EN AW Research Articles

Analysis of the Effect of Surface Preparation of Aluminum Alloy Sheets on the Load-Bearing Capacity and Failure Energy of an Epoxy-Bonded Adhesive Joint.

Surface preparation is an important step in adhesive technology. A variety of abrasive, chemical, or concentrated energy source treatments are used. The effects of these treatments vary due to the variety of factors affecting the final strength of bonded joints. This paper presents the results of an experimental study conducted to determine the feasibility of using fiber laser surface treatments in place of technologically and environmentally cumbersome methods. The effect of surface modification was studied on three materials: aluminum EN AW-1050A and aluminum alloys EN AW-2024 and EN AW-5083. For comparison purposes, joints were made with sandblasted and laser-textured surfaces and those rolled as reference samples for the selected overlap variant, glued with epoxy adhesive. The joints were made with an overlap of 8, 10, 12.5, 14, and 16 mm, and these tests made it possible to demonstrate laser processing as a useful technique to reduce the size of the overlap and achieve even higher load-bearing capacity of the joint compared to sandblasting. A comparative analysis was also carried out for the failure force of the adhesive bond and the failure energy. The results show the efficiency and desirability of using lasers in bonding, allowing us to reduce harmful technologies and reduce the weight of the bonded structure.

Fundamental investigation on the time-variance of process stability

Disturbance factors, such as self-excited tool vibrations, limit the performance of modern machining processes and thus restrict the quality, productivity and sustainability of industrially manufactured components. The dynamic process stability is subjected to significant variances especially at the beginning of the tool life. To precisely quantify these variances, series of milling tests were conducted and analyzed using tools made of high speed steel (HSS) and cemented carbide for the machining of EN AW-7075. In all test series, a critical initial decrease of the stability limit was detected directly at the beginning of the tool life. In the following, a significant increase and subsequent almost constant stability limit was observed. In the case of the HSS cutters the achieved stability limit exceeded the initial level substantially. An increase in the process forces and flank wear was also measured over tool life but the progression cannot directly explain the extend and characteristics regarding the stability limit. The findings described have a considerable impact on the appropriate design of manufacturing processes and experiments to determine the dynamic stability of cutting operations.

Characterization of Interfacial Corrosion Behavior of Hybrid Laminate EN AW-6082 ∪ CFRP.

The corrosion behavior of a hybrid laminate consisting of laser-structured aluminum EN AW-6082 ∪ carbon fiber-reinforced polymer was investigated. Specimens were corroded in aqueous NaCl electrolyte (0.1 mol/L) over a period of up to 31 days and characterized continuously by means of scanning electron and light microscopy, supplemented by energy dispersive X-ray spectroscopy. Comparative linear sweep voltammetry was employed on the first and seventh day of the corrosion experiment. The influence of different laser morphologies and production process parameters on corrosion behavior was compared. The corrosion reaction mainly arises from the aluminum component and shows distinct differences in long-term corrosion morphology between pure EN AW-6082 and the hybrid laminate. Compared to short-term investigations, a strong influence of galvanic corrosion on the interface is assumed. No distinct influences of different laser structuring and process parameters on the corrosion behavior were detected. Weight measurements suggest a continuous loss of mass attributed to the detachment of corrosion products.

The effect of partial recrystallization on the corrosion resistance of EN AW6082 forged components evaluated with different tests

AbstractStructural automotive components are extensively made of aluminum alloy forgings, due to the elevate strength and low weight required. These products are frequently subjected to recrystallization. Recrystallization, often limited to surface or forging portions, is expected to reduce its tensile strength and corrosion resistance, but the literature is scarce on this subject. For a more comprehensive understanding, the present research studied the corrosion behavior of samples collected from EN AW 6082‐T6 forged components, designed to expose both recrystallized and not recrystallized surfaces to the corrosive environment. Several standardized corrosion tests (i.e., PV 1113, ISO 11846, and VW 96380) were applied to assess the most representative with respect to real field exposure. Tensile tests were performed in four different conditions, recrystallized and not recrystallized specimens in an as‐forged state or after corrosion. The recrystallization led to a reduction in tensile properties, but this gap was compensated by a higher corrosion resistance than the not recrystallized samples. Consequently, the mechanical properties became comparable after the corrosion test.

Exploring the Potential Application of an Innovative Post-Weld Finishing Method in Butt-Welded Joints of Stainless Steels and Aluminum Alloys.

The prerequisite of the weld bead finishing is intricately linked to the quality of the welded joint. It constitutes the final, yet pivotal, stage in its formation, significantly influencing the reliability of structural components and machines. This article delineates an innovative post-weld surface finishing method, distinguished by the movement of a specialized cutting tool along a butt weld. This method stands out due to its singular approach to machining allowance, wherein the weld bead height is considered and eradicated in a single pass of the cutting tool. Test samples were made of AISI 304L, AISI 316L stainless steels and EN AW-5058 H321, EN AW-7075 T651 aluminum alloys butt-welded with TIG methods. Following the welding process, the weld bead was finished in accordance with the innovative method to flush the bead and the base metal's surface. For the quality control of welded joints before and after the weld finishing, two non-destructive testing methods were chosen: Penetrant Testing (PT) and Radiographic Testing (RT). This article provides results from the examination of 2D profile parameters and 3D stereometric characteristics of surface roughness using the optical method. Additionally, metallographic results are presented to assess changes in the microstructure, the microhardness, and the degree of hardening within the surface layer induced by the application of the innovative post-weld finishing method.

Influence of corrosion fatigue on the stress gradient effect of the aluminium alloy EN AW-6082 T6

This study investigates the influence of corrosion fatigue on the fatigue strength of the aluminium alloy EN AW-6082 T6 with regard to the stress gradient. The experimental design involves varying loading conditions and specimen geometries to facilitate testing under three distinct stress gradients: tension/compression (0mm-1), rotary bending (0.2mm-1), notched rotary bending (5.3mm-1). Reference constant loading tests in air as well as continuously irrigated corrosion fatigue tests in a 5wt% NaCl-solution are conducted with a constant stress ratio of R =−1. The results reveal a substantial reduction in fatigue strength due to corrosion fatigue across all three stress gradients. The slope of the S-N curves drops by a factor of at least two and no second slope of the S-N curves is found within the tested load cycle range (up to 107). The study demonstrates a significant increase in the support factor for tests conducted in the corrosive environment. This discrepancy becomes more pronounced towards higher stress gradients and lower load cycle numbers. The application of the support factor derived from tests in a non-corrosive atmosphere is shown to be conservative, emphasizing the significance of accounting for corrosion effects in assessing fatigue behaviour.

Exfoliation behavior of EN AW 7020 with T6, step aging and ultrasonic impact peening processes

Abstract In this study the effect of T6 heat treatment, two-step aging treatment and ultrasonic impact peening on the exfoliation corrosion behavior of welded EN AW 7020 was investigated. Exfoliation tests were performed according to the ASTM G34-01 standard. As expected, as a result of the tests, the base material region of all three samples were showed better corrosion resistance than the heat-affected region. Ultrasonic impact peening and two-step aging treatment was observed that improved EXCO sensitivity in the weld area. When sorting was made by considering the resistance to corrosion of the heat affected zone of the samples, it was observed that the best resistance was shown by the sample with two-step aging treatment, and the worst resistance was shown by the sample with T6 heat treatment.

Dissimilar friction stir welding and post-weld heat treatment of Ti-6Al-4V and AA7075 producing joints of unprecedented strength

Dissimilar welding of Ti and Al alloys is challenging due to the potential formation of brittle intermetallics, which can compromise weld strength. Friction stir welding (FSW) is an advanced joining method with the potential to drastically reduce or prevent the formation of intermetallic phases because melting is avoided. However, in previous studies, dissimilar joints of Ti-6Al-4V and EN AW-7075 with satisfactory strength could not be achieved. Thus, we investigated friction stir welding of these two materials in a butt configuration, and analyzed the effects of post-weld heat treatments on the mechanical properties. Tensile strengths of 441 MPa in the as-welded condition and 505 MPa after heat treatment were achieved, significantly surpassing strength values reported in earlier studies. Microscopic investigations showed no evidence of formation of brittle intermetallic phases, and ductile fracture was observed. Our results show that FSW is a very promising candidate for future aerospace applications requiring dissimilar joining of Ti and Al alloys.

Effect of the Technological Parameters of Milling on Residual Stress in the Surface Layer of Thin-Walled Plates.

The production of thin-walled elements, especially those with large overall dimensions, poses numerous technological and operational problems. One of these problems relates to the machining-induced strain of such elements resulting from residual stress generated during the machining process. This study investigates the effect of the technological parameters of milling on residual stress in the surface layer of thin-walled plates made of aluminum alloy EN AW-2024 T351 for aerospace applications. The results have shown that residual stress increases with the cutting speed only to a certain point, reaching the maximum value at vc = 750 m/min. At a cutting speed vc = 900 m/min, residual stress significantly decreases, which probably results from the fact that the milling process has entered the High-Speed Cutting range, and this inference agrees with the results obtained for the cutting force component. Residual stress increases with the feed per tooth, while the relationship between residual stress and milling width is the same as that established for residual stress and variable cutting speed. Positive tensile stress is obtained in every tested case of the milling process. The results have also shown that the induced residual stress affects the strain of machined thin-walled parts, as proved by the strain results obtained for milled thin walls.

Single-step self-punching lockbolt process for aluminum sheets without pre-hole

For the mechanical joining of aviation-grade aluminum alloys, the study introduces an innovative approach using self-punching lockbolts. This method involves the utilization of a profiled collar and a specially designed bolt to seamlessly join EN AW-2024 T42 aluminum sheets, up to a thickness of 8.0 mm, without the need for pre-holes. In this process, when the aluminum sheets are punched, the collar undergoes slight deformation, effectively functioning as a die. Subsequently, the collar is systematically formed by applying increased force. By fine-tuning the design of the bolt ring groove, it becomes feasible to create a joint with a bolt length that accommodates sheet thickness variations of up to 1.6 mm. To facilitate this development, the joining process was meticulously designed and the auxiliary part was optimized with the aid of numeric simulation tools. The process simulation enabled the identification of deformation mechanisms within the collar, accounting for both geometry and material properties. The important factors influencing collar deformation include collar thickness, shoulder height, and shoulder diameter. Furthermore, experimental investigations were conducted to assess the mechanical properties of the joint and evaluate how material-specific factors influence joint failure behavior. It can be seen that the formation of the mechanical fit is influenced by the ring groove depth and the fitting position. The joints failed under shear tensile load exclusively at the bolt head.

New Method for Detecting Flange Fracture Initiation in Incremental Radial Extrusion.

This study investigates flange fracture formation in unconventional incremental radial extrusion. This manufacturing technique involves using rings with a gradually increasing inside diameter for constraining the free flow of material in the radial direction. As a result, the shaped flange has a constant thickness and a significantly larger diameter than that formed using the standard extrusion process conducted without the use of rings. EN AW 6060 aluminum alloy tube sections were used as the billet material, and the extrusion process was conducted under cold forming conditions at ambient temperature. For the determination of material fracture initiation, a new method was proposed involving the analysis of strain, strain rate and values of the normalized Cockcroft-Latham fracture criterion integral. The main advantage of the new method is that it allows for the prediction of fracture initiation via only FEM results analysis, i.e., it is not necessary to carry out additional experiments aimed at calibrating or determining limit parameters of a given material. It was shown that the occurrence of differences in the distribution of the above-mentioned parameters coincided with flange fracture initiation.

Hybrid Joining of Dissimilar Thin Metallic Sheets—Mechanical Joining and Adhesive Bonding

This paper deals with joining dissimilar materials using thermal drilling technology as well as the combination of thermal drilling and adhesive bonding. The base materials for the experimental work were deep-drawn low-carbon steel DC04, HSLA steel TL 1550-220 + Z, and structural aluminum alloy EN AW-6082 T6 (AlSi1MgMn). The geometry of the formed joints was tested metallographically as the load-bearing shear capacity under the tensile shear test of single-lapped joints and the resistance of the joints against corrosion-induced disbonding in a climate chamber. The energy dissipated by the joints up to fracture was calculated from the load–displacement curves. The hybrid joints were compared with the bonded joints with the same overlap area in terms of the load-bearing capacity and energy dissipated at joint failure. The hybrid joints formed by thermal drilling and adhesive bonding with a rubber-based adhesive confirmed the synergistic effect—the adhesive provides the high load-bearing capacity of the joint, and the bushing formed by thermal drilling increases the dissipated energy of the joint at failure. The exposure of the joints in the climatic chamber did not cause a relevant reduction in the characteristics of the joints.

Cold Rolling Technology Optimization for EN AW 4343/3003/4343 Cladded Aluminum Alloys and Influence of Parameters on Microstructure, Mechanical Properties and Sustainable Recyclability

The present study investigates the accumulative roll bonding process applied to the EN AW 3003 aluminum alloy, serving as a composite material on both sides and consisting of the EN AW 4343 aluminum alloy. For the characterization of the optical microscopy, corrosion tests with saltwater acetic acid and mechanical properties before and after the braze test were employed. The numerical simulations accurately predicted the industrial cold rolling values for the rolling force and surface temperature. The most comprehensive understanding of the cold rolling parameters for both side-cladded materials was achieved by combining predictions for cladded and uncladded materials. The thickness of the cladded layer presented as a percentage after roll bonding was 18.7%. During the cold rolling and annealing, the cladded thickness was increased to 24.7% of the final 0.3 mm of the total cold-rolled product thickness. According to the performed braze test for final thickness, the ultimate tensile strength and yield strength were decreased, and the elongation increased to 18.1%. In addition to the described changes in mechanical properties, the material’s anisotropy improved from 5.4% in the cold-rolled condition to 2.0% after the braze test. After multiple re-meltings of the cladded material, the analyzed chemical compositions allow for recycling and reuse as different 4xxx, 5xxx, and 6xxx alloys.

Fretting fatigue of cast iron and aluminium – A strength assessment method based on a worst-case assumption

Many components made of cast iron (e.g., in combustion engines) and aluminium (e.g., in aircraft construction) are subject to fretting fatigue. This results in a need for a method for assessing the strengths of the aforementioned materials that takes into account the reduction in fatigue strength due to fretting as well as the accompanying reduction in service life. In a first paper, the authors already presented a calculation method for the fail-safe design of steel–steel contacts subject to fretting fatigue. This enables the engineer or designer to perform a strength assessment for any component connection made of steel. The calculation method is based on a tribological worst-case assumption and can be integrated into the analytical strength assessment of the internationally known FKM Guideline. The strength reduction is taken into account by use of empirically determined fretting factors. The frequent failures of component connections made of cast iron and aluminium in the field made an extension of the calculation method became necessary. This work therefore includes experimental investigations into the materials EN-GJS-700, EN-GJS-400 and EN-GJL-300 (cast iron), as well as EN AW-7075 T651, EN AW-6082 T651 and EN AW-5083 (aluminium). Since the main parameters determining fretting fatigue strength are slip amplitude and contact pressure, the worst-case combinations of these parameters (resulting in the lowest friction fatigue strength) were first determined for each of the two material groups using a laboratory test setup. These parameters could be found at sa=10μm;p=40MPa for cast iron and sa=5μm;p=10MPa for aluminium. Based on these worst-cases, the fretting fatigue limits of the aforementioned materials were determined, as well as the effect of mean stress. The fretting factors of the materials were derived from the experimental results. Additional experimental investigations using a connecting-rod-like geometry served to validate an application typical of the industry. Using the calculation method, the degree of utilisation of the connecting rods could be determined with good accuracy (maximum error: 18.7%).

Creation of an Aluminum Alloy Template with a Surface Structure by Micro-Milling for Subsequent Replication of the Microstructure to Achieve Hydrophobicity

This research paper focuses on the fabrication of a microstructure based on a natural structure pattern of hydrophobic properties using micro-milling technology, followed by an investigation of the dimensional accuracy, roughness, and replication of the fabricated microstructure. Design, modeling (CAD system), fabrication, and replication are the steps of this process. Knowledge of biomimetics was used to select the microstructure. The main research aim of the experiments is to verify and extend the applicability of conventional CNC manufacturing technologies to obtain a functional surface structure. The micro-milling was carried out on a conventional DMG MORI CNC machine, a CMX 600 V three-axis horizontal milling center, using an external high-frequency electric spindle clamped to the machine. The machined material was aluminum alloy EN AW 7075. The tool was a 0.1 mm diameter double-edged ball mill made of sintered carbide and coated with TiSiN. The cutting conditions were determined according to the tool manufacturer’s recommendations. To compare the achieved accuracies, the same microstructure was fabricated using PLA technology. For subsequent replication of the sample, the negative of the selected microstructure was created and machined. Subsequently, a positive microstructure was created using the silicone impression material by the replication process. This paper and the experiments performed extend the technical knowledge in the field of manufacturing surface functional structures and confirm the possibility of manufacturing the designed structures using chip and laser machining technology, with achieved discontinuities in the range of 3 to 50 μm. They also highlight the issues of replication of such structures with respect to critical manufacturing locations (geometrical parameters of the structures affecting the functional properties of the structure, venting, replica defects, etc.).

Development of FSW Process Parameters for Lap Joints Made of Thin 7075 Aluminum Alloy Sheets.

The article describes machine learning using artificial neural networks (ANNs) to develop the parameters of the friction stir welding (FSW) process for three types of aluminum joints (EN AW 7075). The ANNs were built using a total of 608 experimental data. Two types of networks were built. The first one was used to classify good/bad joints with MLP 7-19-2 topology (one input layer with 7 neurons, one hidden layer with 19 neurons, and one output layer with 2 neurons), and the second one was used to regress the tensile load-bearing capacity with MLP 7-19-1 topology (one input layer with 7 neurons, one hidden layer with 19 neurons, and one output layer with 1 neuron). FSW parameters, such as rotational speed, welding speed, and joint and tool geometry, were used as input data for ANN training. The quality of the FSW joint was assessed in terms of microstructure and mechanical properties based on a case study. The usefulness of both trained neural networks has been demonstrated. The quality of the validation set for the regression network was approximately 93.6%, while the errors for the confusion matrix of the test set never exceeded 6%. Only 184 epochs were needed to train the regression network. The quality of the validation set was approximately 87.1%. Predictive maps were developed and presented in the work, allowing for the selection of optimal parameters of the FSW process for three types of joints.

The effect of temperature on the transfer layer of an aluminium alloy on tool steel and the effect of CrN coating

It is essential to explore temperature's crucial role while unveiling the intricacies of tribological interplay in CrN-coated steel-alloy systems. In the present study, tribological potential of CrN-coated hot-work tool steel was investigated under unidirectional single-pass sliding wear conditions. The sliding wear tests were performed at different temperatures (i.e., 20 °C, 100 °C, 200 °C, 300 °C, 400 °C and 500 °C) for the different sliding distances between 2 mm and 68 mm to explore the effect of temperature on the initiation and evolution of the transfer of an aluminium alloy (EN AW-6060). The effect was studied in terms of the contact area of the aluminium alloy and the volume transferred to the surface of the CrN. In addition, the structure of the wear trace and the equivalent friction coefficient were monitored with respect to the sliding distance and the temperature. The results show the strong dependency of the tribological potential of the CrN coating and the aluminium alloy on the temperature but show insignificant dependency on the sliding distance. When sliding up to 200 °C, the transfer was found to be dependent on the surface roughness of the coating, while strong adhesion led to the aluminium alloy's transfer during sliding at higher temperatures, that is, above 300 °C. At 500 °C, the CrN coating formed a self-protective Cr2O3 oxide that reduced the adhesive transfer of the alloy to the CrN compared to that at 200 °C–300 °C.

Optical strain measurements during pulsed laser beam welding to improve the understanding of hot crack formation of EN AW-6082 aluminum alloy

E-mobility turned in the last years to be an emerging market and one solution to fossil fuel free mobility for the future. E-mobility requires, compared to fossil-fueled mobility concepts, a huge amount of welding tasks, which have to guarantee different functionality, as for example high strength, ductility, but also low resistivity and tightness. Last is especially for housing or cases of aluminum in automotive challenging, as pores and cracks can occur. Pulsed laser welding presents, due to the adaptable heat input and the temporal modification of stress state and solidification conditions advantages for this type of applications. EN AW-6xxx group of aluminum alloys is mainly used for such components due to their favorable mechanical properties. However, these alloys are susceptible to hot cracking during solidification from the molten phase. This article aims to present a methodology for demonstrating the resulting strain during pulsed laser beam welding of hot crack susceptible aluminum alloys. It will highlight the influence of factors such as pulse shape, shielding gas, and flow rate on strain and strain rate.

Surface microstructuring by Ultrasonic Vibration Assisted Deformational Machining (UVADM) – Simulation and experimental results

Polymer-metal hybrids are a lightweight solution for many industrial applications, especially in the automotive or aircraft sector. However, due to their poor chemical bonding the manufacturing of such compounds requires the use of adhesive layers or the conditioning of the metallic surface to achieve form closure and high joint strength. Ultrasonic Vibration Assisted Deformational Machining (UVADM) is a novel process that generates functional microstructures with high production rates, aiming to form defined burr structures with undercuts, that have a significant impact on the interlaminar strength of polymer-metal hybrids (PMH). A 3D FEM simulation using Abaqus/Explicit software was applied to design and analyze process conditions including tool geometry. Material deformation was described by the Johnson-Cook model. Simulation results were validated experimentally using two different MCD tools. For the UVADM experiments, specimens of the aluminum alloy EN AW-6082 were used. In the tests, a constant ultrasonic frequency (20.42 kHz), machining speed (100 m/min and 200 m/min), and peak-to-peak amplitude (7 µm) were used. Geometrical surface properties were analyzed by optical methods and SEM. The study demonstrates a conformity between simulated and experimental results, highlighting the potential of UVADM for an increased productivity in the surface conditioning for polymer-metal hybrids.

Comparison of 2D and 3D measurement methods for evaluating laser structured aluminum surfaces using fractal dimension

The interlaminar strength of mechanically interlocked polymer-metal hybrids is strongly determined by the surface geometry at the interface. To improve the interlaminar strength, laser beam machining is among the most applied technologies for manufacturing a predefined and complex surface structure. Previously, the fractal dimension of interfaces in polymer-metal-hybrids has been introduced as scale-independent measure. It has been correlated quantitatively with the interlaminar strength using values derived from cross-sectional images. Therefore, the quality of the prediction directly depends on the accuracy of the measured surface data. However, a holistic acquisition of surface structure for the determination of the fractal dimension including 3D methods has not been investigated so far. In this study, laser machining was used to generate five different pin-structures on samples of the aluminum alloy EN AW-6082. Surface characterization was realized by light microscopy (2D), laser scanning microscopy (3D) and X-ray microscopy (3D). Subsequently, the fractal dimension was determined using a box-counting algorithm as well as slit-island method. The results show that all methods regarded are appropriate to determine the fractal dimension, but differ in the specific results. The functional characteristics of each method are described in detail and potentials for applications are outlined.