Papers by Keyword: Roll Bonding

Abstract: With the increasing demand for lightweight materials, the combination of aluminum and magnesium sheets enables the development of advanced laminates with a balanced combination of strength and ductility, making them suitable for forming applications. This work investigates the effect of rolling temperature on the mechanical behavior and formability of AA1050/AZ31/AA1050 sheets produced by roll bonding in the temperature range of 250–450°C. Tensile tests showed that the yield stress is weakly affected by rolling temperature, whereas the ultimate tensile strength increases up to 350°C and then stabilizes. The elongation at fracture increases monotonically with temperature, indicating improved ductility at higher rolling temperatures. Microhardness measurements revealed softening of the aluminum sheets with increasing temperature, while limited variations were observed in the AZ31 sheet. Formability was evaluated by Erichsen Cupping test. The maximum load and extension at break remained nearly constant over the investigated temperature range; however, higher rolling temperatures led to reduced delamination and improved interfacial bonding integrity during deformation. The results indicate that roll bonding at elevated temperatures promotes better strain distribution and enhanced bonding quality. Overall, roll bonding at 450°C provides the most favorable combination of mechanical performance, formability, and interfacial stability, making the produced sheets suitable for lightweight forming applications.

Abstract: To increase the safety of steels in high performance cases like crash energy absorption, even better properties of the materials are necessary. To advance this research, a TWIP and a TRIP steel were combined in a laminated composite via roll bonding at 450 °C with the goal of using accumulative roll bonding (ARB) in later research to further enhance the properties reaching an ultra-fine-grained material. Two different TWIP layer thicknesses (2 mm and 3 mm) were experimentally roll bonded with a 3 mm thick TRIP layer each using a 4-high rolling mill. A modular Python-based simulation incorporating coupled solving of ordinary differential equations of the temperatures and the horizontal stress changes of the layers were implemented to predict deformation and bonding behavior. Simulated results matched well with experimental data in terms of final geometry and temperature, while roll force deviations indicated the need for the refining of the used model. Furthermore, experimentally asymmetric layer relationships at the beginning and the addition of a thin (10 µm) Ni interlayer were found to enhance bond strength in high-strength steel laminates.

Abstract: Cladding of steel is mainly carried out by hot rolling. This process is very labor-intensive and, therefore, expensive. Cold plating has been used successfully to produce bimetals and could also be an alternative manufacturing process for cladded carbon steel composites. So far, however, only thin narrow IF-steels sheets were successfully cold plated. Different pretreatments and process windows have been used to successfully produce a cold roll-cladded composite of various steel grades on a cold rolling test facility. While joining two similar steels was relatively easy, the combination of different steel alloy compositions was more difficult. Higher necessary forces and edge cracks complicated the experiments. A slight warming of the sheets before joining had a positive effect on the production of the composite. From today's perspective, the required high rolling forces do not allow scaling up to large-scale production.

Abstract: Roll bonding is a joining-by-forming process to permanently join two or more layers of different materials by hot or cold rolling. One of the typical industrial applications is aluminium sheets for heat exchangers in automobiles. During roll bonding the layers are fed into the rolling stand with parallel surfaces. Due to the plastic deformation in the roll gap metallic bonds between the layers are achieved. Several theoretical models have been published to describe the process, e.g. Zhang & Bay. These models have mostly been developed for cold rolling and describe the bond strength based on surface enlargement, contact pressure and flow stress. Since these models are developed for cold rolling, they are not temperature depending. Heat exchange is usually neglected and de-bonding after the roll gap is not accounted for. However, for hot roll bonding the above mentioned assumptions do not hold true. To understand the mechanisms of hot roll bonding industrial and laboratory scale investigations have previously been conducted. Based on the findings a FE framework for hot roll bonding was developed. This FE framework accounts for the possibility of de-bonding after the roll gap but is restricted to isothermal conditions. However, for a roll bonding simulation it is essential to take the temperature influence into consideration. Therefore, this paper presents an extended version of the FE framework which accounts for temperature dependent material flow, compatible definition of thermal & mechanical interactions and bonding status related heat exchange. To verify the new features of the extended FE framework a roll bonding test case is employed. Mechanical and thermal interactions as well as the current flow stress are calculated in subroutines in order to enable a fully coupled thermal stress simulation. The results show that with this extended FE framework the influence of non-isothermal conditions on material flow and bonding status as well as the feedback effects of bonding status to heat exchange have been successfully integrated in hot roll bonding simulations. This fully coupled thermal stress simulation is the first step towards multi-pass roll bonding simulations.

Abstract: Roll bonding is a process to join two or more different materials permanently in a rolling process. A typical industrial application is the manufacturing of aluminum sheets for heat exchangers in cars where the solder is joined onto a base layer by roll bonding. From a modelling point of view the challenge is to describe the bond formation and failure of the different material layers within a FE-process model. Most methods established today either tie the different layers together or treat them as completely separate. The problem for both assumptions is that they are not applicable to describe the influence of tangential stresses that can cause layer shifting and occur in addition to the normal stresses within the roll gap. To overcome these restrictions in this paper a 2D FE-model is presented that integrates an adapted contact formulation being able to join two bodies that are completely separated at the start of the simulation. The contact formulation is contained in a user subroutine that models bond formation by adhesion in dependence of material flow and load. Additionally if the deformation conditions are detrimental already established bonds can fail. This FE-model is then used to investigate the process boundaries of the first passes of a typical rolling schedule in terms of achievable height reductions. The results show that passes with unfavorable height reduction introduce tensile and shear stresses that can lead to incomplete bonding or can even destroy the bond entirely. It is expected that, with adequate calibration, the developed FE-model can be used to identify conditions that are profitable for bond formation in roll bonding prior to production and hence can lead to shorter rolling schedules with higher robustness.

Abstract: In the last decade, wide research was carried out on developing light-weight materials with improved mechanical properties, for instance comparable specific stiffness and strength, improved isolation, superior vibration and sound damping properties. To satisfy the increasing demands, Metal-Polymer-Metal Laminates have been numerously developed. Here, a short background of composites structures is presented.

Abstract: In this study the bonding properties of three layer-plated aluminum sheets are investigated. The alloys applied in specific layers were as follows: AlMn1Si0.8 (core alloy) and AlSi10 (liner). The bonding was performed on a Von Roll experimental roll mill using hot rolling. The experimental temperatures were 460, 480 and 500 °C, respectively. To qualify bond development, T-peel test was used. The test was performed using an Instron universal material testing machine. T-peel test can be well used for the qualification of bond strength as the peel-off force and bond value developed on contacting surfaces are proportional. In addition to T-peel test, optical micrographs and SEM micrographs were also captured, in which typical bond faults were sought. The study aims at modelling the technology used in industry and exploring some typical bond faults as well as suggesting the causes generating these and their remedy. The impact of surface roughening before heating was studied as well. Also, the study aimed at confirming the suitability of T-peel test to qualify bond strength.

Abstract: Innovative product characteristics can be realized by hot roll bonding of two or more layers of different materials. To optimize the roll bonding process, an approach to align the strength differences in both materials by a temperature difference between the layers has been proposed. Therefore, the temperature distribution has to be investigated by finite element (FE) simulations. In these simulations the heat transfer coefficient (HTC) between the two aluminum layers is of great importance. With this coefficient the temperature transfer between the two layers can be determined in order to estimate the temperature field and the material strength difference in the layers.In hot roll bonding there are two ranges for the HTC depending on whether bond formation takes place or not. This effect can be used to determine at which pressures bond formation starts. To evaluate the HTC for this application and to determine its value ranges, a simple setup has been developed. This setup allows conducting experiments under defined temperature and pressure conditions. The resulting force-time measurements were used as input values for inverse FE-simulations, with the goal to gather the HTC by inverse modelling the temperature distributions of the specimens. First results show that the range of the pressure dependent HTCs leads up to 21 kW/(m²K) in the unbonded range. In the range where bonding occurred between the specimens, values over 150 kW/(m²K) were estimated. The data for the HTC was implemented in roll bonding simulations as an interaction property. A comparison between the simulated temperature curve and a measured temperature curve during roll bonding showed a good agreement between the temperature values.

Abstract: Composite sheet of Twin Roll Cast (TRC) AZ31-Mg alloy and industrial pure Al-1050 was fabricated as Al/Mg/Al with a hot roll bonding process. As the diffusion zone at the interface between the layers plays a crucial role in the formation of bonding strength and formability of clad sheets. It is important to describe the processes of inter-diffusion layer generation in order to assess the abilities of the laminate composites for further processing. Thus, the aim of this study was to investigate the development of the bonding strength, microstructure and mechanical properties of the bonding interface directly after roll bonding and additionally post-annealing processes. Microstructure characterization techniques such as optical and scanning electron microscopy including energy dispersive X-ray analysis (EDX) were applied to investigate the bonding area. No inter-metallic phases were present directly after the roll bonding process. The creation and growth of Al₂Mg₃ and Al₁₂Mg₁₇ phases were apparent after annealing at temperatures of 250 to 400 °C at different times ranging from five to 120 minutes. The results prove that the growth rate of inter-metallic phases increases considerably with an increase in the annealing temperature. The micro-hardness of the interface-area was also investigated. It was observed that the two inter-metallic phases were significantly harder than the substrate Mg and Al. In order to examine the influence of the inter-metallic phases on the resulting bonding strength after the annealing process, the shear bonding strength test has been conducted for different samples that were annealed at different heat treatment conditions. The results indicate that the optimum annealing temperature is 200 °C leading to a maximum bonding strength. Moreover, the mechanical properties of the composite after roll bonding and post annealing were determined by means of room temperature tensile test. The fracture mechanism after tensile test was also discussed.Keywords: Roll bonding, Al/Mg hot roll bonding, Twin roll cast AZ31, bonding strength

Abstract: Roll bonding is a joining-by-forming process, in which two or more metals are permanently joined through pressure and plastic deformation, which causes the creation of a metallic bond. The bond formation is a complex process based on various process conditions in the joining zone, such as strain, normal pressure, temperature, strain rate, shear strain and surface condition. Since an individual variation and analysis of the influencing parameters is usually not possible during the rolling process, a specific experimental setup for the investigation of the joining mechanisms is necessary. In this paper, a testing procedure has been developed to determine the bond strength in joining-by-forming processes. The material combination chosen was AA2024/AA1050 as used in aircraft applications. AA2024 sheets are cladded with pure aluminum to improve the corrosion resistance. The performed experimental parameter study confirms the expected influencing factors and is used to determine parameters of a bonding model, which can be integrated in a finite element simulation.