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A U t o M o t I v E formed tubes, due to their good formability which can always be regained during complex forming operations by inter-annealing where quenching is needed for age hardening. In chassis parts or wheel applications the benefit is twofold since the weight reduction in the unsprung mass of moving parts additionally enhances driving comfort and reduces noise levels. A well established high Mg containing alloy, AlMg5Mn (AA5182), is used for high strength and complex stampings. For 5xxx alloys containing > 3% Mg the precipitation of ß- Mg5Al8 particles at grain boundaries can result in susceptibility to intergranular corrosion cracking (ICC) by long term exposure at > 80°C. For these conditions special high Mg alloys have been developed with a good compromise for sufficient strength and ICC resistance. For all other cases special high Mg alloys (> 6% Mg) have been introduced which show high strength and strain hardening, thus also enhancing formability. Al-Mg-Mn alloy sheet has also been successfully applied or is currently being tested in many parts for structural support, pedal boxes, heat reflectors, lever arms, etc. Al-Mn EN-AW 3xxx alloys are applied for heat-exchangers which is another success story of aluminium sheet and extrusion applications that started in Europe many years ago. It is an increasing market with intensive R&D, established for advanced lightweight technology for radiators and air conditioning systems in cars (and elsewhere) world wide. New aluminium alloys for automotive applications: Several new product developments were introduced in the SLC project to meet specific demands of the BIW that cannot be met by the present aluminium alloys. For example, a high Mg 5xxx alloy specially dedicated to warm forming [12]. New 6xxx alloys and 7xxx alloys for structural applications were introduced [11], such as ‘crash alloy’ is used for the crash members in the front structure of the SLC model or a ‘roof alloy’ with special attention when placed on steel structure. Here a 6xxx alloy (6013 type) has been introduced [11] with fast paint bake response to withstand the thermally induced plastic deformation. The final SLC structure has a magnesium roof where the finished roof is mounted after the BIW has passed through the paint line. High strength 7xxx alloys applied in aerospace have been tested in the SLC study to determine their potential for weight saving replacing steel in the Golf V Bpillar for a side impact simulation. The alloy selected was a 7081 type alloy with yield strength around 600 MPa in an artificially aged temper. The result of the impact simulation shows that a 3.5mm thick 7081 matches the performance of 2 mm thick boron steel. More importantly the aluminium part is 2.4 kg lighter, so achieving a weight saving of around 40% [11]. Other aspects investigated in detail in the SLC project were: • Heat forming is a new technique for making complex aluminium tubular shapes using internal gas pressure to form hollow bodies or tubes within a warm environment [12]. It provides a competitive alternative to hydro- or superplastic- (SPF) forming. • Tailor welded blanks (TWBs) is a mature product for steel automotive applications easy to apply to aluminium. There is only one example of aluminium TWBs in series production; the backplate of the front wheel house of the Lamborghini Gallardo [11]. The SLC project proved that aluminium TWBs can be applied for demanding deep drawn parts at higher volumes. Fig. 3 shows the geometry of the TWB and a final result of a pressed part of door inner. The aluminium TWBs have been successfully stamped to produce inner door panels, using a two-step operation to obtain 140 mm deep drawing depth without breaks in laser weld seam. Geometrical accuracy of stamped panel was checked and found to be acceptable for production use, showing that the process is technical feasible. Laser brazing steel-aluminium: The next logical step after steel TWBs and aluminium TWBs is a combination steel-aluminium TWB. This, however, is more complicated because of the joining of steel to aluminium. Conventional fusion welding is gives poor quality joints due to the formation of brittle Fe-Al intermetallics. Besides the well-known technologies such as mechanical fastening and adhesive bonding, a recently developed technology called laser brazing shows good potential for joining steel to aluminium [11]. Aluminium in the final SLC body concept The final SLC-body concept (Fig. 4) chosen shows an optimum between weight reduction of 95 kg (34%), i. e. a weight saving of 41% vs. reference (from 65 to 110 kg) and a additional part costs of 7.8 €/kg. It has an Mg roof and a steel floor frame (i. e. lighter on top than underneath) and torsion ring of the side structure in form-hardened high strength steel combined with an aluminium sheets frame. For the inner B-pillar TWB steel sheets are used with an external aluminium skin. Aluminium is used as sheet panels and as extrusion in front rail and for bumper and crash elements and in the rear underbody rail and wheelhouse structure as HPDC (high pressure die cast). Compared to the good formable (conventional) steel grades aluminium is less formable, so the manufacturabil- Fig. 3: Door inner produced from TWB ity of such parts is not obvious. ➝ 30 ALUMINIUM · 9/2009
© Kastenhuber Wergeagentur/Fotodesign · Tel. (0 9142) 204 558 S P E C I A L A L U M I N I U M I M A U t o M o b I L Fig. 4: Final SLC-body multi material concept The procedure is to start with a simulation and by mutual agreement with design and engineering departments, to adapt the design of a part so it can be produced (simulated) while it fulfils all requirements. This interactive development procedure can take some time, but in case of the SLC demonstrator it is sufficient to show the PROFHAL ALUMINIUM PROFIL BEARBEITUNG GMBH Ein Unternehmen der HAARMANN-GRUPPE Dettenheimer Straße 30 D-91781 Weißenburg Tel. +49-(0)91 41-8 55 65-0 www.profhal.de feasibility, not necessarily to develop a failure free simulation. Aluminium sheet forming simulation As an example the side panel is shown based on present steel design. It is a very difficult part for aluminium be- A U t o M o t I v E cause of steep deep drawing around sharp corners. Easiest – but unrealistic – solutions for SLC are to split the panel into more sections or to drastically change the design by creating corners with larger radii. Here the simulation strategy is to investigate different options to control material flow to lower the strain in critical areas, using AutoForm incremental software 4.1. Input material data are taken from the SLC SP2 database generated, tool geometry is generated by the program based in the CAD files of the parts. Fig. 5 shows the initial simulation. It is obvious that a straightforward pressing of the part will not lead to an OK part. Indicated at the problem areas are the options to improve the material flow. To improve the formability of the side panel draw beads are included in the centre sections and the radius is adjusted to 10 mm in the doors. Increasing the radius and the draw beads are clearly an improve- ➝ PROFHAL entwickelt, fertigt und veredelt hochwertige Aluminium-Profil-System- Komponenten für unterschiedlichste Anwendungsgebiete. INDIVIDUELLE LÖSUNGEN AUS ALUMINIUM 31 ALUMINIUM · 9/2009 ALUMINIUM · 9/2009 31 www.haarmann-gruppe.de
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