Welded Aluminium Alloy Joints Research Articles

Effect of swinging laser on porosity, microstructure, and mechanical properties of laser welded aluminum alloy joints with different lap forms

Oscillating and conventional linear laser welding were conducted to enhance the bonding strength of dissimilar aluminum alloys. The effect of lap joint configuration on porosity, microstructure, and mechanical properties of laser-welded dissimilar aluminum alloy joints was investigated. It was found that the solidification rate of the melt pool was the dominant factor in the difference in porosity for oscillating laser-welded joints with different lap joint configurations. The main precipitated phase in welds with different lap joint configurations was eutectic Si, and the proportion of eutectic Si was higher in oscillating laser welds than in linear laser welds. The elemental distribution in oscillating laser welds was more uniform. The strengthening mechanism for tensile shear strength of oscillating laser welded lap joints was analyzed. The improved tensile shear strength and elongation were attributed to the reduced porosity and solid solution strengthening for the oscillating laser welding. The tensile strengths of the two lap types of oscillating laser welded joints increased by 25.1 MPa and 34.5 MPa, and the elongation increased by 0.7% and 4.5%.

Physical and Mechanical Properties of Butt Welded Joints of Aluminum Alloys

Along with the improvement of joining technologies with argon arc, plasma and laser welding for aluminum alloy elements, high efficiency of joints made with the use of friction stir welding (FSW), which has low energy consumption and is almost equally strong as base metal, has been achieved. However, the processes of friction stir welding have not been sufficiently studied and can lead to softening of aluminum alloy welds up to 0.65 of base metal strength. When studying the effect of friction stir welding and mechanized electric arc welding in argon medium, welded joints of aluminum alloys of Al-Si-Mg (AD35T1, 6082-T6) and Al-Zn-Mg alloying systems (1915T) were subjected to tensile and impact tests. The values of strength, elastic and plastic characteristics of argon arc welded specimens of 1915T, AD35T1 and 6082-T6 alloys were obtained. For alloy 6082-T6, the same characteristics are presented for FSW welded specimens. Decrease in strength and ductility in the zones of welded joints for both welding methods is observed. At the same time, the highest relative values of strength and offset yield strength of the welded joint are fixed for friction stir welding. Slight decrease in modulus of elasticity obtained for argon-arc welded specimens was recorded. The impact strength is constant for each welded joint zones in the temperature range of +20 – -60оC and increased in weld metal of FSW butt joints of alloy 6082-T6.

Effect on microstructure and mechanical properties of friction stir welded 5A06 aluminum alloy joints by deep cryogenic treatment

In order to improve the comprehensive mechanical properties of the welded joints of the 5A06 aluminum alloy, friction stir welded (FSW) joints were subjected to deep cryogenic treatment (DCT). The microstructure and mechanical properties were characterised using metallographic microscopy, x-ray diffractometer (XRD), energy spectrometer, microhardness tests, and tensile tests. The experimental results show that DCT refines the structure significantly due to the large temperature difference. This refinement results from an increase in Mg atoms within the α-Al solid solution through the precipitation of Al atoms, forming the Al3Mg2 phase. This enhancement in plasticity is achieved through dispersion distribution. Moreover, as the treatment time of DCT increases, the mechanical properties of the welded joint also improve significantly. The microhardness of the welding joint peaked at DCT3h, rising from 78.8 HV at DCT0h to 87.2 HV at DCT3h. Meanwhile, the tensile strength of the joint reached its maximum at DCT12h, rising from 358.7 MPa at DC0h to 385.3 MPa at DCT12h, representing a 7.4% increase. These experimental results underscore the significant impact of DCT on improving the welded joints.

Improving the Formation and Quality of Weld Joints on Aluminium Alloys during TIG Welding Using Flux Backing Tape

This work aimed to compare the quality and properties of the welded joints of AMg6 aluminium alloy produced via conventional TIG welding with the properties of those produced with flux backing tape. This study focussed on the relative length of oxide inclusions (Δoi) and the amount of the excess root penetration (hroot) of the AMg6 alloy weld beads. The results show the influence of the thickness of the flux layer of the backing tape on the formation and quality on the AMg6 alloy welds, along with the effect of flux backing tape and edge preparation on the mechanical properties of the 6 and 8 mm thick welded plates. In accordance with the results obtained, the joints produced by means of TIG welding with flux back backing tape and without edge preparation have higher mechanical properties. Moreover, the TIG welding of AMg6 alloy using flux backing tape reduces the total welding time by 55%, reduces filler wire consumption by 35%, reduces shielding gas consumption by 43% and electricity consumption by 60% per 1 linear meter of the weld line.

Microstructure Evolution and Mechanical Properties of Thick 2219 Aluminum Alloy Welded Joints by Electron-Beam Welding.

In this study, 2219 aluminum alloy thick plate was joined by electron beam welding. Defect-free joints with excellent surface formation were obtained. There were significant differences in the microstructure along the thickness direction of the weld zone (WZ). The upper region of the WZ was mainly striated grains, while the lower region was fine equiaxed grains. The WZ of 2219 joint is composed of α-Al and Al-Cu eutectic. Fine equiaxed grains were formed in the partially melted zone (PMZ) due to the existence of high-melting nucleation particles including Ti-Al and Ti-Zr compounds. The eutectic microstructure in the PMZ and the heat-affected zone (HAZ) presented net-like and block-shape distribution. Due to the formation of fine grains and high content of Al-Cu eutectic, the WZ showed the highest microhardness (80 HV). Therefore, the 2219 joint obtained excellent mechanical properties. The tensile strength of the 2219 joint was equal to that of the base metal (BM), but the elongation of the 2219 joint significantly decreased to 15.1%, about 67.7% of that of BM. The fracture mode of the 2219 joint presented typical ductile fracture.

Effect of post-welding coating process on the organization and properties of MIG-welded T-joints of 6063-T6 aluminum alloy

Abstract With the rapid development of the precision industry, aluminum alloy structural parts have been widely used. However, in the welding process of aluminum alloy, there are problems such as welding deformation and weld tumor defects due to the special physical characteristics of aluminum alloy. Therefore, this paper mainly focuses on 6063-T6 aluminum alloy as the research object to analyze the effect of the coating process on the organizational properties of MIG welded T-joints of 6063-T6 aluminum alloy. First, based on the Simufact welding finite element analysis platform, the establishment of a three-dimensional welding simulation model, the simulation calculations and test results for comparison, the peak temperature and temperature change trend of each measurement point between the two. Secondly, according to the T-joint welding process, welding numerical simulation of 6063-T6 aluminum alloy rear compartment structural parts to obtain the rear compartment assembly welding residual stress is mainly concentrated in the vicinity of the weld. Finally, the impact of welding current on the organization and properties of T-shaped welded joints of 6063-T6 aluminum alloy was discussed. The results show that the coating process has a good strengthening effect on the mechanical properties of welded joints. Compared with the pre-coating process, the welded joint tensile strength increased by 14.93%, and the welding coefficient of 73% of the parent material heat-affected zone microhardness increased by 21.82% compared to the pre-coating process. In this paper, the finite element theory of the coating process and MIG welding, T-joint organization between the found welding heat-affected zone after the coating process can make Mg, and Si atoms continue to be enriched, and mechanical properties strength is enhanced.

Notch-Stress S–N Curves for Welded Aluminum-Alloy Components Subjected to Bending

Fatigue analysis of aluminum-alloy welded joints based on the linear elastic notch-stress approach is presented in this paper. The International Institute of Welding proposes two variants of the approach, one for thick joints, i.e., joints with a plate thickness of 5 mm or more, with a reference radius rref = 1 mm, using the FAT71 notch-stress design curve, and one for thin joints, i.e., joints with a plate thickness of less than 5 mm, with a reference radius rref = 0.05 mm, using the FAT180 notch-stress design curve. In this work, the feasibility of the proposed S–N curves, obtained mainly by fatigue tests on axially loaded joints, was investigated for 4 mm thick joints subjected to bending. The fatigue analysis was performed for two types of joints: a joint with longitudinal fillet-welded attachment and a joint with round sheet fillet-welded attachment. It was shown that a more accurate estimation of the fatigue life of 4 mm thick aluminum joints loaded in bending can be obtained using the FAT71 notch-stress design curve.

Development of novel Al-Si-Ce filler wires to enable high contrast in X-ray imaging of fusion welded aluminum alloy joints

Development of novel Al-Si-Ce filler wires to enable high contrast in X-ray imaging of fusion welded aluminum alloy joints

Tensile properties and microstructure of surface tension transfer (STT) arc welded AA 6061-T6 aluminum alloy joints

The wide usage of 6xxx series aluminium alloys in automobile sector is mainly because of the exceptionally good weldability characteristics and better corrosion resistance. Surface tension transfer (STT) arc welding is one of the variants of gas metal arc welding (GMAW) that has potential features such as low heat input and arc stability with an innovative wire feed system. STT is a modified short-circuiting metal transfer technique that regulates the metal transfer rate using a high-frequency inverter power supply This process is widely used in automobile industry due to its higher welding speed and capability to weld thin sheets without defects like spatter, distortion and burn through. This article reports the welding of thin aluminium 6061 sheets by STT arc welding process and presents the tensile properties of the welded joints. The features of the microstructure are characterized by optical microscopy. The fracture surfaces are being examined by scanning electron microscopy. During the tensile test, the welded joint failed at 12 mm from weld zone. It is evident that failure is generated by softening in (heat affected zone) HAZ region due to the production of β′or β precipitates which are softer and incoherent in nature. The tensile properties of STT welded aluminium alloy joints yielded a better joint efficiency of 71.08 % due to the presence of higher hardness in the welded region. The hardness results signify that the HAZ noted low hardness which is called as softened zone, where the transformation of precipitates or coarsening of grains takes place.

Non-destructive testing of an aluminum alloy welded joint based on a mathematical model of the thermal welding process and computer microtomography

Strength control of welded joints is used in many industries. X-ray microtomography as a method of non-destructive testing allows not only to detect the presence of defects, but also to classify them and assess the size of cracks and non-crack-like defects (pores). This article discusses the non-destructive testing of welded joints of aluminum alloy 6061 T6 using computer micrototomography and a mathematical model of the thermal welding process implemented in ANSYS Workbench. Experimental results of the X-ray microtomograph are presented, and the size of defects in this sample is estimated. The mathematical model allowed us to obtain the thermal histories at which the faults were formed.

Comprehensive fatigue assessment for different types of aluminum fillet welded joints by local approaches

This paper investigates different types of MIG-welded fillet joints (lap welded joints, T welded joints, non-load-carrying cruciform welded joints, load-carrying cruciform welded joints) of 7N01 aluminum alloys under fully reversed pulsating axial loading. Fatigue assessments of the as-welded test results based on nominal, and local approaches are performed considering geometrical factors in different types of welded joints. The fatigue strength for these joints was compared with the international standard codes and those of other materials. Subsequently, the geometric parameters on the fatigue characteristic indicators in different types of welded joints were studied systematically by combining finite element calculated results and analytical methods, such as weld length, notch angles, incomplete penetration length, et al. The results show that the 7N01 lap welded joint owns the lowest fatigue strength (29 MPa) at 2*106 cycles. The corresponding geometrical analytical solutions of local fatigue indicator Strain Energy Density (SED) were established for these welded joints, which could quantitatively describe the fatigue characteristic relationships among different types of welded joints. The theoretical predictions based on SED notch geometric semi-analytical models are relatively higher than the recommended design curves of other local approaches.

Revealing the mechanism of laser welded aluminum alloy joints in-situ reinforced by carbon nanotubes based on microstructural evolution

In-situ addition of carbon nanotubes (CNTs) was innovatively applied to laser welding Al-Cu-Mg alloys to form composite joints, and the mechanism of CNTs strengthening joints was revealed from the viewpoint of microstructure evolution. Tensile test showed that the average tensile strength of the CNTs-reinforced joint increased by 37.3% to 306 MPa. Initially, microscopic observation and elemental analysis found that part of the CNTs were combined with the precipitate, and part of the CNTs were dispersed in the matrix, which provided conditions for the transfer of the load from the matrix to the CNTs. In addition, the fusion zone (FZ) grains of the joints in-situ strengthened by CNTs are finer and isotropic compared to the joints without CNTs. Since CNTs and aluminum alloys have remarkable differences in thermal expansion coefficients to form thermal mismatches, and part of CNTs may act as grain boundaries, resulting in dislocations cannot cut through them to form Orowan strengthening. As a result, CNTs-reinforced joints achieved significant improvements thanks to these primary strengthening mechanisms. The mechanism of CNTs-strengthened aluminum alloy joints is comprehensively and deeply revealed from the microscopic level, which provides a reference for the design of Al/CNTs composite joints and performance regulation.

Carbon emission modeling and mechanical properties of laser, arc and laser–arc hybrid welded aluminum alloy joints

Reducing environmental impact while achieving desired processing performance is increasingly sought after. Various welding processes are widely employed in advanced manufacturing, but their carbon emission characteristics vary. However, few studies have compared the carbon emissions of different welding methods. Therefore, it is urgent to analyze the carbon emission characteristics of commonly used welding methods, and to consider the welding performance for a comprehensive comparison. In this study, we construct the carbon emission models of three welding methods (laser, arc, and laser–arc hybrid welding) by building the monitoring platform. The characteristics and proportions of carbon emissions of each system in three welding methods are analyzed. Additionally, the bead morphology, microhardness, and microstructure of aluminum alloy joints are investigated to explain the results of tensile tests. The experimental results show that the appropriate welding heat inputs (WHI) of laser, arc, and laser–arc hybrid welding lead to the ultimate tensile strength (UTS) of 229.1 ± 2.6, 186.1 ± 3.0, and 250.0 ± 0.8 MPa, with the carbon emissions of 43.12, 26.06, and 120.25 g respectively. However, the carbon efficiency of laser–arc welding is lower than laser welding, while arc welding has the lowest carbon efficiency and the highest carbon emission. Increased welding speed can help reduce carbon emissions. For each welding method, properly penetrated joints have better tensile properties than joints with insufficient or excessive WHI, and too high WHI results in low carbon efficiency due to increased carbon emissions and decreased UTS. The welding process with lower WHI help to narrow the fusion zone (FZ) and heat affected zone, and refine the grains in the FZ. This study provides an empirical understanding on the relationship of welding method–carbon emission characteristic–mechanical property.

Entire-Process Simulation of Friction Stir Welding — Part 2: Implementation of Neural Networks

To further understand the structure-parameter-property relationships of friction stir welded aluminum alloy joints, a nested neural network was proposed to map the macro- and microstructural response. The uncoupled effect of each primitive parameter on the joint performance was depicted. Reducing heat input and keeping an adequate load-bearing area of the welding nugget zone were proven to be the sufficient and necessary conditions to obtain high load-bearing performance. The entire-process simulation strategy showed great potential for prediction and optimization of the macro- and microstructural response of complex and large components.

Bonding mode and mechanical properties of keyhole-free friction stir rivet welded aluminum alloy joints

A novel method called friction stir rivet welding (FSRW) is proposed to combine mechanical interlocking and metallurgical joining, and is expected to improve such mechanical properties and eliminate the keyhole defects in traditional friction stir spot welded (FSSW) joints. The FSRWed joint forms metallurgical joining between the upper and lower sheets, while mechanical interlocking between the rivet and the surrounding plasticized materials. The spindle force, bonding mode, mechanical properties and failure mode of three joints are comparatively investigated to clarify the strengthening mechanism of FSRW method. Results indicate that the keyhole defects are successfully eliminated in FSRWed joints, and the mechanical properties of the joints are considerably improved by using the threaded rivet FSRW (T-FSRW). The spindle force requirement of T-FSRW exhibit greater than that of cylindrical rivet FSRW (C-FSRW). Similarly, compared with the FSSWed joint, the T-FSRWed joint has a 65% higher shear tension strength and 170% increase in cross tension strength, with the corresponding extension at fracture increased by 19% and 220%, respectively. Rivet geometry plays a crucial role on the joints’ mechanical properties, and determines the transverse section and joining parameters. The strengthening mechanism of the FSRW method is assumed from the combination of mechanical interlocking and metallurgical joining. In addition, analysis of the fracture morphologies demonstrate that the shear tension failures of the FSRWed joints mainly exhibit neck, shear fracture and upper sheet tensile fracture, while the cross tension failures exhibit neck fractures and rivet pull-outs.

Research on Microstructure and Mechanical Properties of CMT and MIG Welded Joints of A6N01 Aluminum Alloy

Cold metal transition welding (CMT) and molten inert gas shielded welding (MIG) two welding processes were used to conduct butt welding tests on 2mm thick 6N01 aluminum alloy, and the microstructure and mechanical properties of the welded joints obtained by the two processes were tested.The results show that the welded joints of 6N01 aluminum alloy welded by CMT process have better appearance and less welding defects and welding spatter. The tensile strength of CMT welded joints is 213MPa and the elongation after fracture is 10.64%, which is slightly higher than that of MIG welded joints. The hardness distribution of CMT and MIG welded joints and the hardness values of each zone are basically the same. Compared with MIG welded joints, the grain structure of CMT welded joints and the equiaxed crystals on the side of the fusion zone near the base metal are smaller and more uniform.

Tensile Behaviour of Friction Stir Welded Joints of Different Aluminium Alloys

This paper investigates the outcome of base metals and their temper condition on tensile and fracture behavior of friction stir welds of various work and precipitation hardening aluminium alloys in different tempers (AA1100-O, 5052-H, AA5086-O & H25, AA2024-O & T6, and AA6061-T651). The type and temper of aluminium alloys affected the tensile, and fracture behavior of weld joints. The extent of improvement in tensile properties of welded joints increased with a decrease in hardness (i.e., from T6 or H to O) of base metals. Softening was not observed for welded joints when base metal was in an annealed temper and an opposite trend was observed for hardened tempers ‘H’ and ‘T6’. Fracture location moved towards the weld centre with the change in temper from ‘O’ to ‘H’ and ‘T6’, hardness minima were closer to base metal hardness in the first case than later. The mode of fracture was ductile for all the weld joints except AA2024-T6 and AA 6061-T651. Except for AA2024-T6 and AA 6061-T651, all weld joints had ductile fracture mode.

Microstructure and stress corrosion behaviour of CMT welded AA6061 T-6 aluminium alloy joints

Superior properties of AA6061 grade aluminium alloys are finding greater use in automotive, marine and aircraft applications due to its strength, weldability and high corrosion resistance. But it is highly susceptible to stress corrosion cracking owing to alter the phase composition and microstructure during welding process. In the present work, an experimental study of stress corrosion cracking is conducted on Cold Metal Transfer welded aluminium alloy joints using various heat input under constant stress intensity to understand the susceptibility of various zones to Stress Corrosion Cracking and the performance has been analysed using Tafel electrochemical technique. The result shows that the mechanism of cracking is established to be anodic mode with transgranular nature of crack propagation. In addition, a linear relationship is also inferred to predict the time to failure by extrapolating the rate of steady state elongation. The integrity of the dissimilar joints are analysed with the help of Optical Microscopy, SEM, EDAX and XRD sophisticated analytical techniques.

Review of Techniques for Improvement of Softening Behavior of Age-Hardening Aluminum Alloy Welded Joints.

The softening phenomenon of age-hardening aluminum alloy-welded joints is severe during conventional fusion welding, which increases the likelihood of stress and strain concentration in the joint during the period of service, significantly reduces the mechanical properties compared to the base metal, and represents an obstacle to the exploration of the potential structural performance. This review paper focuses on an overview of the softening phenomenon. Firstly, the welding softening mechanism and the characteristics of age-hardening aluminum alloys are clarified. Secondly, the current main research methods that can effectively improve joint softening are summarized into three categories: low-heat-input welding, externally assisted cooling during welding, and post-weld treatment. The strengthening mechanism and performance change rule of age-hardening aluminum alloy joints are systematically analyzed. Finally, this paper considers the future development trends of further research on joint softening, and it is expected that interest in this topic will increase.

Evaluation of the Possibility of Obtaining Welded Joints of Plates from Al-Mg-Mn Aluminum Alloys, Strengthened by the Introduction of TiB2 Particles

In the work, the possibility of obtaining strong welded joints of aluminum alloys modified with particles is demonstrated. For research, strengthened aluminum alloys of the Al-Mg-Mn system with the introduction of TiB2 particles were obtained. TiB2 particles in specially prepared Al-TiB master alloys obtained by self-propagating high-temperature synthesis were introduced ex situ into the melt according to an original technique using ultrasonic treatment. Plates from the studied cast alloys were butt-welded by one-sided welded joints of various depths. To obtain welded joints, the method of electron beam welding was used. Mechanical properties of the studied alloys and their welded joints under tension were studied. It was shown that the introduction of particles resulted in a change in the internal structure of the alloys, characterized by the formation of compact dendritic structures and a decrease in the average grain size from 155 to 95 µm. The change in the internal structure due to the introduction of particles led to an increase in the tensile strength of the obtained alloys from 163 to 204 MPa. It was found that the obtained joints have sufficient relative strength values. Relative strength values reach 0.9 of the nominal strength of materials already at the ratio of the welded joint depth to the thickness of the welded plates, equal to 0.6 for the initial alloy and in the range of 0.67–0.8 for strengthened alloys.