Laser Welding Of Aluminum Research Articles

Mechanical and microstructural characterization of laser-welded joints of 6013-T4 aluminum alloy

Laser beam welding may be used in the place of the traditional riveting process for the welding of the stringers to the skin in aircrafts. This work intends to investigate the mechanical behavior of laser-welded aluminum AA6013, subjected to post-welding heating treatments (PWHT). A fiber laser with an average power of 1.5 kW was used to weld two 1.6-mm-thick sheets in T-joint configuration. After welding, the samples were separated in three groups: the first just welded, the second subjected to a PWHT during 4 h at 190 °C and the third during 2 h at 205 °C. Hoop tensile tests showed that the thermal treatment at 190 °C for 4 h increased the tensile strength in 76 MPa, but the strain had decreased 4 %; the thermal treatment at 205 °C for 2 h increased maximum strength in 65 MPa, with a decrease in strain of 5 %. In T-pull tensile tests, the tensile properties of as-welded and PWHT samples remained the same. Standard S–N curve showed that the welding reduce the number of cycles to failure for the tested stairs. PWHT did not affect fatigue properties.

Influence of grain refinement on hot cracking in laser welding of aluminum

Hot cracking is a major problem in casting and laser welding of important technical aluminum alloys. A well-known method to reduce this problem is grain refinement. The mechanism of hot cracking prevention by grain refinement is not fully understood yet. In this study, different amounts of titanium and boron were added into weld in laser welding of AA 6082, which lead to different grain structures. A hot cracking test (DELTA test) was carried out to investigate the influence of grain refinement on hot cracking susceptibility of the welds. In order to understand the mechanism of hot cracking prevention by grain refinement, an analytical model was developed, which describes the influences of the grain structure and solidifications parameter on the three following factors, the duration of the mush zone, the capillary pressure for hot cracking, as well as the permeability of the dendritic network in the molten pool. It reveals that the hot cracking susceptibility is determined by the combination effect of these three factors. There is an optimum grain size for a minimal hot cracking susceptibility. It agrees with the experimental results in DELTA test.

Performance enhancement of aluminum infrared laser welding by preconditioning with nanosecond laser pulses

We condition the welding zone of the aluminum surface with nanosecond laser pulses prior to welding with infrared laser radiation to increase the process efficiency and weld quality. The high reflectivity of aluminum for infrared laser radiation (95% at 1064 nm) leads to poor process efficiency of aluminum laser welding processes. To increase the workpiece's absorptivity, the welding zone is conditioned with nanosecond laser pulses at a wavelength of 532 nm. The samples are nonalloy, 0.5 mm thick aluminum, and 1.5 mm thick Al5356 alloy. Welding is performed with a continuous Nd: yttrium aluminum garnet (YAG) laser with an output power of 2 kW, a pulsed Nd:YAG laser with an average power of up to 90 W, and a pulsed Nd:YAG laser with an average power of up to 20 W. Through preconditioning with nanosecond laser pulses, full penetration welding is achieved with an increased welding speed. At the same welding speed, the bead size of the weld increases and deeper penetration of bead on plate welding is obtained. The authors observe higher surface oxygen content of the preconditioned aluminum surface which is expected to increase the absorptivity. Pore formation is reduced when employing the preconditioning on the Al5356 alloy.

Non-destructive Testing of Porosity in Laser Welded Aluminium Alloy Plates: Laser Ultrasound and Frequency-Bandwidth Analysis

Embedded welding defects, such as porosities and cracks, are generally formed during aluminium laser welding. It is challenging to test these defects with current non-destructive evaluation (NDE) methods. This work features the creation of defects and their study with the help of NDE methods. The chosen method should be able to detect porosities in lap-welded sheets of 5754 aluminium alloys.

Effects of Diode Laser Superposition on Pulsed Laser Welding of Aluminum

Abstract Pulsed laser welding of thin aluminum sheets is common for housing, where welding defects are detrimental especially in terms of hermetic packaging as well as electromagnetic compatibility. This paper shows investigations on laser welding of aluminum by superposition of a pulsed Nd:YAG laser with a diode laser in order to improve the weldability of aluminum. This configuration allows to enhance the absorption of the Nd:YAG welding laser due to preheating by the diode laser. Furthermore the effects of temporal pulse shaping have been studied experimentally. Deeper penetrations as well as an increased weld quality in terms of cracking were observed in welds manufactured with diode laser superposition. Besides this the modification of the thermal cycle by the combination of the two laser beams promotes advantageous solidification conditions and therefore hot cracks were efficiently reduced or avoided. Additionally solidification conditions can be actively influenced. The results show a decreasing number of defects and additionally an increase of the welding quality.

Remote Laser Welding of Multi-Alloy Aluminum at Close-Edge Position

6000 series (magnesium and silicon based) aluminum alloys are highly susceptible to hot cracking during laser beam welding. The occurrence of hot cracks depends on thermo-mechanical strain at the solidifying stage of the melt and in the micro-scale on the solidification structure. A new metallurgical approach to avoid these cracks by affecting the solidification process is using a multi-alloy aluminum with a silicon-rich layer. Within this paper infrared videos were used to investigate and compare the behavior of this new material with the 6xxx monolithic alloy at hot crack sensitive close-edge positions.

铝/钢异种材料激光焊接现状与展望

铝/钢异种材料激光焊接现状与展望

铝/钢异种材料激光焊接现状与展望

铝/钢异种材料激光焊接现状与展望

Control of aluminium laser welding conditions with the help of numerical modelling

Numerical modelling of laser welding in both conduction and keyhole modes is studied to highlight the influence of the main welding parameters on assembly performance.Numerical simulation enables the thermal history of assembly weld joints to be described. A hot cracking criterion is proposed. The model predicts that (1) a deviation in the localization of the shielding gas does not affect instability and that (2) fluctuations of the absorbed laser beam power generate cooling speed deviations. The results also demonstrate that laser welding in keyhole mode, when compared to laser welding in conduction mode, is more likely to induce higher cooling speeds, greater risks of hot cracking but better sensitivity to post weld age hardening heat treatment.

Overlap conduction laser welding of aluminium to steel

In the present study, a continuous wave fibre laser was used in conduction mode to join aluminium alloys to low carbon steel. Two different sets of experiments were performed: with Zn-coated steel and uncoated steel. Welding was carried out in overlap configuration with steel plate on the top aiming to conduct the heat through the steel and melt the aluminium at the interface, wetting the steel substrate. Metallurgical incompatibilities between these two participating alloys originate the formation of intermetallic phases. Therefore, restricting melting of the aluminium would limit the formation and growth of the intermetallic layer (IML). It was shown that the power density of the laser could be used such that, at the interface, aluminium only melts and the steel remains in solid state. The uncoated steel showed a regular pattern of IML formation, while the Zn-coated steel showed a different pattern of IML.

Optimization of Laser Welding Parameters in Aluminum Alloy Welding and Development of Quality Monitoring System for Light Weight Vehicle

In this paper laser welding AA5182 of aluminum alloy with AA5356 filler wire were performed with respect to laser power, welding speed, and wire feed rate. The experiments showed that the tensile strength of the weld was higher than that of the base material under sufficient heat input conditions. A genetic algorithm was used to optimize process parameters which were the laser power, welding speed, and wire feed rate. To do that, a fitness function was formulated, taking into account weldability and productivity. A factor for the weldabilty used tensile strength estimation model which was made by neural network, and as the productivity, welding speed, and wire feed rate were used. Weld monitoring system for aluminum laser welding with filler wire was constructed through the optical sensors to measure the plasma light intensity. Relationship between monitoring signal and plasma and keyhole behavior according to welding condition was analyzed and it was found that sensor signal could express the information for weld quality. Weld quality estimation algorithm was formulated fuzzy multi feature pattern recognition algorithm using the monitoring signals. Quality prediction system was also developed to apply this algorithm to production line.

Study on Solidification Crack Criterion during Laser Welding Pure Aluminum and ZL114A Aluminum Alloy

Laser welding of 1A90 pure aluminum and ZL114A aluminum alloy with powder under the same laser welding parameters were carried out in this work. The relation between weld elements and solidification cracking formation of these two materials was investigated in the perspective of metallurgical factor. And the alloy element contents and distribution near the cracks were determined by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). Then the concept of weld element equivalent was introduced comparing with the carbon equivalent expression. The weld element equivalent expressions were established by using mathematics regress. And the verified results indicate that the weld element equivalent expressions can properly forecast the formation of solidification cracking.

Porosity in fiber laser formation of 5A06 aluminum alloy

The mechanism of porosity formation and its suppression methods in laser formation of aluminum alloy have been studied using a 4kW fiber laser to weld 5A06 aluminum alloy with SAl-Mg5 filler. It was found that the porosity formation is closely related to the stability of the keyhole and fluctuation of the molten pool in the laser welding aluminum alloy. The filling wire increased the instability of the keyhole and weld pool, thus further increasing the amount of gas cavities in the joint. Prefabrication of a suitable gap for the butt joint can provide a natural passage for the flow of the liquid metal, which can weaken, and even completely eliminate the disturbance of the filling wire on the formation of keyhole. The gap can also provide a passage for the escape of the bubble. Thus, this method can greatly decrease the sheet’s susceptibility to porosity. Moreover, for a thin sheet, if the power of the laser is sufficient to form a keyhole with stable penetration through the weld sheet, a weld bead without porosity can also be obtained because closing the keyhole is almost impossible.

Inherent instability investigation for low speed laser welding of aluminum using a single-mode fiber laser

The causes of instability are investigated for low speed welding of aluminum from 10 mm/s down to 1 mm/s using a 300 W single-mode fiber laser. Results show that the welding is stable until the speed drops below a certain threshold (∼1 mm/s) at which there was a significant change in the process mechanism, causing shallow, inefficient welds with many defects. A power distribution model and several tests are used to examine different types of power losses at low speeds. It is then hypothesized that, at low speeds, the CW laser beam mainly irradiates at the molten pool, which absorbs a large portion of the beam energy near the surface. The majority of this absorbed energy subsequently is either lost via evaporation or transferred into the bulk material via convection and conduction without being used for melting the solid at the welding front. A laser pulsing scheme was used to test the above hypothesis. It was found that, through proper control of the duty cycle and frequency to prevent overheating of the molten pool, a high aspect ratio weld shape can be restored at low speeds, thus, confirming the hypothesis. In addition, the 1 mm/s low speed threshold is found to be related to the initial molten pool propagation speed, which is found to be approximately 1.4 mm/s. Although this paper does not propose a solution to restore process stability, the understanding of the instability origin will be helpful in the search of such a solution to overcome the process instability for slow speed welding of aluminum.

Simulation of plasma dynamics in a keyhole during laser welding of metal with deep penetration

Physical processes occurring in the keyhole during the deep-penetration laser welding of aluminium, where evaporation, ionization and formation of near-surface low-temperature plasma can take place, are studied theoretically. Equations of radiation gas dynamics including the equilibrium model of plasma, description of laser radiation transport and absorption are solved. Numerical calculations of plasma cloud propagation processes in aluminium vapour are performed in a one-dimensional approach. The minimum radiation power necessary to maintain this cloud is found. The effect of radiation trapping by plasma due to self-absorption in the optically thick plasma layer is revealed. The simulation results are of interest for a qualitative understanding of the processes in the keyhole plasma.

Welding of Aluminum Using a Pulsed Nd:YAG Laser

This paper deals with pulsed laser welding of aluminum using an Nd:YAG laser with wavelength 1.06 μm. Technically pure aluminum (95.50 wt. %) was used as the welded material. Eighteen welds (penetration passes) were fabricated in the experiment. Optical microscopy was used to assess the influence of changes in the parameters of the pulsed laser on the quality and geometry of the penetration passes of aluminum and on the hardness measurement through the interface of the welds. The results show that the geometry of the penetration passes was influenced above all by the position of the beam focus.

Influence on the dilution by laser welding of aluminum with magnetic stirring

The Aluminum 6xxx alloys are well-known for their high susceptibility to hot cracking. It has been reported that this problem can be effectively resolved by introducing silicon into the molten pool. However, the high welding speed by laser welding process results in an inhomogeneous dilution of the silicon, which may lead to hot cracks in the Sipoor area. The idea of applying a low frequency magnetic field during laser welding process has been already carried out recently in order to make a stir effect inside the molten pool and therefore to improve the element dilution in the weld joint.In this paper, the effects of the magnetic field on the melt flow as well as the element dilution are shown by applying copper as “tracer” inside the molten pool. Several methods were designed with different forms of copper at different positions in the workpieces to visualize the melt flow and the corresponding element dilution in different areas of the molten pool. In addition, laser welding with AlSi18 filler wire was also conducted to realize a real welding process comparing to that with “tracer”. WDX analysis was then carried out to investigate how silicon distributed inside the welds with the help of magnetic stirring. The results demonstrate that a DC magnetic field, with its direction coaxial to the laser, tends to modify the melt flow dynamics at flux density up to 100 mT. The results of laser welding with filler wire showed that by the help of an AC magnetic field with a frequency up to 10 Hz and flux density above 100 mT, the element dilution could be improved in the weld joint. The WDX analysis showed that under the influence of an alternating magnetic field a periodicity of the silicon distribution can be achieved, which depends greatly on the magnetic frequency.

On the Modeling of Plasma Dynamics in the Keyhole During Laser Welding of Metal With Deep Penetration

The physical processes occurring in a keyhole during deep penetration laser welding of aluminium are theoretically investigated. Evaporation, ionization and formation of low-temperature surface plasma on metal vapor can be observed. Equations of radiation flow dynamics are solved in the conjugated statement in assumption of equilibrium plasma. Numerical simulations of plasma propagation are conducted in one-dimensional approximation. Minimal value of laser power necessary for maintenance of the plasma is received. The affect of blocking of plasma self-radiation as a result of increasing its optical thickness is obtained. Results of the modeling are of interest for qualitative understanding of processes occurring in plasma, which may arise in a keyhole.

A Numerical Study of the Inclusion Problem in Electromagnetic Testing

Abstract The determination of magnetic distortion fields caused by inclusions hidden in a conductive matrix using homogeneous current flow needs to be addressed in multiple tasks of electromagnetic non-destructive testing and materials science. This includes a series of testing problems such as the detection of tantalum inclusions hidden in niobium plates, metal inclusion in a nonmetallic base material or porosity in aluminum laser welds. Unfortunately, easy tools for an estimation of the defect response fields above the sample using pertinent detection concepts are still missing. In this study the Finite Element Method (FEM) was used for modeling spherically shaped defects, and an analytical expression was developed for the strength of the response field including the conductivity of the defect and matrix, the sensor-to-inclusion separation, and the defect size. Finally, the results were adapted to Eddy Current Testing problems, in which the skin effect was taken into consideration for an appropriate estimation of the signal strength.

광 센서를 이용한 레이저 가공공정의 모니터링

In this paper, the monitoring system was developed measuring the light signal emitted from the plasma in aluminum laser welding. Spectrum of plasma was measured using a spectrometer, and the photodiode was selected based on the spectrum analysis. The sensor signals for various welding conditions could be obtained, the characteristic of signal was closely related to the intensity and stability of plasma through mean value of signal and FFT analysis. The reason of signal fluctuation was behavior of plasma and keyhole and it was also connected with the surface bead shape of weld.