in the BM specimens during a fatigue test, which decreased the fatigue life of the LBW joint. This observation is attributable to the LBW joint fusion zone microstructure, which has a higher void nucleation and growth rate compared with the BM microstructure.

Gas tungsten arc and laser beam welding processes effects on duplex stainless steel 2205 properties

► LBW results in considerable variation in the ferrite–austenite balance of FZ. ► LBW produces smaller FZ size than GTAW. ► The effect of FZ size is more pronounced than that of ferrite–austenite balance. ► Satisfactory mechanical properties were obtained using both GTAW and LBW. ► LBW process has produced welded joint properties comparable to BM. A comparative study on the influence of gas tungsten arc welding (GTAW) and carbon dioxide laser beam welding (LBW) processes on the size and microstructure of fusion zone FZ then, on the mechanical and corrosion properties of duplex stainless steel DSS grade 2205 plates of 6.4 mm thickness was investigated. Autogenous butt welded joints were made using both GTAW and LBW. The GTA welded joint was made using well established welding parameters (i.e., current ampere of 110 A, voltage of 12 V, welding speed of 0.15 m/min and argon shielding rate of 15 l/min). While optimum LBW parameters were used (i.e., welding speed of 0.5 m/min, defocusing distance of 0.0 mm, argon shielding flow rate of 20 l/min and maximum output laser power of 8 kW). The results achieved in this investigation disclose that welding process play an important role in obtaining satisfactory weld properties. In comparison with GTAW, LBW has produced welded joint with a significant decrease in FZ size and acceptable weld profile. The ferrite–austenite balance of both weld metal WM and heat affected zone (HAZ) are influenced by heat input which is a function of welding process. In comparison with LBW, GTAW has resulted in ferrite–austenite balance close to that of base metal BM due to higher heat input in GTAW. However, properties of LB welded joint, particularly corrosion resistance are much better than that of GTA welded joint. The measured corrosion rates for LBW and GTAW joints are 0.05334 mm/year and 0.2456 mm/year, respectively. This is related to the relatively small size of both WM and HAZ produced in the case of LBW. In other words, properties of welded joints are remarkably influenced by FZ size rather than the produced austenite–ferrite balance.

Study on microstructure and mechanical properties of Al–Mg–Mn–Er alloy joints welded by TIG and laser beam

Al-4.7Mg-0.7Mn-0.3Er alloy plates were welded by laser beam welding (LBW) and tungsten inert gas (TIG). Mechanical properties and microstructures of both welded joints were analyzed. The results showed that the tensile strength of LBW joint was 315MPa, which was approximately 10% higher than that of TIG welded joint. This was attributed to the fine grains, dispersed primary Al3Er phase and low Mg evaporation in LBW weld. Equiaxed grains with average size of 30μm were obtained in the fusion zone, which were much smaller than that of 90μm in the fusion zone of TIG joint, due to the low heat input during LBW process. Moreover, finer primary Al3Er particles were uniformly distributed in the LBW joints, which resulted in a substantial increase of nucleation rate in LBW welds. In addition, it was also found that Mg concentrations in the fusion zones, in both TIG and LBW joints, were lower than that of the base one tested by EPMA. The burning loss rates of Mg in TIG and LBW joints were 36% and 22%, respectively.

CO2 laser welding of interstitial free galvanized steel sheets used in tailor welded blanks

Recently, laser welding technologies have been widely utilized to weld different automobile panels. In this research, the laser beam welding (LBW) process of interstitial free (IF) steel sheets used in the manufacturing of the car body was investigated on the basis of mathematical models. The quality indexes of LBW joints were estimated from Erichsen Cupping Test results including strength and Erichsen Cupping Index. Furthermore, three process parameters, namely laser power (P), welding speed (S), and focal position (F) were considered as the factors influencing the quality indexes. A 2.2-kW CO2-laser beam was utilized to weld 1.2- and 0.8-mm-thick IF steel sheets. The modeling is done using experimental data which were gathered using design of experiments approach based on central composite face centered design matrix. The final regression models can be used to predict the quality indexes of laser beam-welded IF steel sheets joints at 95% confidence level. Optical metallography was utilized to characterize the weld profile and microstructures. In the second phase of this research, multi-objective genetic algorithm with the fitness function based on regression models was employed as an optimization procedure; as a result, the best quality indexes were obtained. Optimization results showed high compatibility with the actual experimental data.

Fatigue assessment of laserbeam‐welded aluminium joints under multiaxial loading

AbstractThis paper presents the results and evaluation of the multiaxial fatigue behaviour of laserbeam‐welded overlapped tubular joints made from the artificially hardened aluminium alloy AlSi1MgMn T6 (EN AW 6082 T6) under multiaxial loadings with constant and variable amplitudes. Several fatigue test series under pure axial and pure torsional loadings as well as combined axial and torsional proportional and non‐proportional loadings have been carried out in the range of 2·104 to 2·107 cycles. The assessment of the investigated thin‐walled joints is based on a local notch stress concept. In this concept the fatigue critical area of the weld root is substituted by a fictitious notch radius rref = 0.05 mm. The equivalent stresses in the notch, considering especially the fatigue life reducing influence of non‐proportional loading in comparison to proportional loading, were calculated by a recently developed hypothesis, which is called the Stress Space Curve Hypothesis (SSCH). This hypothesis is based on the time evolution of the stress state during one load cycle. In addition, the fatigue strength evaluation of multiaxial spectrum loading was carried out using a modified Gough‐Pollard algorithm.

Influence of welding processes on microstructure, tensile and impact properties of Ti-6Al-4V alloy joints

Titanium alloys have been successfully applied for aerospace, ship and chemical industries because they possess many good characteristics such as high specific strength, superior corrosion resistance and excellent high temperature resistance. Though these alloys show reasonable weldability characteristics, the joint properties are greatly influenced by the welding processes. Weld thermal cycle of the processes will control the weld metal solidification and subsequent phase transformation and resultant microstructure. The welded joints of Ti-6Al-4V alloy were fabricated by gas tungsten arc welding (GTAW), laser beam welding (LBW) and electron beam welding (EBW) processes. The joints fabricated by EBW process exhibit higher strength compared with the GTAW and LBW joints; but the joints by GTAW process exhibit higher impact toughness compared with the LBW and EBW joints. The resultant tensile and impact properties of the welded joints were correlated with the weld metal microstructures.

Metallurgical characterization of pulsed current gas tungsten arc, friction stir and laser beam welded AZ31B magnesium alloy joints

This paper reports the influences of welding processes such as friction stir welding (FSW), laser beam welding (LBW) and pulsed current gas tungsten arc welding (PCGTAW) on mechanical and metallurgical properties of AZ31B magnesium alloy. Optical microscopy, scanning electron microscopy, transmission electron microscopy and X-Ray diffraction technique were used to evaluate the metallurgical characteristics of welded joints. LBW joints exhibited superior tensile properties compared to FSW and PCGTAW joints due to the formation of finer grains in weld region, higher fusion zone hardness, the absence of heat affected zone, presence of uniformly distributed finer precipitates in weld region.

Fatigue of Laserbeam Welded Joints of High-Carbon Steel Strips

The high-carbon steel strips are one of the most widely used base materials of bandsaw blade manufacturing. These materials have sufficient strength and ductility to cope with the high fatigue load of the bandsaw blades. These endless strips are produced by welding, and therefore the weld and the heat affected zone have different mechanical properties, like tensile strength and fatigue resistance, than the base material. These properties of the weld can be influenced by preheat and post weld heat treatment. Regarding to the latest industrial requirements, the application of laserbeam welding was examined to produce higher standard bandsaw blade. The laserbeam welded joints has lower heat input and narrower heat affected zone compared to metal inert gas (MIG) welding, which is currently used in bandsaw blade manufacturing. To assure the proper mechanical properties and sufficient resistance to fatigue, an examination was carried out to determine the effect of preheat temperature and post weld heat treatment time on the mechanical properties and fatigue behaviour of the laserbeam welded joint.