Papers by Keyword: Aluminum

Abstract: A cold roll-bonding (CRB) process is applied to fabricate a multi-layer Al sheet using AA5052 and AA6061 alloys. The rolling is performed for four-layer sheets in which AA5052 and AA6061 sheets are stacked alternately after surface treatments such as degreasing and wire brushing. The 4-layer sheets with a thickness of 8 mm were roll-bonded to 2 mm by rolling at total reduction of 75%. The as roll-bonded Al sheets are then processed by natural aging (T4) and artificial aging (T6) treatments. T4 and T6 treated specimens showed a typical recrystallization structure over all regions of AA5052 and AA6061. The average grain diameter of T4 and T6 specimens was about 15 μm, which is almost the same. In addition, the Al sheet showed a heterogeneous hardness distribution in thickness direction. After the aging treatments of T4 and T6, the strength rather decreased and the elongation increased. It is found that new multilayer Al sheets made of AA6061 and AA5052 alloys, exhibiting various mechanical properties can be fabricated through the CRB and subsequent aging treatments.

Abstract: High-strength and recycling tolerable aluminum alloys make a significant contribution to weight reduction in modern lightweight construction. The advantages of aluminum alloys in terms of their low density combined with high strength can be significantly improved by the alloy composition. In contrast to the conventionally established process route, high-magnesium alloys can be produced using the twin-roll strip casting process. This allows additional process steps such as hot rolling and annealing to be drastically reduced in the economical production of near-net-shape strips, saving emissions and energy consumption. The strip casting process has already been applied to numerous aluminum alloys and enables their production, although the understanding of advanced alloys in this area is not yet fully understood because of its limited production in industry-related research due to the complexity of the process. However, transferring the high strength generated during rapid solidification into usable sheet performance remains challenging, especially at elevated Mg contents, where segregation, casting-related defects, and solute-affected recrystallization can limit ductility and processability. This study investigates the potential of a high-magnesium aluminum alloy produced by vertical strip casting. The properties of the alloy are correlated with the microstructural and mechanical characteristics and developed on the basis of an industrial reference alloy. For this purpose, an EN AW 5182 and an AlMg10 alloy were processed. The results show that high-magnesium alloys can be produced and processed using strip casting. In terms of the high-magnesium alloy, improved results can be achieved compared to the industrial EN AW 5182 alloy. Key findings: The strength of high-magnesium alloy is significantly above those of the EN-AW 5182 after strip casting enabling nearly 600 N/mm² tensile strength, but the final properties are below this potentially possible characteristic after strip casting, presumably due to non-ideal recrystallization and an insufficiently adapted process route including rolling and annealing parameters.

Abstract: The utilisation of friction-induced solid-state recycling, methodically adapted to the CoNform process, facilitates the continuous production of semi-finished products. The material intended for recycling is conveyed continuously via a rotating wheel. The volume flow is influenced by fixed surfaces, deflections, and constrictions, thereby creating an asymmetrical flow profile. In order to effect a change in the mechanical properties of the semi-finished product, the material fed into the process can be modified. This enables the amalgamation of two alloys or the direct transition between them. The inhomogeneous flow conditions present within the tool give rise to the mixing of materials, thereby creating a graded multi-material zone. The multi-material zone was divided into different areas and traced back to the process conditions. Within the transitions, the connections between the alloys were examined, as well as the influence on the boundary layer. Material properties were determined for the individual areas and located along the length of the profile.

Abstract: The most common structural material used in the construction sector is steel-reinforced concrete. However, concrete cracking and reinforcement corrosion demand constant monitoring as well as timely and costly maintenance activities. Furthermore, concrete has substantial environmental impacts, being responsible for about 7% of total CO₂ emissions worldwide. Innovative materials in construction engineering have been studied with the goal of improving the sector’s environmental performance, mostly by reducing cement content in concrete. In this context, assessing the environmental profile of such innovations is essential to avoid shifting environmental burdens elsewhere. This study evaluates the climate change impact of a novel reinforced concrete that incorporates calcined blue clay as a supplementary cementitious material and Aluminium (Al) as reinforcement. Using a cradle-to-gate Life Cycle Assessment (LCA), the climate change impact of this innovative material is compared with that of conventional steel-reinforced concrete. The result show that the climate change impact of the innovative concrete is 46% less than that of the incumbent solution. Acknowledging the early development stage of the new concrete and the limitation regarding data robustness, this work contributes to the problem-solution space and provides direction to further explore possibilities for fully unlocking the new material’s potential, so it can outperform the incumbent one in terms of greenhouse gas emissions in the future.

Abstract: Application fields and requirements for roll-cladded cooling plates are continuously rising. Especially as part of the thermal management systems in battery electric vehicles (BEV), the share of roll-cladded cooling plates is growing. A deeper understanding of the deformation regime in the roll bite is needed to completely fulfill the high quality, performance and cost requirements of the automotive industry Whereas most cause-effect relationships in the roll-cladding process have been scientifically evaluated, the influence of separating agents on the deformation regime in partial roll-cladding has not yet been investigated. To examine this relationship, an experimental set up is created and trials are conducted on a laboratory size roll-cladding mill. Two different aluminum alloy blanks are joined together under temperature by roll-cladding without the application of strip tensions and with different separating agent patterns. The results show: Firstly, there is a correlation between the materials’ relative flow stress difference and their relative deformation. Secondly, the separating agents’ areal share over the blank width significantly impacts the deformation regime in the roll bite. Thirdly, in areas with separating agent there is a correlation between the surface elongation of the bottom blank and the elongation of the contact interface between the blanks, which governs the later cooling channel tolerances. To use the results in the industrial application, the impact of so far neglected parameters such as strip tensions have to be considered in future research.

Abstract: Optimizing the performance and reliability of welding techniques for dissimilar aluminum (Al) to titanium (Ti) is a promising way to establish new applications in aerospace industry. Due to structural weight reduction, lightweight materials can help to minimize fuel consumption and save emissions. Solid-state welding technologies allow short joining cycles and metallurgical changes, residual stresses and severe intermetallic compound formation can be reduced by limited thermal exposure. Besides temperature and plastic deformation, intimate contact plays an important role for diffusion. In this work, AlMgSi alloys with systematic variations of Mg and Si alloying elements, were welded to Ti6Al4V (Ti64) by refill Friction Stir Spot Welding. The focus lays on the effect of Ti64 sheet surface roughness, varied by different surface preparations. Additionally, the influence of the plunge depth, the distance between the tool and the Ti64 sheet surface is analyzed. It was found that a reduced tool to interface spacing has a beneficial influence on joint integrity. Grinding trenches allowed better bonding compared to the pit-like surface structure generated by sandblasting, which led to an increase in mechanical lap-shear properties. Knurling the grinded surfaces resulted in high standard deviation, as most likely not the whole interface area was bonded. However, the partially outstanding properties showed that a beneficial effect can be expected due to mechanical interlocking mechanisms, when sufficient diffusion is ensured.

Abstract: Nowadays, the growing demand for sustainable solutions in manufacturing has shifted research attention toward innovative recycling strategies. Among these, the Solid-State Recycling (SSR) technique has emerged as a viable approach to transform metal swarf into new products. Within the SSR family, friction stir extrusion (FSE) has gained particular interest as a promising method for producing wires from metal scraps, but recently, it was also employed for tube manufacturing. In literature, tube production via chip recycling often involves multi-step approaches, first consolidating/homogenizing the recycled chips and then extruding. In other cases, the tubes are manufactured directly from a bulk material, losing the sustainable goal. For this reason, this study aims to propose a single-step process in which aluminium chips are directly turned into a consolidated tube without any intermediate step. In addition, specific attention was given to the study of tool geometry, aiming to investigate the effect of a tapered tool’s shape on the material flow and the overall process performance. Experimental tests were conducted to characterize the microstructure of extruded tubes and to calibrate numerical simulations employed for investigating process dynamics. Results revealed that the reduced contact diameter of the chamfered tool generated lower processing temperatures but higher strain levels, fundamentally shifting the bonding mechanism from thermal assistance to mechanical dominance in oxide film breakage. Microstructural analysis demonstrated that the flat tool, characterized by predominant frictional heating and lower deformation, produced larger grain diameters due to thermally induced coarsening. Conversely, the chamfered tool yielded significantly refined grain structures through severe plastic deformation and dynamic recrystallization under suppressed thermal conditions, indicating superior consolidation quality and enhanced particle bonding.

Abstract: Skin-pass rolling is commonly used to adjust the surface quality of high-strength aluminum alloys. Lubrication plays an important role in this process, as it minimizes material adhesion to the work roll, extends its service life, and also influences the contact conditions and the final surface topography. However, most numerical studies represent lubrication only through an effective friction coefficient. In this work, a finite-element framework that explicitly accounts for lubricant entrapment in engineered surface pockets by using a coupled Eulerian-Lagrangian (CEL) approach is introduced to investigate lubricant-topography interaction. The skin-pass rolling process is approximated by a plane-strain upsetting test to represent the parameters relevant for mapping the interaction between lubricant and mechanical stress, as the rolling process has a large number of influencing factors. The precipitation-hardenable aluminum alloy EN AW-6016 is modeled with rate-dependent plasticity based on experimental flow curves, while the lubricant is represented as a Eulerian material governed by an equation-of-state formulation. The effects of strain rate, friction and different lubricant filling levels in surface pockets are analyzed. The results show that variations in friction mainly affect the global force level, while the presence of lubricant leads to changes in local deformation and stress distributions. Fully filled pockets require higher forming forces due to lubricant compression, whereas partially filled pockets show behavior close to dry conditions. The CEL approach proves suitable for modeling lubricated plane-strain upsetting tests and provides a basis for further investigations of lubricated skin-pass rolling processes.

Abstract: Transverse (charge) welds form during billet transitions in aluminium extrusion when incoming material progressively replaces residual metal inside the die, defining the length of extrudate that must be scrapped. This study aimed to quantify charge weld evolution under industrially relevant conditions that are often underestimated in scrap length assessment, including multi-cavity flow imbalance, non-symmetric multi-profile placement, and billet-to-billet thermal stabilisation effects. Three case studies were analysed using finite element simulation in QForm UK: (i) the International Extrusion Benchmark 2023 multicavity die producing three hollow tubes with intentionally varied port and bearing designs, (ii) an industrial two-profile die with translated (non-mirrored) profile positioning to avoid post-extrusion rotation, and (iii) a complex industrial profile extruded over multiple consecutive billets. The benchmark study demonstrated strong agreement between simulation and experimental charge weld evolution for two profiles, supporting the reliability of the predicted cavity-dependent differences driven by port volume. In the translated two-profile configuration, the charge weld cut length required for full purity increased from 1674 mm to 1940 mm (+16.0%), and by +15.9% under the 95% industrial criterion (1458.1 mm vs 1690.7 mm). Billet-to-billet variability was substantial, with charge weld length increasing by +70.1% from the first to the fifth billet (2819.0 mm to 4791.7 mm), before stabilising. Overall, the results show that charge weld length is governed by residence-time differences through ports and flow channels, requiring profile-specific assessment and consideration of process stabilisation. In this context, FE simulation provides an effective means to localise the mixed zone and to support die optimisation strategies aimed at reducing scrap.

Abstract: Of interest for military applications is the repair of damaged fastener holes on aircraft. One of the preferred repair processes, specifically for aluminum alloy 7075 (AA 7075), is friction stir additive manufacturing (FSAM) to avoid hot cracking and high residual stresses. Some of the largest challenges with this additive manufacturing process, however, are the high axial force requirement to deposit the consumable tool onto the substrate material as well as the amount of downtime necessary for repair. One possible solution is the utilization of electrical assistance during the FSAM process, since the yield strength of the alloy decreases with increasing current density when depositing bar stock. This work investigates utilizing electrically assisted friction stir technology on a conventional knee mill, which is commonly used in depots and machine shops, to showcase that repairs can be completed on commercial, commonly available equipment with decreased repair time. Varying current addresses an efficiency challenge of additive manufacturing by lowering the dwell time necessary for deposition. While higher current densities would address one of the largest concerns of FSAM – the high force requirements, the ability to repair holes using a retrofit conventional system would allow for more point-of-need applications. With the eventual application of military interest in mind, 7.95 mm (5/16”) diameter holes are drilled and repaired using FSAM via a conventional Bridgeport knee mill for use in typical machine shop locations. The material properties of AA 7075 stock material are compared to FSAM hole repairs completed with and without electricity incorporated.