EN AW Research Articles

Simulation-Assisted Process Design and Experimental Verification of Laterally Confined Oxide Areas Generated with Continuous Electrolytic Free Jet on EN AW-7075 Aluminum Alloy

Local anodization with a free electrolyte jet is a suitable solution for locally confined surface functionalization without additionally required preparation of the parts. However, the geometrical formation of the anodic oxide layer in jet-based anodization is not yet sufficiently understood. In this study, numerical calculations based on physical descriptions are used to describe the lateral and vertical oxide formation on aluminum alloy EN AW-7075. The required electrical resistance and capacitance were determined by immersion-based anodization and implemented into the numerical simulation model to evaluate the electrical conductivity of the porous layer. The simulation results showed an electrical conductivity of 2.6 × 10-6 S/m for the porous layer. Subsequently, a model for jet-based anodization was developed and the previous results were implemented to calculate the oxide formation. The simulation results showed decreasing oxide layer thickness at increasing radial distance from the center of the jet, which corresponds to experimental results. The simulation model was validated by varying the current efficiency from 5% to 90%, where similar developments of the anodic oxide layer thickness compared with experimental results were determined at 5%.

Effect of Diamond Burnishing on the Properties of FSW Joints of EN AW-2024 Aluminum Alloys

The article presents the results of an analysis of the surface roughness parameters, microhardness, and the stresses of the surface layer ofFSW butt joints subjected to the burnishing process with a diamond tip. This can be useful in selecting the optimal parameters of the burnishing process, ensuring the best properties of the surface layer of the FSW joint. Burnishing force and feed rate influence were analyzed according to the two-factor three-level full factorial statistical completed plan PS/DC 32. The tested material was 2024-T3 aluminum alloy sheets with a thickness of 2 mm. The results show that burnishing significantly reduced the surface roughness from Sa = 6.46 μm to Sa in the range of 0.33 μm–1.7 μm. This treatment provides high compressive residual stresses σx from −86 to −130 MPa and σy from −158 to −242 MPa. Microhardness increased from 84.19% to 174.53% compared to butt joints. Based on the obtained results, multi-criteria optimization was carried out. This optimization allows us to obtain a compromise solution ensuring compressive stresses in the surface layer (σx=−123 MPa and σy=−202 MPa) and microhardness HV=362.56 mm/mm2 with the roughness of the weld surface Sa = 0.28 µm, Sku = 3.93 and Spc = 35.88 1/mm.

Fatigue life improvement of similar and dissimilar aluminum friction stir welds by deep rolling

At the moment, high production costs prevent the friction stir welding (FSW) process from further industrial applications even if comparable high fatigue strength of the joints can be reached. Higher welding speed may reduce the production costs but decrease the fatigue strength of the manufactured FSW joints. A potential solution is a mechanical post weld treatment directly after welding to increase the fatigue strength of the FSW joint again. In this study, hydrostatic deep rolling was applied for fatigue strength improvement of similar and dissimilar FSW joints made of EN AW 5083 and EN AW 6082 alloys manufactured with different welding speed. Additionally, the fatigue strength was directly compared to conventional joints manufactured by metal inert gas (MIG) welding and to base material specimen made of EN AW 5083. The surface state in as-welded condition was characterized by surface roughness and residual stress measurements. Fatigue tests were performed to quantify the fatigue strength of the FSW joints. Similar compressive residual stresses were determined after deep rolling for similar and dissimilar joints. No fatigue life improvement was determined for deep-rolled similar joints made of EN AW 5083. However, in this condition, the fatigue life of the specimen was within the range of the base material. Thus, significant lower fatigue life and a high fatigue life improvement by deep rolling were reached for dissimilar joints. An increase of the welding speed from 300 to 800 mm/min strongly decreased the fatigue strength of dissimilar welded joints in the investigated case.

Pin-Shaped Surface Structures Generated by Laser Single Pulse Drilling for High-Strength Interfaces in Thermally Joined Polymer-Metal Hybrids.

Laser structuring is by far the most investigated metal surface-pretreatment method for creating adhesion in polymer-metal hybrids. Especially, cone-like protrusions show excellent wetting behaviour as well as high compound strength. However, the processing time is extremely high. Therefore, this paper assesses a process strategy for creating pin structures with scalable height by single pulse drilling with an Nd/YVO4 nanosecond laser system on EN AW-6082 aluminium alloy. The strength testing is carried out by butt-bonded hollow cylinder torsion. The samples are manufactured by heat-conduction thermal joining with polyamide 6. Ten different surface structures with two different ablation diameters are investigated and compared to cone-like protrusions in terms of processing time, wetting behaviour, shear strength and fracture behaviour. The experimental results show that pulse drilling pins structures with high aspect ratio reach-strength values close to cone-like protrusions but with 31 times higher processing rate.

Effect of Weld Length on Strength, Fatigue Behaviour and Microstructure of Intersecting Stitch-Friction Stir Welded AA 6016-T4 Sheets.

Friction stir welding is a promising joining process for boosting lightweight construction in the industrial and automotive sector by enabling the weldability of high-strength aluminum alloys. However, the high process forces usually result in large and heavy equipment for this joining method, which conflicts with flexible application. In order to circumvent this issue, a friction stir welding gun has been developed which is capable of producing short stitch welds-either stand-alone as an alternative to spot welds or merging into each other appearing like a conventional friction stir weld. In this study, the influence of the stitch seam length on the strength properties of intersecting friction stir welds is investigated, and the weld is characterized. For this purpose, EN AW-6016 T4 sheets were welded in butt joint configuration with varying stitch lengths between 2 and 15 mm. Both the static and dynamic strength properties were investigated, and hardness and temperature measurements were carried out. The results show a scalability of the tensile strength as well as the fatigue strength over the stitch seam length, while the substitute proof strength is not affected. Hereby, the tensile strength reached up 80% of the base materials tensile strength with the chosen parameter setup. Likewise, the stitch weld length influences the hardness characteristics of the welds in the transition area.

Citric Acid As an Eco-Friendly Inhibitor for Aluminum Alloy EN AW-2024 Corrosion in Acidic Medium

Citric Acid As an Eco-Friendly Inhibitor for Aluminum Alloy EN AW-2024 Corrosion in Acidic Medium

Determining material model parameters by optimization for temperature controlled friction stir additive manufacturing

Friction stir additive manufacturing (FSAM) is a novel process with the potential of being used for efficiently fabricating large aircraft structures. It is based on the repeated stacking and friction stir lap welding of metal sheets. Recent studies have reported that temperature-related defects occur in the upper layers of the builds, which are explained by changed thermal conditions. The temperatures during fabrication can be calculated by a digital twin of the process. A precise material model is necessary for this purpose. This paper presents and discusses several strategies used to determine Johnson-Cook material model parameters for the aerospace aluminum alloy EN AW-7075. Using only the process data of two welding experiments, suitable material model parameters (C of -0.14161, m of 0.66863) were determined by solving an optimization problem. For these parameters, the mean absolute temperature error was less than or equal to 4.07 K for unknown test data. The method therefore enables the inline calculation and control of the welding temperature during FSAM, thus ensuring stable thermal conditions and high-quality parts.

Numerical investigation of thermal buckling and post-buckling behavior of an EN AW 6016-T4 car roof assembled in a steel body-in-white

The automotive industry is undergoing significant changes driven by factors such as reducing carbon dioxide emissions, advancing technology, evolving regulations, and the emergence of new energy sources. Lightweight materials, particularly aluminum alloys, are being extensively researched and integrated into vehicles to reduce weight and improve performance. However, the heating process during vehicle production can cause thermal buckling in thin aluminum alloy structures, affecting their appearance and quality. While thermal buckling has been studied in other industries, research in the automotive sector, particularly for non-structural parts like car roofs, is limited. This study uses numerical simulation to predict thermal buckling and post-buckling behavior of a EN AW 6016-T4 alloy car roof assembled in a predominantly steel body-in-white. The research findings indicate that roof buckling occurs at a relatively low temperature difference of approximately 60 °C, which is lower than the maximum temperatures experienced during the painting phases in the automotive industry. Consequently, undulations in the roof's shape become apparent, underscoring the importance of design modifications to ensure visual conformity. Validation through physical testing confirms the model's accuracy, providing valuable insights for designing lightweight structures with improved performance and aesthetics.

Assessment of the impact of process parameters on the final material properties in forming of EN AW 7075 employing a simulated forming process

The impacts of various thermo-mechanical process routes in forming of EN AW 7075 alloy on mechanical properties, microstructure and corrosion resistance were investigated. A simulated forming process of two very different conditions, i.e., T6 and W-Temper is the focus of the present study. Irrespective of soaking time and pre-deformation, specimens quenched in water exhibited superior mechanical properties compared to air-cooled ones. A shorter solution heat-treatment soaking time in the pre-deformed condition, i.e., T6-Temper, caused a drop in the elongation at fracture. Microstructural analysis revealed, regardless of pre-deformation and soaking time, a high fraction of fine η′ strengthening precipitates with stoichiometry close to MgZn upon artificial ageing in the specimens quenched in water. Mechanical properties and microstructural evolution indicate that pre-deformation of solution heat treated specimens before the ageing treatment, i.e., W-Temper, leads to dislocation multiplication and, eventually, further nucleation sites for precipitation. Thus, forming the W-Temper condition caused very similar resulting mechanical properties and microstructure compared to that of the T6 condition. However, W-Temper forming was found to be detrimental for stress corrosion cracking. Corrosion behaviour of air-cooled specimens was found to be very poor in general. Results obtained in the present work can facilitate the development of thermo-mechanical process routes for EN AW 7075 to eventually tailor mechanical properties, corrosion behaviour and microstructure.

Dependency of mechanical properties on artificial aging conditions for EN AW 6082 aluminum alloy

Aluminum 6xxx series alloys attract attention owing to their decent strength, formability and corrosion characteristics. Mechanical properties of these alloys can be altered via precipitation hardening by applying an aging treatment known as artificial aging (AA). This investigation was focused on the behavior of mechanical properties of EN AW 6082 alloy for various aging conditions. Mechanical property response for different heat treatment procedures were analyzed together with DSC results and TEM micrographs. Solution heat treatment (SHT) temperature was found to affect the obtained yield strengths after AA considerably and higher SHT temperatures lead to higher yield strength for same artificial aging condition. It was also shown that yield strength values obtained after 480 min—180 °C artificial aging can be surpassed in shorter times at higher artificial aging temperatures. Aging times as short as 60 min may be employed using temperatures above 200 °C to obtain higher strength than 480 min—180 °C aging. Linear relationships between Vickers hardness and mechanical strengths were suggested for the complete data of the study. Negative effects of over-aging on ductility were presented and β′′ precipitates which are responsible for hardening during aging were presented using TEM micrographs. Additionally, high cycle fatigue tests were conducted for AA procedures 480 min—180 °C and 240 min—200 °C and similar fatigue strengths were reported.

Numerical analysis of burst pressure and maximum inflation height of aluminium made pillow plates

Pillow plates represent an efficient type of heat transfer equipment with a high degree of flexibility in terms of manufacturing and applications. Their thermo-hydraulic behaviour has been the focus of numerous scientific investigations over the last decade. However, along with the realisation of the thermal task, it is also important to ensure an adequate level of operational safety when designing equipment based on pillow plates. At present, for the approval of a pillow plate based apparatus, an experimental proof of the permitted operating pressure must be provided in accordance with the regulatory standards. In this process, this pressure is calculated from the burst pressure, which must be determined in time-consuming and cost-intensive experiments. For this reason, we propose a new approach in which the burst pressure of pillow plates is determined numerically based on the finite element methods, eliminating the need for experiments. Furthermore, the simulation results were used to derive equations for calculating the burst pressure and the maximum achievable inflation height of pillow plates made of the aluminium alloy EN AW- 5083. This part of the work has been motivated by the findings of a preliminary study showing a more than 25% thermal resistance reduction of counterflow operated pillow plate heat exchangers when the pillow plates are made of aluminium instead of the standard material stainless steel.

Investigations on design limits and improved material utilization of press-fit connections using elastic-plastic design

Today, there are a number of analytical and numerical calculation methods for the elastic-plastic design of press-fit connections. However, these are largely constrained by their restriction to elastic-ideal-plastic material behavior. In addition, recommendations for limiting the plasticized hub cross section that have been provided to date do not exploit the full potential of the materials, with the result that opportunities for lightweight design and improved transmission capacity have remained unused so far. Yet, no experimental validations exist to this end, which is why the existing design method could not be validated until today. In addition, there is still a lack of research on how to evaluate the potential for increasing the force and torque transmission under consideration of the strain hardening of the material during plastic deformation. The lack of knowledge today prevents a targeted design and thereby the industrial application of this type of connection; the transmission capacity and lightweight design potentials have thus remained unused until now (Kröger and Binz, 2020). This article presents the actual design and joining limits of hubs made of EN AW-5083 (AlMg4,5Mn), which were determined as part of an Industrial Collective Research (IGF) project. This allows the hub materials to be better utilized, which leads to a reduction in mass and/or an increase in the force and torque transmission. In addition, the experimental validation of the numerical investigations helps to establish the design method in industrial practice.

THE EFFECT OF COOLING METHOD ON SURFACE ROUGHNESS IN DEEP HOLE DRILLING OF ALUMINIUM ALLOYS

This paper presents the results of an experimental study investigating the effect of usage of different cooling methods in drilling of aluminum alloys with different surface roughness properties of these materials. Two alloys were tested: EN AW2024 and AlSi10Mg with a high silicon content. A comparison was made between surface roughness parameters obtained as a result of the usage of different cooling and lubrication methods such as emulsion cooling, MQL and compressed air cooling. In the experiment, holes with the depth range from 5xD to 15xD were machined using different hole machining strategies.

Effect of the Geometry of Thin-Walled Aluminium Alloy Elements on Their Deformations after Milling.

The aim of this paper is to analyse the effect of the selected geometric properties of thin-walled structures on post-machining deformations. In the study, EN AW-7075 T651 and EN AW-6082 T651 aluminium alloys were used to prepare specially designed thin-walled sample elements, i.e., elements with walls arranged in a semi-open and closed structure and with a dimension of 165 × 262 × 50.8 mm consisting of bottom and vertical stiffening walls and so-called ribs with a thickness of 1 mm. The measurements of the absolute deformations of the thin-walled bottom were performed with the use of a Vista coordinate-measuring machine by Zeiss with a PH10 head by Renishaw. Based on the obtained results, it was found that absolute deformation values were higher for walls arranged in a semi-open structure. It is related to a lower rigidity of the tested structure resulting from the lack of a stiffening wall, which is the so-called "rib". Notwithstanding the geometry of the elements, greater absolute deformation values were recorded following conventional cutting methods. The use of high-speed cutting (HSC) provided positive outcomes in terms of minimising the deformation of thin-walled elements. Additionally, it was found that higher absolute deformations were obtained for EN AW-7075 T651 alloy.

Comprehensive Analysis of a Tricycle Structure with a Steering System for Improvement of Driving Properties While Cornering.

This paper focuses on the development, theoretical and experimental research on the structural units of an unconventional three-wheeled vehicle. The vehicle is designed in order to increase the stability when cornering in a low curvature radius. Current research work describes solutions to increase the cornering stability of either conventional three-wheeled vehicles or, more rarely, unconventional vehicles designed on the basis of complex wheel-tilting mechatronics. Thus, there is a gap in research in respect of consideration of a stability-enhancing mechanism for three-wheeled vehicles based on a combination of tilting and deflection of the front steered wheel in the course of cornering. This paper then compares the stability of a three-wheeled vehicle with one steered wheel in front and two wheels in the rear (1F2R) in conventional and unconventional designs. A particular linear formula for the stability of the three-wheeled vehicle in cornering is derived. This study further deals with the design of the frame intended to hold the unconventional steering mechanism of the front wheel of the vehicle, on the one hand, from the theoretical integrity point of view using CAD-, FEM- and MBS-based software and, on the other hand, from the experimental point of view by determining the multiaxial fatigue life of the test specimens. These were made from the frame structural material and loaded with an equivalent load (bending-torsion) corresponding to the real load of the frame in operation. It was discovered that the designed patented front wheel steering mechanism increased the passing speed by 19% in comparison with a conventional vehicle at the minimum possible radius of a corner. The designed vehicle meets the safety conditions in terms of frame integrity and load-bearing capacity. The vehicle frame is designed with respect to the fatigue life of the material, the results of which are presented in the work. The material employed for manufacturing the frame is aluminum alloy type EN AW6063, which makes the frame lightweight and strong.

New approach for multi-material design: Combination of laser beam and electromagnetic melt pool displacement by induced Lorentz forces

Multimaterial structures are a promising solution to reduce vehicle weight and save fuel or electric energy in automotive design. However, thermal joining of steel and aluminum alloys is a challenge to overcome due to different material properties and the formation of brittle intermetallic phases. In this study, a new joining approach for producing overlap line-shaped joints is presented. The lower joining partner (EN AW 5754) is melted by a laser beam, and this melt is displaced into a line-shaped cavity of the upper joining partner (1.0330) by induced Lorentz forces. The melt solidifies in the cavity to a material and form-fitting joint. This approach needs no auxiliary joining elements or filler materials. Previous investigation to produce spot-shaped joints by using this approach showed that quality and reproducibility were limited by known melt pool dynamics of aluminum alloys (keyhole collapses). For line-shaped joints, the melt displacement can take place behind the keyhole. This allows the displacement process to be spatially uncoupled from the influence of keyhole collapses. The study shows that this improved the process stability and the quality of the joint. The created line-shaped joints were microstructurally characterized by transversal sections. Intermetallic phases were identified by electron backscatter diffraction and EDX analysis. The detected intermetallic phases consist of a 5–6 μm compact phase seam of Al5.6Fe2 and a needle-shaped phase of Al13Fe4. Tensile shear tests were carried out to quantify the load capacity. It was possible to create a joint with a load capacity of about 2 kN.

Cooling rate as a process parameter in advanced roll forming to tailor microstructure, mechanical and corrosion properties of EN AW 7075 tubes

AbstractThe effects of solution heat treatment parameters and quench media as a processing tool for tailoring microstructure, mechanical and corrosion properties in roll forming of EN AW 7075 alloy were studied. The highest yield stress and ultimate tensile strength were obtained for the specimens quenched in water, while the air‐cooled specimens exhibited inferior mechanical properties. Microstructural analysis of specimens showed that except water‐quenched specimens, the parts cooled/quenched in oil, in direct contact with tool steel and air are characterized by coarse precipitates and precipitate‐free zones. The corrosion tests showed that the cooling rate has a pronounced influence on the corrosion resistance and related mechanism of EN AW 7075 alloy. The surfaces of specimens quenched in water remained intact although pitting corrosion took place. The microstructure of the part processed by roll forming was explored in direct comparison. It is revealed that by the employment of quenching nozzles, a high cooling rate similar to the water‐quenched condition can be achieved. Results obtained in the present study pave the way to directly tailor aluminum parts for specific applications.

The effect of surface treatment on the shear properties of aluminium-polypropylene joints manufactured by laser beam

In this article, we evaluated the mechanical response of laser-joined EN AW-6082 aluminium alloy and polypropylene (PP) specimens under quasi-static and cyclic shear loading. In order to increase the strength of the joints, we formed grooves in the aluminium with laser ablation. We determined the effect of PP melt viscosity and heat generated during the joining process on the shear strength of the joints using three types of PP with different melt viscosities. In order to influence the adhesion between the apolar polypropylene and the aluminium, we also treated some PP specimens with maleic anhydride (MA) prior to joint formation. We found that by doing so, the quasi-static shear strength of the joints increased by 50% on average. Furthermore, when we engraved many grooves in the aluminium and treated the PP specimens with MA, the average failure cycle number of specimens could be increased by an order of magnitude.

Mechanical and Microstructural Analysis of Friction Surfaced Aluminum Coatings on Silicon Nitride Ceramic Substrates

The lack of suitable techniques for joining Si_{3}{text{N}}_{4} ceramics with metals has limited the usage of this otherwise outstanding material for composite applications. In this study, aluminum AlMgSi0.5 (EN AW-6060) was coated onto silicon nitride Si_{3}{text{N}}_{4} ceramic substrates using friction surfacing technology. Experimental work revealed that the harmful effects of thermal shock (e.g., substrate cracking, coating delamination) observed with other material combinations can be avoided by selecting materials with a low coefficient of thermal expansion, low Young’s modulus and high thermal conductivity. Design of experiments derived models for coating thickness and bonding strength fit the data well (i.e., the regression model accounts for most of the variation in the response variable). Whereas the coating thickness is predominately dependent on the rotational speed used, the bonding strength is also affected by the traverse speed. Coating thicknesses upto 2.03 mm and bonding strengths of 42.5 MPa were achieved. Deposition rates exceed those of physical vapor deposition by a magnitude of ×1000 and bonding strength is on-par with thin-film metallization. Scanning transmission electron microscope analysis revealed formation of a glassy phase at the interface. Using energy-dispersive X-ray spectroscopy analysis high silicon and oxygen content with smaller percentages of aluminum and nitrogen were detected. High-resolution transmission electron microscope imaging revealed no distinct lattice structure leading to the assumption that the composition is predominantly amorphous and consists of SiAlON.

Analysis of the Effectiveness of Removing Surface Defects by Brushing

The paper presents the results of a study on the effectiveness of removing surface defects by brushing. Damage to machine components usually begins on their surface or in the surface layer area. This determines the development of methods, conditions, and process parameters that will positively affect the stereometric and physical properties of the surface layer. Experiments were conducted in which surface defects were generated on a specially designed test stand. By controlling the load and speed of the defect generator it was possible to affect the geometry, depth, and width of the surface defect. A FEM simulation of the brushing treatment was carried out in order to determine the effect of fibers passing through a surface defect in the form of a groove with a small depth and width. It was shown that for certain conditions of brushing treatment, surface defects could be removed effectively. Moreover, the microhardness of the surface layer after the brushing process was analyzed. Changes in microhardness due to brushing reached up to 50 μm for EN AW-2024 aluminum alloy and up to 150 μm for AZ91HP magnesium alloy. The results demonstrated that brushing was an effective method for strengthening the surface layer and that the value of strengthening in the area of defects depended on the effectiveness of their removal.