Laser Welding Of Aluminum Alloys Research Articles

Local zone-wise elastic-plastic constitutive parameters of Laser-welded aluminium alloy 6061 using digital image correlation

The mechanical properties of aluminium alloys can be affected by the local high temperature in laser welding. In this paper, an inversion identification method of local zone-wise elastic-plastic constitutive parameters for laser welding of aluminium alloy 6061 was proposed based on full-field optical measurement data using digital image correlation (DIC). Three regions, i.e., the fusion zone, heat-affected zone, and base zone, of the laser-welded joint were distinguished by means of microstructure optical observation and micrometer hardness measurement. The stress data were obtained using a laser-welded specimen via a uniaxial tensile test. Meanwhile, the local strain data of the laser-welded specimen were obtained by the DIC technique. Thus, the stress–strain relationship for different local regions was established. Finally, the constitutive parameters of the Ramberg–Osgood model were identified by least-square fitting to the experimental stress–strain data. Experimental results revealed that the mechanical properties of the local zones of the welded joints clearly weakened, and these results are consistent with the results of the hardness measurement.

The Effect of Process Parameters on the Microstructure and Mechanical Performance of Fiber Laser-Welded AA5182 Aluminium Alloys

The laser welding of aluminium alloys is an important industrial technology but many challenges remain. The objective of this research is to investigate the effect of laser welding parameters on the quality of the fiber laser lap welded AA5182 aluminium alloy. The influences of the laser power, welding speed and focal point position on the mechanical and microhardness properties of the joints were experimentally investigated. The mechanical properties of the joints were evaluated by performing tensile tests. From the experimental results, optimum process parameters were determined, and microstructural examination and microhardness tests were conducted to better understand the performance of the joints. It was found that there is a correlation between the tensile shear loads of the joints and heat input per unit length. At the optimized parameters, the welded joint showed good weld appearance without macro defects, and the joint had an adequate tensile shear load.

Identification of Constitutive Parameters of Laser Welded Aluminum Alloy Using Digital Image Correlation

An inversion identification method of local wise elastic-plastic constitutive parameters for laser welding of aluminum alloys 6061 was proposed based on full-field optical measurement data using digital image correlation (DIC). Three regions, fusion zone, heat affected zone and base zone of the laser welded joint were distinguished by means of microstructure optical observation and micrometer hardness measurement. The stress data was obtained by the laser welded specimen under uniaxial tensile test, meanwhile, the local strain data of the laser welded specimen was measured by the DIC technique, so the stress-strain relationship for different local regions was established. At last, the constitutive parameters of Ramberg-Osgood model were identified by least-square fitting to the experimental stress-strain data. Experimental results reveal that the mechanical properties for the local zones of welded joint are obviously weakened, which are consistent with the hardness measurement.

Effect of ambient pressure on interaction between laser radiation and plasma plume in fiber laser welding

Fiber laser welding of aluminum alloy under vacuum was performed in this study. To understand the increases in weld penetration depth and changes in weld cross section profile in laser welding under vacuum or subatmospheric pressure, the effect of ambient pressure on interaction between laser radiation and plasma plume was studied. The electron temperature, electron density and inverse bremsstrahlung absorption of laser energy were calculated by spectroscopic analyses. The attenuation and refraction of laser energy from plasma plume were studied by probe laser beam measurements. It was found that the inverse bremsstrahlung absorption, attenuation and refraction of laser energy were sensitive to ambient pressure and decreased with the decrease of ambient pressure. Based on the effect of ambient pressure on boiling temperature of materials and interaction between laser radiation and plasma plume, the laser energy absorption mechanisms between atmosphere and vacuum was compared. The finding suggested that the decreasing of plasma plume disturbance, the increasing of the laser energy in keyhole and the decreasing of boiling temperature changed the absorption mechanism of laser energy, resulting in a large aspect ratio with narrow and parallel sides of weld cross section profile under vacuum.

Factors controlling keyhole-induced porosity in cold wire laser welded aluminum

Production of lightweight laser-welded assemblies to meet the requirements for higher performance and reduction of carbon emission requires substantial effort in mitigating the effects of processing on welding defects. The factors controlling keyhole-induced porosity during cold wire laser welding of AA6061-T6 were studied. The laser beam intensity distribution parameters and the laser energy deposited per unit length of the weld determine the keyhole behavior, the shape and size of the surrounding molten material and, consequently, the percentage of porosity and average size of pores that resulted from keyhole collapse during welding. Changes in keyhole size and porosity are not noticeably significant with respect to the rate of feeding the cold wire into the molten weld pool. The vapor plume that forms above the molten pool due to the ejection of evaporated metal particles from the keyhole effectively attenuates the laser beam and reduces the depth of penetration. However, the erratic behavior of the plume results in an inconsistent porosity response. The use of a gas jet for deflecting the plume is beneficial for more consistent porosity response. Results from this work provide guiding principles for the selection of process variables for keyhole-mode laser welding of aluminum alloys, depending on the particular application and the criteria for acceptable level of defects.

Hybrid laser-arc welding of aluminium alloys

Special features of laser welding of aluminium alloys with laser and arc heat sources are investigated. Advantages and shortcomings of these methods are noted. Experiments were carried out to combine laser and arc heat sources for welding aluminium alloys. Equipment for hybrid welding is described. The technological parameters influencing the external formation of the welded joints are determined. Specific conditions for welding 1424 aluminium alloys with a thickness of 4.0 mm are presented. High-quality welded joints were produced by hybrid laser-arc welding in 1424 alloy with a thickness of 4.0 mm.

Study on the burning loss of magnesium in fiber laser welding of an Al-Mg alloy by optical emission spectroscopy

In order to study the burning loss of magnesium, a specially designed device was used to capture the spectrum emitted from the keyhole plasma in deep penetration laser welding of aluminum alloy 5052. The content of magnesium in the weld bead was measured by an electron probe micro-analyzer (EPMA). The effect of the welding parameters on the spectral intensity of magnesium plasma was examined, and the distributions of the spectral intensity of magnesium plasma in the radial and depth directions of the keyhole were investigated. Finally, the mechanism of the magnesium loss was analyzed. The results indicate that burning loss of magnesium can be monitored by spectral analysis technique. The welding parameters have a great effect on the burning loss of magnesium. The influence of welding speed on the burning loss of magnesium on the top surface is dependent on the penetration regime. The distribution of magnesium in the weld is not uniform. In the radial direction of the weld bead, the content of magnesium increases from the center to the edge of the keyhole. In the depth direction of the weld bead, the content of magnesium decreases firstly and then increases from the top to bottom. The maximum burning loss of magnesium occurs at the middle of the weld bead.

Trend and innovations in laser beam welding of wrought aluminum alloys

The drive toward fulfilling weight reduction obligation, superior weld quality requirement, and industrial manufacturing rationale has sprung up considerable interest in applying laser welding technology on aluminum alloys. Nevertheless, porosity, solidification cracking, and surface reflectivity have been the major banes of laser welding of aluminum alloys. However, literature has shown that positive efforts have been accomplished in reducing these fundamental concerns by adopting careful selection of welding procedure, modification of pure laser welding techniques, and the use of appropriate filler metal. Albeit, there is still upbeat progression on the application and improvement of laser welding of aluminum alloys. At present, laser welding technology has the potential of fulfilling industrial requirements in joining lightweight aluminum alloys because of its capacity for automation and intrinsic flexibility, precision and repeatability, low general heat input, high welding speed, and low weld distortion. As a result, this report examines the available and current status of laser technologies in welding aluminum alloys. It further categorizes the laser technologies of aluminum alloys into four assemblages, namely, pure or single-beam laser welding, laser-arc hybrid welding, tailored heat source laser welding, and other innovative laser welding technologies, respectively. Mechanical, corrosion, and microstructural behaviors of laser welded aluminum alloys are also studied. Conversely, some of the research areas that need further investigations are proposed. Corrosion behavioral properties, influence of micropores on fatigue and quasi-static tensile strength, and toughness characterization of laser welded aluminum alloys are insufficient in literature.

High-Speed X-Ray Transmission and Numerical Study of Melt Flows inside the Molten Pool during Laser Welding of Aluminum Alloy

By using the X-ray transmission imaging system, melt flows inside a molten pool were studied during laser welding of aluminum alloy at different welding speeds. Then, the correlation between temperature gradients along the direction of weld penetration and melt flows in the rear part of a molten pool was analyzed by using a three-dimensional numerical method. And the presented model was verified by experimental results. The corresponding investigation was carried out to further study the correlation between temperature gradient and melt flow behavior of the molten pool in the plate heated by preheating temperature. The results indicated that, in the rear part of the molten pool, the maximum flow velocity was located at the bottom of the molten pool. The melt metal in the rear molten pool caused by different welding speeds had significantly different flow trends. As the welding speed increased, the absorbed intensity on the keyhole front wall also increased as well as the recoil pressure that could maintain the keyhole opened. Consequently, the increase of the welding speed was more beneficial to improving the stability of the molten pool.

Investigation of the technology of laser welding of aluminum alloy 1424

In this study, certain technological variants of the laser welding of alloy 1424 of the Al–Mg–Li–Zr system are considered with the purpose of obtaining the durability level of the welded joint, which is close to that of the basic metal. It is shown that, in the case of using various types of plastic deformation of the welded joint, its durability can be increased considerably to 0.85–0.95 from that of the basic metal.

Modeling of butt and lap joint laser welding of aluminum alloys and constructional steel sheets

Modeling of butt and lap joint laser welding of aluminum alloys and constructional steel sheets

Aluminum welding by combining a diode laser with a pulsed Nd:YAG laser

Laser welding of aluminum alloys (AA 5754 and AA 6016) by superimposing a pulsed Nd:YAG laser with a continuous wave (cw) diode laser has been investigated in order to improve the weldability and the process efficiency. The low absorption of laser radiation at a wavelength of 1064 nm and the high thermal conductivity make it difficult to laser weld aluminum alloys efficiently. Therefore, a pulsed Nd:YAG laser and a low power diode laser emitting a wavelength of 980 nm were spatially superimposed. This configuration allows to enhance the absorption for the Nd:YAG welding laser due to the preheating of the diode laser. Thus, the process efficiency as well as the weld quality is enhanced. The experiments revealed that a small output power of the diode laser (<150 W) allows increasing the welding speed up to 80 % and the weld depth up to 38 %. Furthermore, the superposition leads to a significant improve of the weld seam quality, in particular to avoid hot cracking.

Experimental and numerical analysis of solidification cracking behaviour in fibre laser welding of 6013 aluminium alloy

Experimental observation and numerical modelling were employed to investigate the solidification cracking behaviour during fibre laser welding of 6013 aluminium alloy. The solidification cracking initiation location and propagation path were studied using a high speed camera system and via metallurgical analysis. A three-dimensional thermomechanical finite element model of fibre laser welding of aluminium alloys was developed, which considered cylindrical volumetric heat source, temperature dependent material properties, solidification shrinkage and stress relaxation in the weld molten pool. The transient evolution and distribution of mechanical strain in the brittle temperature range (BTR) were analysed in detail to find the factors which drove the crack initiation and propagation. The results showed that the solidification cracking initiated near the fusion line and then propagated along the centreline of the weld, which was the result of the strain distribution characteristic in BTR.

Characteristics of plasma plume in fiber laser welding of aluminum alloy

To understand the laser–matter interaction in fiber laser welding of aluminum alloys, the effects of laser power on the characteristics of fiber laser induced plasma plume were studied by emission spectroscopic analysis firstly. The plasma characteristic parameters including electron temperature, electron density, ionization degree, and inverse bremsstrahlung linear absorption coefficient were computed according to the spectral data. It was found that the laser power of 5kW is a turning point. After the laser power reaches 5kW, the plume changes from a metal vapor dominated weakly ionized plasma to a strongly ionized plasma. The corresponding phenomena are the dramatic increase of the value of characteristic parameters and the appearance of strong plasma shielding effect. The calculation of effective laser power density demonstrated that the plasma shielding effect is dominated by inverse bremsstrahlung absorption. The finding suggested the plasma shielding effect must be considered in fiber laser welding of aluminum alloys, rather than is ignored as claimed in previous view.

Mechanical constraint intensity effects on solidification cracking during laser welding of aluminum alloys

Effects of mechanical constraint intensity on solidification cracking behavior were investigated in single-side and double-side constraint conditions, respectively. A numerical model was developed to simulate the solidification cracking behavior during the laser welding process. The mechanical strain and accumulated crack-tip displacement were adopted to analyze the susceptibility of crack initiation and propagation, respectively. Results show that crack behavior is greatly influenced by mechanical constraint intensity. Stronger constraint intensity promotes the initiation of crack for both single-side and double-side constraint conditions. Higher constraint intensity tends to promote crack propagation in single-side constraint condition, and helps to suppress crack propagation in double-side constraint condition.

Self-consistent modeling of keyhole and weld pool dynamics in tandem dual beam laser welding of aluminum alloy

A three dimensional model incorporating heat transfer, fluid flow and the keyhole free surface, Marangoni force, surface tension and recoil pressure is described. Possible multiple reflection Fresnel absorptions in complex keyhole profiles and laser plume interactions are also treated in the model. The results show that the keyhole is usually highly unstable and its depth undergoes severe oscillations in deep penetration tandem dual beam laser welding. The frequency of the depth oscillations is several kHz, which is comparable to that in single beam laser welding. Under the same heat input conditions, the amplitude of keyhole depth oscillations is smaller than that in single beam laser welding. Increasing the welding speed could improve the keyhole instability in dual beam laser welding. The mechanism of process stabilization of tandem dual beam laser welding over single beam laser welding is a joint effect of several beneficial physical factors, but not only the common known degassing effect. Good agreement is obtained between simulation results and prior experiments.

Prediction of solidification cracking in pulsed laser welding of 2024 aluminum alloy

Laser welding of aluminum alloys can be associated with solidification cracking. The severity of cracking in these alloys depends on various factors, such as the initial temperature of the base metal and the temporal amplitude of the laser pulse. The purpose of this investigation is to understand this correlation, and thus to put forward a criterion for solidification cracking in laser welding of 2024 aluminum alloy. The criterion for cracking is devised based on a modification of the existing criteria, to account for non-steady conditions, and interpreted with respect to the loci of the relevant isotherms and the length of the vulnerable zone in the melt pool, during the solidification stage. Based on this criterion and the respective experimental observations, it is demonstrated that welding with suitable ramping down of the laser pulse can lead to the elimination of solidification cracking in the examined alloy.

Influence of Temperature Profile during Laser Welding of Aluminum Alloy 6061 T6 on Microstructure and Mechanical Properties

In the present study, laser welding was carried out with CO2 laser on a 2 mm thick aluminum alloy (6061-T6) sheet to study laser weldability of this heat-treatable aluminum alloy. Screening experiments were performed initially to enumerate the power density requirement for proper coupling of the laser with the material. Bead on plate experiments were conducted to recognize situation under which stable keyhole and welds with minimum defects (porosity and cracks) can be produced. Recognized process window (3 kW power, 4 m/min welding speed, and 18 L/min Helium flow rate) obtained from initial trial was used in butt welding experiment and the resulted weld was characterized by macroscopic and microscopic observation, microhardness study, and tensile test. The microstructure reveals porosity and crack-free welds and hardness data confirmed presence of heat-affected zone (HAZ) and huge drop in overall hardness after welding. After post-weld treatment (aging treatment), the hardness was increased marginally, but base hardness could not be achieved. Thermal profile experienced by the material during welding was calculated and it revealed that the mechanical properties of the material decreased due to temperature experienced by the material lead to loss of aging properties of the material.

The effects of short pulse laser surface cleaning on porosity formation and reduction in laser welding of aluminium alloy for automotive component manufacture

Laser welding of aluminium alloys typically results in porosity in the fusion zones, leading to poor mechanical and corrosion performances. Mechanical and chemical cleaning of surfaces has been used previously to remove contaminants for weld joint preparations. However, these methods are slow, ineffective (e.g. due to hydrogen trapping) or lead to environmental hazards. This paper reports the effects of short pulsed laser surface cleaning on porosity formation and reduction in laser welding of AC-170PX (AA6014) aluminium sheets (coated with Ti/Zr and lubricated using a dry lubricant AlO70) with two types of joints: fillet edge and flange couch, using an AA4043 filler wire for automotive component assembly. The effect of laser cleaning on porosity reduction during laser welding using a filler wire has not been reported before. In this work, porosity and weld fusion zone geometry were examined prior to and after laser cleaning. The nanosecond pulsed Nd:YAG laser cleaning was found to reduce porosity significantly in the weld fusion zones. For the fillet edge welds, porosity was reduced to less than 0.5% compared with 10–80% without laser cleaning. For flange couch welds, porosity was reduced to 0.23–0.8% with laser cleaning from 0.7% to 4.3% without laser cleaning. This has been found to be due to the elimination of contaminations and oxide layers that contribute to the porosity formation. The laser cleaning is based on thermal ablation.

Analysis of solidification cracking susceptibility in side-by-side dual-beam laser welding of aluminum alloys

In this paper, an experimental study combined with a numerical model consideration of both thermal conduction and fluid flow in the molten pool were carried out, aiming to analyze solidification cracking susceptibility of dual-beam laser welding on Al alloys. The maximum accumulated transverse displacement in the mushy zone was calculated based on the strip expansion technique and employed to evaluate centerline solidification cracking susceptibility. Numerical calculations showed that increasing inter-beam spacing in side-by-side dual-beam laser welding of Al alloys could lead to increased accumulated transverse displacement in the weld, resulting in higher solidification cracking susceptibility, which agreed well with experimental observations. The analysis results also showed that increasing the laser power or reducing the welding velocity increased hot cracking susceptibility. The optimum cracking-free welding condition for dual-beam laser welding of Al can be determined with the help of numerical modeling, in which the hot cracking susceptibility can be evaluated and numerically reduced by adjusting welding process variables.