Joining Aluminum Alloy Research Articles

Influence of rivet structure on the bonding mechanism and mechanical properties of carbon fiber reinforced polyphenylene sulfide‐AA7075 friction stir blind riveted joint

AbstractThis paper reports an experimental investigation into joining mechanism and mechanical properties of carbon fiber reinforced polyphenylene sulfide (CF/PPS)‐AA7075 friction stir blind riveting (FSBR) joints made of different structure rivets. Four types of rivets were obtained by second machining of the commercial rivet, the corresponding FSBR test were conducted. Penetration forces and temperatures during friction penetration process were collected. The joint quality, tensile shear strength, and failure mode of the four types of joints were compared. The results demonstrated that the joint quality and mechanical behavior of the FSBR joint were highly related with the rivet tip structure. Compared with the original commercial rivet, machining rectangular or triangular slots at the rivet tip can increase the cutting proportion during FSBR process, which will reduce material damage, penetration force, flash and the gap between the two workpieces. The premature mandrel breakage caused joining failure can be effectively avoided by introducing slots at the rivet tip. Rivet with four triangular grooves was the most effective, can reduce penetration force by 14.9%, increase joint tensile shear strength by 10.9% and increasing fatigue life up to five times that of original commercial rivet.Highlights FSBR technology is firstly applied to the joining of aluminum alloy with CFRTP. Rectangular or triangular slots are machined at the tips of commercial rivets. Forming quality, tensile strength, and failure mode of joints were evaluated. Probability of joining failure is effectively reduced. Joint tensile strength has increased by 10.9% and fatigue life up to five times.

Performance evaluation of modified refill friction stir riveting process on AA7075-T6 stacks with largely unequal thicknesses

Aluminium alloy sheets with varying thicknesses have been intensively applied to thin-walled structures in the transportation industry. However, it is still a challenging work to assemble lightweight stacks with largely unequal thicknesses (i.e., A thick top sheet but a thin bottom sheet). In this research, a modified refill friction stir riveting (RFSR) technique was developed to connect AA7075-T6 aluminium alloy stacks with 3.2 mm top sheet and 1.0 mm bottom sheet. The joint geometric quality, microstructures, thermal softening state and tensile strength were experimentally investigated. The results reveal that the modified RFSR approach is capable of joining aluminium alloy stacks with largely unequal thicknesses. A reliable mechanical interlock was generated between the rivet and bottom sheet, benefiting from the drum-shaped buckling behaviour of the rivet shank in the modified RFSR process. Thanks to the high pressure in the rivet cavity and high rotation speed of top sheet material locked on the rivet shank, solid-state bonding with a high quality was always generated between the trapped top sheet and bottom sheet at varying feed rates. The feed rate demonstrated a strong controlling effect on the joint formation quality by altering the buckling degree of the rivet shank. Benefiting from the minor insertion depth of the rivet shank into the bottom sheet, the structural integrity of the thin bottom sheet was successfully retained. The maximum lap-shear force of studied joints was 4.78 kN with the feed rate of 1.0 mm/s, whilst the maximum cross-tension force was 1.49 kN with the feed rate of 4.0 mm/s.

Research on the Cavitation Resistance Testing of Friction Stir Welded Joint of En Aw 1200 Aluminium Alloy

Aluminium alloys are being used more often as a result of industry demands for strong, lightweight materials. Because of its advantages over conventional fusion welding techniques, friction stir welding, or FSW, has become a promising technique for joining aluminium alloys. Nonetheless, there is still cause for concern regarding FSW joints' vulnerability to cavitation erosion, which is a major issue in applications exposed to harsh environments. The cavitation resistance of EN AW 1200 aluminium alloy joints made by the FSW process is the main objective of this study. By utilizing specialized equipment to conduct cavitation tests, the study uses a comprehensive methodology to assess the cavitation erosion behaviour of these joints. A number of variables are investigated in order to determine how they affect the cavitation resistance of the welded joints, including mechanical attributes, welding parameters, and microstructural features. The goal of the study is to shed light on how well FSW joints function and hold up in cavitation scenarios. This information will be useful in improving the dependability and suitability of EN AW 1200 aluminium alloy in sectors where the ability to withstand cavitation erosion is critical. The findings from this study are expected to contribute to the optimization of welding parameters and material selection, ultimately advancing the use of aluminium alloys in critical applications requiring resistance to cavitation-induced damage.

Effect of process temperatures on joining aluminum alloy (AA5052) to polypropylene (PP) by friction lap welding

The joining of aluminum alloy 5052 (AA5052) and polypropylene (PP) by friction lap welding (FLW) was investigated under different process temperature conditions. Welding experiments were conducted at different tool rotational speeds, and the process temperatures were monitored using an infrared camera and thermocouples. The temperature distribution at the cross-section was determined using a validated numerical model. The joint quality was assessed by measuring tensile shear strength and examining the joint morphology. It was found that interfacial temperatures in the range of 156 °C–316 °C were optimal for achieving effective mechanical interlocking, attributed to the appropriate flow of molten PP into the textured aluminum alloy surface. Temperatures below 130 °C resulted in inadequate PP flow, leading to poor joint formation, while temperatures above 316 °C caused over-melting of PP, bubble formation, and approached the PP initial decomposition limit. Raman spectroscopy showed that the process temperatures did not cause significant chemical bonding and that mechanical interlocking was the main contributing joining mechanism. The results showed that dissimilar welding of metals and non-polar polymers can be optimized by the precise monitor and control of the temperature of the process.

Dissimilar joining of aluminum alloy and low-alloy carbon steel by resistance spot welding

In this work, the resistance spot welding (RSW) process was performed to join aluminum alloy and low-alloy carbon steel plates. The macro characteristics including nugget diameters and indentation rates, microstructure and tensile-shear strength of RSW joints were investigated. The results showed that the nugget of the RSW joints comprises a ‘bowl’ shape nugget on the aluminum side and an elliptical shape nugget on the steel side. Also, the intermetallic compound (IMC) layers containing Fe4Al13 and Fe2Al5 were formed around the aluminum/steel interface with the steel side having a tongue-shape and the aluminum side having a needle-shape. According to metallurgical evaluation and temperature distribution of RSW joints analyzed by the finite element method, the nugget on the aluminum side contained the dendritic grains and equiaxed dendritic grains. The nugget on the steel side consisted of a large amount of bainite and a small amount of coarse lath martensite. The nugget diameters and the indentations rates of RSW joints increased when increasing either welding current or welding time, and decreased when increasing the electrode pressure. The maximum values of nugget diameter and indentation rate of RSW joints were 9.076 mm and 4.144% when using the welding current of 16 kA, welding time of 450 ms and electrode force of 3 kN. In tensile-shear tests, the RSW joints showed a shear-off fracture mode. When increasing the welding current, welding time or electrode force, the tensile-shear strength of RSW joints increased first, and then reached a maximum, and finally decreased. The welding current of 16 kA, the welding time of 300 ms, and the electrode pressure of 3 kN were considered as the optimal welding parameters in the present study which resulted in the maximum tensile-shear strength of 2.24 kN. In addition, the IMC layers of the RSW joints exhibited a uniform and continuous appearance with a thickness of approximately 1.9 μm, and the IMC layer in the central area was thicker than that in the edge area.

Effects of Tool Geometry Parameters on Clinched Joint Strength Using FEM

Abstract Clinching joining is one of the predominant techniques used to join aluminium alloys in the automotive industry. Although the technique can be easily automated, cost-effective, and not affect the material’s mechanical properties during the joining process, the tool geometry parameters significantly affect the strength of the clinched joint. Therefore, a precise finite element model is critical to improve the strength and reduce the cliched joint’s production cost. This study investigated the effect of the punch fillet radius, the punch angle, the die diameter and the die depth on the strength of the clinched joint of 5754 aluminium alloys. The clinched joint was produced with different geometry parameters. The cross-section of the clinched joints was observed. In the meantime, the interlocking value, the neck thickness, and tool parameters were measured to investigate the joinability of the aluminium alloys. The static tensile shear tests were also conducted using the universal tensile machine. Numerical studies have been conducted to analyse the influence of the geometrical parameters using a 2D axisymmetric model. As a result, the numerical results agreed with the experimental results. Additionally, the result showed that the tool geometry significantly impacted the strength of the clinched joint of aluminium alloys. The study concluded that the neck thickness and the interlocking value have played a vital role in the enhancement of the cliched joint strength.

Influence of laser texturing on the properties of fusion joints between aluminum alloys and carbon fiber reinforced thermoplastic composites

Laser texturing is an effective method to enhance the fusion joining of aluminum alloy (Al) to carbon fiber reinforced thermoplastics composite (CFRTP). The enhancement effect is related to the morphology and spacing of the microstructures on Al surface. However, because of the correlation between the morphology and the spacing of the microstructures, excessive dense microstructures change the morphology, leading to a reduction in the enhancement effect, while sparse microstructures are also difficult to significantly enhance the joint. To this end, this paper proposes an improved laser texturing process to enhance fusion joints, through the investigation of the recast layer formation process during laser texturing on the Al surface, which comprehensively reveals the synergistic effects of microstructural morphology and spacing on joint properties. The results indicated that the increase of the number of laser processes and the microstructure spacing increased the height of the recast layer, with the difference that the microstructure spacing had less effect after increasing to a certain value. With the increase of microstructure spacing, the morphology of the microstructure on the Al surface transformed from the serrated microstructure to the double-scale microstructure, and finally to the independent microstructure, affected by the recast layer on sides of the microstructure. Once the dual-scale microstructures were formed on the Al surface, the shear strength of the Al/CFRTP fusion joint was the highest with a value of 25.05 MPa. The findings could provide a basis for laser texturing pretreatment for fusion joining.

Characteristics analysis and monitoring of friction stir welded dissimilar AA5083/AA6061-T6 using acoustic emission technique

The joining of aluminum alloys using fusion welding often leads to issues such as hot tears, porosity, distortion, and solidifying cracks. To address these challenges, solid-state welding processes like Friction Stir Welding (FSW) are preferable. This study investigates the FSW of dissimilar aluminum alloys AA 5083 and AA 6061-T6, employing Acoustic Emission (AE) techniques for real-time monitoring. FSW was conducted under conditions with no defects, pinhole defects, and piping defects. The resulting joints were evaluated for their mechanical properties and metallurgical characteristics. Microstructural analysis was performed using an optical microscope, revealing that the defect-free condition achieved the highest tensile strength of 256 MPa and superior hardness of 93 HV at the stir zone. Tensile failure commonly manifested within the heat-affected zone (HAZ) of AA 6061-T6, primarily due to grain enlargement and the impact of Mg2Si precipitates. Examination of the fractured regions via scanning electron microscopy revealed ductile-mode fractures featuring elongated dimples and microvoids. AE parameters such as hits, amplitude RMS, and energy were analyzed, demonstrating that defect-free welds had consistent AE signal patterns, while significant variations were observed in pinhole and piping defect conditions due to larger defect areas. The findings suggest that AE monitoring is effective in detecting and analyzing welding defects, providing valuable insights into the FSW process for dissimilar aluminum alloys.

Joining of Al-Alloy Tubes by Carbon Steel Tubes using MPW Technique

Background/ Objectives: Joining aluminum alloys with low carbon steel (DC01) through fusion welding is a challenging task due to the occurrence of solidification defects like porosity, alloy segregation, and hot cracking. However, these issues can be addressed by employing solid-state welding techniques like explosive welding and MPW (magnetic pulse welding). MPW is a cost-effective and high-speed solid state welding method that involves creating joints in an overlap configuration. Methods: The MPW technique was employed to join dissimilar aluminum alloy AL 7075T6 hollow tube and DC01 steel rod in this study. A central composite design model was created to analyze the relationship between key MPW process parameters, including stand-off distance (SoD), overlap length, and discharge energy, and the bonding strength of the joints. Experimental setups were established and correlate with tensile-shear fracture load and interface hardness of the joints with the MPW process parameters. Findings: It is understood that the maximum TSFL of 2.404 kN was obtained under the welding condition of 23kJ discharge energy, 2.25 mm Stand-off distance, 8.5 mm overlap length, which is the optimum MP welding state for AA 7075 T6 with DC01 and confirmed by RSM. In addition, the cultivated connection can be aptly leveraged to anticipate the TSFL of MPW joints with a 95% confidence level. Novelty: The parametric mathematic samples were developed for forecasting TSFL of joints. The MPW parameters were optimized to enhance TSFL of joints. Aluminium alloys with low carbon steel joints were developed using MPW for cars and ships applications without fusion welding defects. Keywords: Magnetic Pulse Welding, Dissimilar Joint, (RSM) Response Surface Methodology, Tensile Shear-Fracture Load

Microstructural evolution and fracture behaviour of dissimilar Al/Steel lap joints by laser beam oscillating welding

ABSTRACT The hybrid metal joining of aluminium alloy and steel has become the most intensively used candidate material for energy conservation and emission reduction in the automotive industry because of the comprehensive properties of low density, high strength and good corrosion resistance. In this work, experimental investigations were conducted on the laser beam oscillation welding of galvanised steel and aluminium alloy arranged in a lap configuration. Well-formed joints were successfully obtained with the aid of beam oscillating. Zigzag structures were observed at the interfacial area of Al–Fe joints instead of blocky structures due to the oscillation-driven effect of the beam. The stirring effect of the oscillating beam can promote the migration of the solute during the laser welding process, thus inhibiting the separation of components and decreasing the vulnerability to cracking. The interface zones of the laser-welded Al–Fe joints were principally made up of the Fe2Al5, FeAl, FeAl2, FeAl3 and Fe2Al5Zn0.4 phases. The joints welded with beam oscillation exhibited a tensile load and elongation amount of 1.07 kN and 0.775 mm, respectively, representing 115.67% of the loading capacity and 119.23% of the elongation compared to laser beam-welded joints without oscillation.

Experimentally validated numerical prediction of laser welding induced distortions of Al alloy parts for railcar body by inherent strain method combined with thermo-elastic-plastic FE model

A laser welding with wire filler feeding was developed to replace traditional arc welding process for joining aluminium alloy railcar body components. A three-dimensional (3D) thermo-elastic-plastic finite element (FE) model was applied to compute the plastic strains of weld zone in a downsized aluminium alloy plate with butt-joint, T-joint and fillet-joint configurations, respectively, combined with corresponding experimental validations. The achieved plastic strains at the weld zone were then input as inherent strain loadings into elastic structural FE model of fully sized aluminium alloy railcar body components to predict the welding induced distortion with the experimentally measured out-of-plane distortions. The experimentally validated FE model was then further applied for optimizing the inverse pre-deformation of plates to counteract the welding induced deformation, finally to mitigate the welding distortion issues.

Microstructure and abnormal mechanical properties under the coupling effect of strain and temperature for friction-stir-welded joints of Al-Mg-Si alloy

In the fields of automotive engineering and shipbuilding, friction stir welding (FSW) is utilized for joining aluminum alloy structural components. However, the nugget zone (NZ) in FSW joints often exhibits anomalous mechanical properties, consequently diminishing the stability of the welded joints. Here, an NZ was subdivided into a high-strain nugget zone (HS-NZ) and a high-temperature nugget zone (HT-NZ). The anomalous mechanical properties of the Al-Mg-Si alloy HS-NZ were systematically investigated at welding speeds of 100 mm/min and 200 mm/min and rotational speeds of 600 rpm and 900 rpm. Compared to the HT-NZ, the average grain size of the HS-NZ reduced by a maximum of 3 μm, the density of geometrically necessary dislocations (GNDs) increased by a maximum of 0.26 ×1014 m−2, and the microhardness showed a maximum increase of 15 HV. However, its shear strength is lower than that of the HT-NZ, with a maximum decrease of 15 MPa, exhibiting an abnormal mechanical performance. The increase in the "soft-oriented" grains in the HS-NZ results in more localized stress concentration between "soft-oriented" and "hard-oriented" grains during the deformation, thereby providing a reasonable explanation for the observed reduction in shear strength in HS-NZ under severe loading conditions. The increase of "soft-oriented" grains is primarily attributed to the promotion of discontinuous dynamic recrystallization (DDRX) facilitated by the coupled effects of high temperature and high strain. The constructed mathematical model also illustrated the effect of the coupled temperature and strain fields on the abnormal shear strength.

Direct spot joining of thin gauge aluminum alloy to stainless steel and joint performance in a corrosion environment

Direct joining of aluminum alloy and steel sheets offers a great potential for achieving effective structural lightweighting for transportation systems. The major challenge is how to avoid the formation of brittle intermetallic compounds (IMCs), which can be detrimental to joint load capacity and corrosion resistance. This paper presents a friction-based direct solid-state joining method for welding thin aluminum alloy (AA6061-T6) to stainless steel (316). Using a flat head friction heating tool, high quality interfacial bonding was achieved under a spot time of 20s and 1000 rpm without detrimental IMCs. The effects of an automotive-relevant corrosion environment condition on joint strengths were then examined through mechanical testing. The test results show that aluminum and stainless-steel spot joints produced by the proposed method exhibit no corrosion-induced damage or cracking nor any noticeable reduction in strengths, resulting in dominantly ductile failure mode.

Elucidation of role of carbon fibers on joining of metal to composite

Weight reduction in the various application fields has propelled to the forefront in investigations of combining metal with polymer. Different from other studies, this work focused on exploring the effect of carbon fibers on the thermal joining of metal to composite. Three plastics with different fiber contents including pure polyether-ether-ketone (PEEK), short carbon fibers reinforced PEEK (SCF/PEEK), and continuous reinforced PEEK (CF/PEEK) were chosen to join to the 6061aluminum alloy using a fiber laser. Results showed the thermal transfer was fostered along the carbon fiber orientation due to a higher thermal conductivity, decreasing the heat accumulation at the interface. However, the existence of carbon fibers also hindered the spreading of plastics on the aluminum alloy surface. This led to a smaller adhesion width and lower tensile-shear force of joints. In addition, the tensile-shear strength of joints prepared with carbon fibers was enhanced owing to lower thermal expansion coefficient, which improved the thermal shrinkage and reduced the stress concentration at the interface. Ultimately, the role of carbon fibers during laser joining of aluminum alloy to plastics was explained, clarifying the bonding mechanism of two materials.

Abnormal rapidly homogenized joining of aluminum alloys through a cross-scale diffusion

Rapidly homogenized joining has been a longstanding pursuit in the forming manufacturing of lightweight alloys structures. In this study, ultrasound energy was introduced into the joining process to accelerate cross-scale diffusion (direct grain migration rather than atomic-scale diffusion), and a homogeneous 6063Al joint was fabricated using a Zn-40Sn alloy at 360 °C in air. The network architecture joint composed entirely of α-Al grains was formed with a sandwich structure consisting of Sn@Al2O3/MgO as the grain boundary. The tensile strength of the joints was higher than that of the base metal in only a very short diffusion time (180 s). Physical effects of ultrasound in the Sn-Zn molten metal induced violent intergranular penetration, resulting in the decohesion and migration of the α-Al grains from the base metals and realizing a rapidly homogenized joining. This provides a foundation for full-strength joining of high-strength aluminum alloys with low thermal damage.

3-D FE modelling of residual stress distribution in 3003 aluminium alloy overlapped joints by ARM laser with beam oscillations

Adjustable Ring Mode (ARM) laser technology combined with Beam Oscillation optics module was introduced to effectively enhance weld quality in joining aluminium alloys. This study developed a three-dimensional (3-D) thermo-mechanical finite element (FE) model to analyze the distribution of thermally induced residual stresses in laser-welded 3003 aluminium alloy. The accuracy of model was validated through comparisons with experimental weld cross-sections and further reinforced by X-ray diffraction residual stress measurements. The transient temperature field and stress distribution during the welding process were investigated using the verified model. Additionally, the hardness and microstructure of the welded samples were examined through micro-hardness tests and scanning electron microscopy. Results showed that welding with beam oscillation resulted in less penetration but higher hardness and finer columnar grain size in the fusion zone. Additionally, the influence of varying standoff distances between two sequential weld beads on residual stress distribution was investigated. Numerical findings revealed that higher residual stress concentrations were located at the weld seam and dominated by tensile longitudinal residual stress and compressive transverse residual stress. As the distance between weld beads increased, transverse and equivalent residual stresses decreased, while longitudinal residual stress away from the bead increased.

Modeling and simulation of friction stir welding process: A neural approach

Friction Stir Welding (FSW) stands out as a groundbreaking method in solid-state joining for aluminum alloys, presenting an innovative way to achieve joints of exceptional quality. This research delves into the application of FSW for bonding, focusing on plates that are 6mm thick and made from aluminum alloys Al6063, Al5083, and AL6061, aiming to produce a variety of FSW joints. To evaluate the quality of these joints, the study compares mechanical properties such as tensile strength, safe bending strength, and bending toughness necessary for achieving a 90° bend. The investigation leverages welding data to formulate a neural model, starting with using a conventional feedforward neural model (CFNM). It tackles the limitations of CFNM, including its intensive training requirements and the challenge of dealing with unknown configurations, by proposing a new, more adaptable neural network model known as FNNM. When comparing the two models, it becomes evident that CFNM is constrained by a root mean square error (RMSE) of 7-15%, whereas FNNM marks a significant improvement with a minimal RMSE of 1-3%. This indicates that FNNM improves accuracy and effectively navigates the complexities of modeling with unknown parameters. Through this study, insightful contributions are made to understanding FSW in joining aluminum alloys and developing an advanced neural model capable of predicting the outcomes of welding with greater precision.

Physio-Mechanical Properties and Microstructural Characteristics of Friction Stir Welded Aluminium and Copper Plates Using Conical Unthreaded Tool

Friction Stir Welding (FSW) is a type of welding used to join materials for high strength applications. FSW is a well-liked solid-state welding technique for joining aluminum alloys and other non-ferrous materials in the aerospace, automotive, and marine industries. Pure copper and aluminum from the 6082 series were welded together using a specially designed milling machine. Tests for hardness, flexural rigidity, and impact are performed to assess the welding strength. Material flow and weld defects have been investigated by analyzing the microstructure of the weld junction. The modified vertical milling machine has been used to execute FSW of pure copper and aluminum plates. The aim is to explore the produced welded joints and to comprehend the difficulties encountered while utilizing milling machines as a FSW equipment. Similarly, to optimize the welding parameters in order to accomplish sound welding. FSW can be carried out on a milling machine because the flexural strength of a conical unthread thread tool is 108.58N/mm2 and 92.16N/mm2, respectively, at rotational speeds of 500 rpm and 1000 rpm with welding feed rates of 16 mm/min and 50 mm/min.

Research Progress of Aluminum Alloy Welding/Plastic Deformation Composite Forming Technology in Achieving High-Strength Joints.

Fusion welding causes joint deterioration when joining aluminum alloys, which limits the use of aluminum alloy components in high-end equipment. This paper focuses on an overview of how to achieve high-strength aluminum alloy welded joints using welding/plastic deformation composite forming technology. The current technology is summarized into two categories: plastic deformation welding and plastic deformation strengthening. Plastic deformation welding includes friction stir welding, friction welding, diffusion welding, superplastic solid-state welding, explosive welding, and electromagnetic pulse welding. Plastic deformation strengthening refers to the application of plastic deformation to the weld seam or heat-affected zone, or even the whole joint, after welding or during welding, including physical surface modification and large-scale plastic deformation technology. Important processing parameters of plastic deformation welding and their effects on weld quality are discussed, and the microstructure is described. The effect of plastic deformation strengthening technology on the microstructure and performance evolution, including the hardness, tensile strength, fatigue property, residual stress, and hot cracking of aluminum alloy welded joints, and its evolution mechanism are systematically analyzed. Finally, this paper discusses the future development of plastic deformation strengthening technology and anticipates growing interest in this research area.

Joining Aluminum Alloy and Steel by Friction Stir Forming from Steel Side

A technique for fabricating structural joints by closed-die-type friction-stir forming (FSF) is introduced in this study. The process is as follows. First, a steel sheet with a prepared hole is placed on an aluminum alloy plate. A die with a through-hole cavity is then placed above it to press down the steel sheet tightly. Next, a rotating stepped cylindrical tool is inserted into the through-hole cavity. To enclose the die cavity, the upper side of the tool is then positioned such that it is nearly in full contact with the inner surface of the through-hole. Finally, the top part of the tool is allowed to penetrate into the aluminum alloy plate through the prepared hole of the steel sheet to cause the material to extrude backward. Consequently, the material fills the whole of the space between the tool and die to generate a hollow-rivet-like aluminum alloy structure fastening the steel sheet to the aluminum alloy plate. This technique enables easier alignment between the die and the prepared hole of the steel as compared with the conventional joining technique which uses FSF. In addition, the new technique uses a one-sided approach (i.e., from the side of the harder material with a higher melting temperature) to join dissimilar materials, a process which is difficult for conventional methods of friction-stir welding and forming.