Spot Welding Of Aluminum Research Articles

Toward Stabilizing the Keyhole in Laser Spot Welding of Aluminum: Numerical Analysis.

The inherent instability of laser welding, particularly keyhole instability, poses significant challenges in industrial applications, leading to defects such as porosities that compromise weld quality. Various forces act on the keyhole and molten pool during laser welding, influencing process stability. These forces are categorized into those promoting keyhole opening and penetration (e.g., recoil pressure) and those promoting keyhole collapse (e.g., surface tension, Darcy's damping forces), increasing instability and defect likelihood. This paper provides a comprehensive instability analysis to uncover key factors affecting keyhole and process instability, presenting future avenues for improving laser welding stability. Using a novel numerical method for simulating laser spot welding on aluminum with COMSOL Multiphysics 5.6, we investigated the effect of laser pulse shaping on keyhole and process instability. Our analysis focused on keyhole morphology, fluid flow behaviour, and force analysis. The results indicated that the curvature effect, Marangoni effect, and Darcy's damping force are primary contributors to instability, with the curvature effect and Darcy's damping force being the most dominant. Additionally, erratic and high-velocity magnitudes induce intense fluid flow behaviour, exacerbating keyhole instability. Moreover, single/quadruple peak triangular and variant rectangular ramp-down pulse shapes produced the least instability, while multi-pulse rectangular shapes exhibited intense instability. It was found that combining triangular/rectangular pulse shapes can reduce force and keyhole instability by smoothing spontaneous force spikes, resulting in a more stabilized welding process. Controlling fluid flow and abrupt force changes with appropriate pulse shaping is key to defect-free welded products.

Friction stir spot welding of aluminum alloy/steel plate with position-controlled joining equipment

Friction stir spot welding of aluminum alloy/steel plate with position-controlled joining equipment

Comparative Numerical Analysis of Keyhole Shape and Penetration Depth in Laser Spot Welding of Aluminum with Power Wave Modulation

Keyhole mode laser welding is a valuable technique for welding thick materials in industrial applications. However, its susceptibility to fluctuations and instabilities poses challenges, leading to defects that compromise weld quality. Observing the keyhole during laser welding is challenging due to bright process radiation, and existing observation methods are complex and expensive. This paper alternatively presents a novel numerical modeling approach for laser spot welding of aluminum through a modified mixture theory, a modified level-set (LS) method, and a thermal enthalpy porosity technique. The effects of laser parameters on keyhole penetration depth are investigated, with a focus on laser power, spot radius, frequency, and pulse wave modulation in pulsed wave (PW) versus continuous wave (CW) laser welding. PW laser welding involves the careful modulation of power waves, specifically adjusting the pulse width, pulse number, and pulse shapes. Results indicate a greater than 80 percent increase in the keyhole penetration depth with higher laser power, pulse width, and pulse number, as well as decreased spot radius. Keyhole instabilities are also more pronounced with higher pulse width/numbers and frequencies. Notably, the rectangular pulse shape demonstrates substantially deeper penetration compared to CW welding and other pulse shapes. This study enhances understanding of weld pool dynamics and provides insights into optimizing laser welding parameters to mitigate defects and improve weld quality.

Understanding the mechanisms behind ultrasonic vibration in resistance spot welding of aluminum and steel

An ultrasonic-assisted resistance spot welding process, which can improve the quality of aluminum/steel spot-welded joints, has been developed. However, the mechanism of the thermal-electrical-mechanical behavior caused by the ultrasonic longitudinal vibration to welding process has not been clarified. In this study, the role and impact mechanisms of ultrasonic longitudinal vibration during the welding process to form joints were confirmed by combining the microstructural characterization of the formed joints with the signal analysis of the process, as well as the analysis of the independent finite element numerical calculation results. Additionally, the interface metallurgical reaction behavior, welding defects, fracture behavior, and joint strength characteristics of ultrasonic-assisted aluminum/steel resistance spot welding joints were comprehensively analyzed, and the results indicated that the sizes of the aluminum/steel nuggets decreased. It could be attributed to the competition among multiple ultrasonic effects. Specifically, ultrasonic vibration decreased the contact resistance between the aluminum/steel sheets, whereas the acoustic cavitation and acoustic streaming effects increased the electrical conductivity of molten steel and thermal conductivity of molten aluminum, respectively. Moreover, ultrasonic vibration promoted the radial creep of molten and near-molten aluminum, which expanded in the effective bonding area between the two workpieces. Furthermore, ultrasonic vibration effectively reduced the thickness of the intermetallic compound layer (<3.0 µm), concurrently inhibited the formation of interfacial welding defects. Finally, the peak tensile-shear load of aluminum/steel joints is significantly increased under multiple ultrasonic optimization mechanisms.

Research on online intelligent welding system based on resistance spot welding of aluminum galvanized steel

The article follows a resistance spot welding system, which integrates a six-axis industrial robot, power supply, pneumatic actuator, welder, cooler, trimmer, software control system, welding analyzer, force feedback sensor and welding fixture to realize monitoring of welding quality and real-time adjustment of welding parameters. Taking the resistance spot welding of 6 series aluminum alloy and DC06 galvanized steel as a study, four groups of electrode combinations, 16-6/16-6, 16-10/16-10, 16-7/16-10, and 16-5/16-16 (steel side/aluminum side), are selected for simulation and analysis, and the electrodes are optimized with the simulation results. By selecting the optimal electrode combination to carry out experiments and analyzing the influence of welding current and welding time on the joint performance, the average pulling shear force of the aluminum alloy steel resistance spot weld head is finally realized to exceed the average pulling shear force of the aluminum alloy aluminum resistance spot weld head, and the fracture is all started from the parent material of the alloy side to achieve the failure of the button, and ultimately a good welding effect is achieved.

Friction stir spot welding of aluminum and steel sheets using a consumable sheet

Friction stir spot welding of aluminum and steel sheets using a consumable sheet

Advances in simulation and experimental study on intermetallic formation and thermomechanical evolution of Al–Cu composite with Zn interlayer: Effect of spot pass and shoulder diameter during the pinless friction stir spot welding process

In this study, the pinless friction stir spot welding of aluminum–copper composite with Zn interlayer was analyzed under experimental measurement and finite element method. The role of shoulder diameter, 16, 18, and 20 mm, and the number of spot pass, one to three pass, on microstructure, mechanical properties, and thermal history of weld samples were investigated. Based on the obtained results, there is a good agreement between numerical data and experimental analyses. It was shown that the heat source, due to plastic deformation and friction, increased as the shoulder diameter was increased, whereas the stress distribution in the weld samples was reduced. In addition, the thickness of the Zn interlayer at the joint interface changes when shoulder size increases from 16 to 20 mm, due to high temperature and intermixing between materials. From the microstructure analysis, the grain size in the joint zone gradually decreases as the spot pass increases from 1 to 3. It was concluded that the shoulder diameter of 16 mm with three spot passes showed the best result of 7.45 kN. Depending on X-ray diffraction analyses of the fracture surfaces, three primarily intermetallic phases including the Al2Cu, CuZn5, and CuZn2 were determined in the weld interfaces. Based on finite element method analysis, the axial compressive stresses showed the lowest profile as the shoulder diameter of the tool is 16 mm. Finally, the ductile fracture was detected as the main fracture mechanism for the joint sample with optimal joining conditions.

Hybrid resistance-laser spot welding of aluminum to steel dissimilar materials: Microstructure and mechanical properties

In this work, an innovative hybrid resistance spot-laser welding process, which first conducts resistance spot welding of aluminum and steel dissimilar materials, followed by laser spot welding, is proposed to join aluminum to steel. Through innovative designing of the electrode structure, the welding current distribution and the weld structure were optimized to produce a thin and uniform intermetallic layer with its thickness below 1.2 μm. Furthermore, the faying interface morphology of aluminum and steel dissimilar materials was changed from a traditional flat surface to an interface with a deep bulge into the aluminum weld. It was found that resistance spot weld had a considerable tensile-shear load but poor ductility and energy absorption due to the presence of a weak bonding area around the periphery of the joint, where facilitated the crack initiation and rapid propagation. The following laser spot welding process was conducted in the weak bonding area of the resistance spot welding joint, which inhibited rapid propagation of the cracks along the faying interface avoiding the interface fracture. Compared with resistance spot welding joints, the tensile-shear peak load and energy absorption were increased by 18.2 % and 424.8 % for hybrid welding joints, respectively.

Resistance Spot Welding of Aluminum 6063 Alloy for Aerospace Application: Improvement of Microstructural and Mechanical Properties

Resistance Spot Welding of Aluminum 6063 Alloy for Aerospace Application: Improvement of Microstructural and Mechanical Properties

Friction stir spot welding of aluminum and carbon fiber reinforced thermoplastic using hybrid surface treatment improving interfacial properties

In this study, the synergistic effects of a hybrid surface treatment involving hydrochloric acid (HCl) immersion and silanization on friction stir spot welding (FSSW) of aluminum and carbon fiber reinforced thermoplastic (CFRTP) were investigated. Maximum tensile shear strength of 10.2 kN and maximum cross-tension strength of 1.92 kN were achieved. An unloading test and a miniature tensile test revealed that the fracture behavior changed from interfacial to CFRTP fracture due to increased interfacial strength with the hybrid treatment and utilization of the CFRTP strength enhanced the joint strength. The nanostructures at the interface with HCl immersion treatment indicated that the interfacial properties were improved mechanically in addition to the chemical enhancement by silanization. Owing to the hybrid treatment, aluminum and CFRTP were efficiently joined by the adhesion behavior of spreading melted plastic resin during the FSSW process.

Capacitor Discharge Spot Welding of Aluminum, Part 1: Weldability Assessments

A key aspect of integrating automotive sheet into automotive production are the costs associated with joining. While the majority of sheet steel assembly is done with resistance spot welding, that has not readily translated to aluminum. Resistance spot welding of aluminum sheet is challenged by high current demand as well as reduced electrode life. In the latter case, direct current (DC) power supplied by state-of-the-art systems has exacerbated the problem. Recently, technology employing capacitor discharge (CD) welding in conjunction with polarity switching has been developed. This work is a first effort in examining the response of resistance spot welding on aluminum sheet to polarity-switching CD power. In this paper, the current range response between medium-frequency DC (MFDC) and polarity-switching CD was investigated. It was found that polarity-switching CD welding offered improved current ranges over MFDC. In addition, replicate mechanical testing cross-tension results were similar, but tensile shear strengths improved nominally 20–25%. Finally, some limited tests were done to assess the suitability of CD resistance spot welding in the presence of an adhesive. Current range tests with and without a prepulse were done, and both showed excellent weldability.

Experimental investigation and optimization of welding parameters on weld strength in friction stir spot welding of aluminum using Taguchi experimental design

Nineteen years ago, the automotive industry started using the friction stir spot welding (FSSW) process in joining metallic parts. The popularity of this welding process became higher every year. In this study, aluminum (Al) 1020 sheets of 2 mm thickness were joined with the FSSW process. The effects of FSSW parameters (plunge depth, tool rotation speed and dwell time) on the mechanical properties of weldments were investigated. The mechanical performance of the welds was evaluated by using the lap-shear tensile test. The optimization was done by using the Taguchi method. ‘The-higher-the-better’ quality control characteristic using the analysis of variance (Anova) method was applied to determine the optimum welding parameters. The signal-to-noise ratio was computed to calculate the optimal process parameters. The percentage contributions of each parameter were validated by using the Anova technique. The experimental results were analyzed by using the Minitab 17 software. The tool rotation speed was found as the dominant welding parameter on the weld strength of aluminum 1020 sheets for the FSSW process. The weld that had been produced with the optimum welding parameters gave a 23% higher fracture load than the initial welds.

Resistance Spot Welding of Aluminum to Aluminum Clad Steel Sheet: Experimental and Theoretical Analysis

Abstract In order to increase the cross-tension to the tensile-shear peak load ratio, aluminum clad steel sheet produced by roll bonding, was used for resistance spot welding to Al-Mg aluminum alloy. The results showed that the weld nugget formed between the aluminum clad layer and Al-Mg base sheet was the load bearing area. Presence of the metallurgical bond between the steel sheet and the aluminum clad layer led to the formation of the Al/Fe intermetallic compound with the thickness less than ∼3.5 μm. This narrow intermetallic layer did not play a detrimental role in the weld strength and therefore, the cross-tension to the tensile-shear peak load ratio reached up to ∼0.5 at the maximum tensile-shear peak load which was an advance compared to the results in the literature. Theoretical analysis was relatively successful for prediction of the critical nugget diameter and the tensile-shear peak failure loads. While the tensile-shear peak load increased with the welding current up to ∼4 kN, the peak load in the cross-tension test remained relatively constant at ∼2 kN.

Ultrasonic spot welding of aluminum to copper: a review

A comprehensive and integrated review about the current state of ultrasonic spot welding of aluminum to copper with numerous crucial issues containing materials flow, plastic deformation, temperature and stress distribution, relative motion, vertical displacement, and behavior of the aluminum oxide layer at the weld interface, as well as macrostructure, microstructure, mechanical properties, and electrical conductivity is provided. Meanwhile, the future trends in this field are offered.

Friction Stir Spot Welding of Aluminum and Copper: A Review.

Aluminum (Al) and copper (Cu) have been widely used in many industrial fields thanks to their good plasticity, high thermal conductivity and excellent electrical conductivity. An effective joining of dissimilar Al and Cu materials can make full use of the special characteristics of these two metals. Friction stir spot welding (FSSW), as an efficient solid-state welding method suitable for joining of dissimilar metal materials, has great prospects in future industrial applications. In this paper, the FSSW studies on Al-Cu dissimilar materials are reviewed. The research progress and current status of Al-Cu FSSW are reviewed with respect to tool features, macroscopic characteristics of welded joints, microstructures, defects in welds and mechanical properties of joints. In addition, some suggestions on further study are put forward in order to promote the development and progress of Al-Cu FSSW studies in several respects: material flow, thermal history, addition of intermediate layer, auxiliary methods and functionalization of Al-Cu FSSW joint.

Friction stir spot welding of aluminum and wood with polymer intermediate layers

Lap joints between aluminum and beech (Fagus longipetiolata) were obtained via friction stir spot welding with Nylon-66 intermediate layers. The polymer layer was introduced to form sandwich structures, which induced mechanical interlocking through infiltrating into the rough surface and formed chemical bonding via C-O-Al bonds. Wood degradation and residual stress were downgraded due to the buffering of the polymer layer. The maximum tensile shear strength with Φ12 mm circular lap area was 11.2 MPa, indicating that friction stir spot welding with thermoplastic polymer intermediate layers has the potential to join metals and woods with high performances.

Joint formation in ultrasonic spot welding of aluminum to copper and the effect of particle interlayer

Ultrasonic spot welded Al/Cu joints with and without Al2219 particle interlayer are successfully achieved. For the Al/Cu joints, as the welding energy increases, the T-peel failure load increases up to the maximum value at the welding energy of 1500 J, and then decreases; the hardness at the center of the cross-section is lower than that of the base metal; micro-joints expand until a strong interface bonding is established, excessive welding energy promotes the formation of sonotrode tip sticking. Under the action of Al2219 particle interlayer, significant mechanical interlocking and swirl-like flow are generated at the weld interface. The maximum T-peel failure load (336.8 N) of Al/Al2219/Cu joint is 32.3 % higher than that (254.6 N) of Al/Cu joint.

Exploration of bonding phenomenon and microstructural characterization during high-power ultrasonic spot welding of aluminum to steel sheets with copper interlayer

Abstract Lightweighting of automotive body structures involves the ultrasonic spot welding (USW) of dissimilar sheets because of its low energy consumption in comparison to the traditional fusion welding process. In this study, AA3003 aluminum alloy to AISI 304 stainless steel with a copper interlayer was joined using USW technique at different weld times. The tensile shear strength of Al-to-SS joint with Cu interlayer (95.9 MPa) exhibited a higher value of 20.17% than SS-to-Al joint with Cu interlayer (79.8 MPa). The softer Al side experienced interfacial failure (IF) modes at lower weld times and at higher weld times, it gradually transformed to nugget pull-out failure (NPF). A comparative lower hardness value was obtained in Al-to-SS joint with Cu interlayer, demonstrating the generation high interface temperature and rigorous plastic deformation. The precipitation of brittle intermetallic compounds (IMCs) on the fracture surfaces severely concedes the reliability of the weld joints.

Microstructure Development during Low-Current Resistance Spot Welding of Aluminum to Magnesium

Resistance spot welding of aluminum (Al5754) to magnesium (AZ31B) alloys results in the formation of a variety of solidification microstructures and intermetallic compounds that may affect the in-service performance of the weld. This study evaluates the relationship between the welding parameters and the properties of the weld nugget that is formed, and clarifies the morphological and microstructural evolutions within the weld regions during the low-current “small-scale” resistance spot welding of Al5754 to AZ31B. The investigations included a combination of microstructural characterization and thermodynamic analysis of the weld region. The results show that the welding time and clamping force parameters have significant effects on the properties of the nugget formed. The optimal welding parameters were found to be 300 ms welding time and 800 N clamping force. Weld nuggets formed with lower welding time and clamping force were undersized and contained extensive porosity. Meanwhile, a clamping force above 800 N caused gross deformation of the test samples and the expulsion of the molten metal during the welding process. The most significant microstructural changes occurred at the weld/base metal interfaces due to the formation of Al17Mg12 and MgAl2O4 intermetallic compounds as well as significant compositional variation across the weld pool. The thermal gradient across the weld pool facilitated the formation of several microstructural transitions between equiaxed and columnar dendrites.

Use of a Zener Approximation for Heat Transfer Analyses of Quasi One-Dimensional Welding Problems

Most welding methods in use today involve heating and subsequent cooling of the substrates for joining. Not surprisingly, understanding of associated thermal cycles implicit with the various processes has been a key facet of welding research. While the tools are available for sophisticated numerical solutions, much insight can be gained from simplified analytical approaches. A wide range of joining technologies in use today can be addressed by nominal one-dimensional heat transfer analyses. These include, for example, resistance spot, flash-butt, and linear friction welding. In addressing heat transfer problems, the mathematical constructs for heat transfer are analogous to those for mass (diffusion) transfer. Not surprisingly, one dimensional heat transfer problems can be greatly simplified by adapting the Zener approximation from mass transfer. The work described here employs the Zener approximation to address the direct spot welding of aluminum to steel. The Zener approximation is used to understand heat flow progressively from the steel into the aluminum and finally the copper electrodes. The results are used to understand weld morphology and implicit cooling behavior