Ahmed Rahem

Mechanical properties of aluminium–copper B206 alloys with iron and silicon additions

Abstract Mechanical properties of B206 aluminium alloys with additions of iron and silicon were studied to investigate the combined effect of these additions on tensile strengths and ductility. Properties are highly influenced by the iron to silicon ratio and the nominal concentration of the single elements. The best properties were obtained with both a ratio close to one and low concentrations of iron and silicon. Present experimental results show that it is possible to multiply by two or three the present limit of 0·1 wt-%Fe in these alloys at natural aging (T4) and still obtain the minimum of 7% elongation required by the automotive industry. At artificial aging (T7), it will be very difficult however to reach the 7% elongation with ∼0·2 wt-%Fe and 0·2 wt-%Si, while this seems impossible with ∼0·3 wt-%Fe and 0·3 wt-%Si. It was found that macrosegregation of Cu in the gage section of the ASTM B108 test bars is responsible for an enrichment of 0·8–0·9 wt-% of this element in the test zone. This has produced microstructures saturated in Cu with little Al2Cu phase remaining after the solution heat treatment. Owing to the low amount of this phase and the round shape of the particles, the remaining Al2Cu phase did not have a significant impact on the ductility. One benefit of working with a Cu saturated microstructure is that one can estimate the true temperature of the solution heat treatment by conducting a post-analysis of Cu content in the dendrites. This should be helpful to reduce the variability in properties and to improve the temperature distribution in heat treating furnaces.

Numerical Studies on the Production of Variable Thickness Aluminium Tubes for Transportation Purposes

Nowadays application of light alloys like aluminium in automobile industry has found a striking role. Higher strength over weight ratio which causes lower fuel consumption seems to be the first reason. Also some other reasons like ease of manufacturing, protection against corrosion and ease of recycling are other motivations for car designers to use various aluminium alloys as much as possible. Due to lack of variable thickness tubes, they have not found a lot of applications in the car component design. This paper aims to introduce these types of tubes to automotive industry. Also these tubes are one of the essential elements in the complementary processes like tube hydroforming and cause ease of production and decreasing risk of scrap in manufacturing cycles. Tube drawing is one of the mostly used methods for reducing thickness and/or diameter of tubes which, can be classified in four categories like sinking (without mandrel), float mandrel, fixed mandrel and ultrasonically moving mandrel. This paper presents numerical studies that have been done on the drawing tubes with variable thickness. The influence of process variables on material thinning and formability in 63.5mm outer diameter, 2.62 mm wall thickness AA6063 aluminium alloy tube, were investigated and optimised. Validation of the numerical simulation on the different parameters setting will be performed by comparing the final shape and deformation, measured from the tested part. Acceptable agreement between numerical and experimental results was observed.

Experimental Exploration of the Aluminum Tube Drawing Process for Producing Variable Wall Thickness Components used in Light Structural Applications

Tube drawing is a well known process involving at room temperature the reduction of diameter and wall thickness to obtain specified values. The initial tube is drawn into a die of a smaller opening and its thickness achieved by use of a mandrel. Usually, the mandrel has a land area which diameter defines by sizing the inside diameter of the final tube. Some structural components found in cars, aircrafts and other vehicles require bent or hydroformed tubes of lower weight. It is of interest to have tubes of varying axial or circumferential thickness so that to reduce overweight in low stressed areas and reinforce it otherwise. However, the production of tubes of varying thickness is more difficult in reason notably of higher metal flow stresses in the deformation zone and the need to control precisely the mandrel position during drawing. Axial thickness variation is obtained using a mandrel with stepped lands or with a slight taper while circumferential variation is achieved with a mandrel of desired internal or external shape (e.g. oval). In this paper, two techniques for axial tube wall thickness variation and one technique for circumferential variations are introduced and tested. First, the techniques to produce drawn tubes with thickness variations are presented. For testing, a small (335 kN) instrumented tube drawing machine is used. Details on this machine, process lubrication, monitored data and on the tooling implemented are also presented. Initial tubes are mainly AA6063 extrusions of 63.5mm O.D. and 2.6mm thick and the final outside diameter, i.e. the inside diameter of the die, is about 47.5 mm. AA6061 tubes are also drawn. Starting with drawing tests without mandrel, the natural flow of the tube and the drawing force involved are measured. Secondly, tubes of 4 different thicknesses are produced with a stepped mandrel and the strain hardening effect on mechanical properties established. Using a tapered mandrel, tubes of continuously varying wall thickness are tested. Higher local pressure in the die corner radius restricts proper lubrication in certain conditions but results are promising in most cases. We also study the effect of thickness rate of change along the tube. Finally, tests with a stepped oval mandrel provided good results for circumferential thickness variations. The dimensional quality is measured using a coordinate measuring machine and mechanical properties obtained from tensile tests in both initial and drawn tubes. Finally, despite some minor problems, the techniques proposed can efficiently produce tubes with thickness variations and have a very strong potential for industrial use.

Crashworthiness of Aluminium Tubes; Part 1: Hydroforming at Different Corner‐Fill Radii and End Feeding Levels

The automotive industry, with an increasing demand to reduce vehicle weight through the adoption of lightweight materials, requires a search of efficient methods that suit these materials. One attractive concept is to use hydroforming of aluminium tubes. By using FE simulations, the process can be optimized to reduce the risk for failure while maintaining energy absorption and component integrity under crash conditions. It is important to capture the level of residual ductility after forming to allow proper design for crashworthiness. This paper presents numerical and experimental studies that have been carried out for high pressure hydroforming operations to study the influence of the tube corner radius, end feeding, material thinning, and work hardening in 76.2 mm diameter, 3 mm wall thickness AA5754 aluminium alloy tube. End feeding was used to increase the formability of the tubes. The influence of the end feed displacement versus tube forming pressure schedule was studied to optimize the forming process operation to reduce thinning. Validation of the numerical simulations was performed by comparison of the predicted strain distributions and thinning, with measured quantities. The effect of element formulation (thin shell versus solid elements) was also considered in the models.

Effect of Cross Section Reduction on the Mechanical Properties of Aluminium Tubes Drawn With Variable Wall Thickness

Variable thickness tube drawing is a new process for the production of high performance tubes. In this study, experiments were conducted to evaluate the effect of cross section reduction on the microstructure and mechanical properties of variable thickness aluminium tubes drawn using two different position controlled mandrel techniques. Various tubes with three different outer diameters were subjected to cold drawing at room temperature from 11 to 41 cross section reduction. The local mechanical properties were determined from tensile tests carried out on specimens cut from different positions in the tubes parallel to their axes. The distributions of the Vickers hardness over the surfaces at 0 deg and 90 deg to the drawing direction were examined. It was found that the microhardness, yield strength, and ultimate tensile of the deformed samples increase and the corresponding elongation decreases with the increase of cross section reduction. Also, the anisotropy in microstructure and mechanical properties is more significant with increasing of cross section reduction. The evolution of mechanical properties of drawn tubes versus cross section reduction depends on the mandrel shapes and initial tube outer diameter. This study helps to further understand the microstructure and mechanical properties evolutions during tube drawing process with variable thickness.

Perspectives for the Application of Variable Thickness Aluminium Tubes in Hydroforming of Complex Tubes

Tubular products have very important applications in various areas especially in the transportation industries. For instance, in the structure of cars there are various tubular products like roof headers, engine cradles, roof rails and frame rails with complex geometries which most of them need multiple steps like tube drawing, tube bending and hydroforming for their production. Based on the recent studies by this group, it was proven that in most of the structural tubular parts in the cars it was not necessary to have constant thickness along the axial direction of tube and it will be considered as overdesign and the overall weight of structures can be reduced considerably by using variable thickness tubes. In this paper, the variable thickness tube drawing and its applications in the tube bending and hydroforming applications were studied. The results showed that this process can have important role in reduction of defective parts in the production of complex tubes by the tube hydroforming method. However especial considerations should be taken into account in the design of thickness distribution along axial direction of these kinds of tubes to avoid problems in the drawing step and as well in the bending and hydroforming steps.

Optimization on the Production of Variable Thickness Aluminium Tubes

The variable thickness tube drawing is a new modification in the tube drawing methods which enables production of axially variable thickness tubes faster and easier in comparison with other similar methods like radial forging or indentation forging. The production of this type of tubes can be used in optimum design of mechanical parts which do not necessarily need constant thickness along the axis of tube and this method can strikingly reduce the overall weight of parts and mechanical assemblies like cars. In this paper, the variable thickness tube drawing were parameterized in a MATLAB code and optimized with the Ls-Opt software as an optimization engine and Ls-Dyna as a FE solver. The final objective of this optimization study is to determine the minimum thickness which can be produced in one step by this method with various tube dimensions (tube thickness and outer diameter). For verification of results, some experiments were performed in the tube drawing machine which was fabricated by this research group and acceptable correspondence was observed between numerical and experimental results.

Crashworthiness of Aluminium Tubes; Part 2: Improvement of Hydroforming Operation to Increase Absorption Energy

The motivation to reduce overall vehicle weight within the automotive sector drives the substitution of lightweight materials such as aluminium alloys for structural components. Such a substitution requires a significant amount of development to manufacture structurally parts such that the energy absorption characteristics are not sacrificed in the event of crash. The effects of the manufacturing processes on the crash performance of automotive structural components must be better understood to ensure improved crashworthiness. This paper presents results of an experimental and numerical investigation of the crash response and energy absorption properties of impacted hydroformed aluminium alloy tubes. Crash experiments on hydroformed tubes were performed using a deceleration sled test at the General Motors Technical Center. Results from axial crush testing showed that an important parameter that influences the energy absorption characteristics during crash was the thickness reduction caused by circumferential expansion of the tube during hydroforming. It was found that that the energy absorption decreased as the corner radius decreased, which results because of increased thinning. Sensitivity studies of end feeding parameters, such as end feed level and profile, were carried out to evaluate their impact on the energy absorption of the aluminium tubes.