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1 Sheet metal forming of magnesium wrought magnesium wrought alloys formabilityand process technology Abstract New developments at the for Metal Forming and Metal Forming Machine Tools show that magnesium sheets possess excellent forming behavior if the process is conducted at elevated temperatures For the evaluation of mechanical properties relevant for forming of magnesium sheets uni axial tensile tests have been carried out at various temperatures and strain rates Deep drawing tests with magnesium alloys AZ31B AZ61B and M1 show very good formability in a temperature range between 200 and 2508C Besides temperature the influence of forming speed on limit drawing ratio has been investigated The obtained results lead to the conclusion that it is possible to substitute conventional aluminum and steel sheets by using magnesium sheet metal wrought alloys 1 Introduction In order to reduce fuel consumption general efforts have been made to decrease the weight of automobile constructions by an increased use of lightweight materials In this framework magnesium alloys are of special interest because of their low density of 1 74 g cm3 Presently magnesium alloys for the use as automobile parts are mainly processed by die casting The die casting technology allows the manufacturing of parts with complex geometry However the mechanical properties of these parts often do not meet the requirements concerning the mechanical properties e g endurance strength and ductility A promising alternative has to be seen in components that are manufactured by forming processes The parts manufactured by this technology are characterized by advantageous mechanical properties and fine grained microstructure without pores 1 However a widespread use of forming technologies for the processing of magnesium alloys is restricted because of insufficient knowledge about the forming technologies and suitable process parameters that have to be applied 2 3 Automotive body constructions offer a great potential for the application of magnesium sheet metal components In general the automotive body completely consists of sheet metal parts and represents a share of about 25 of the entire vehicle mass Therefore the substitution of conventional sheet materials by magnesium sheets would lead to essential weight savings in this application 2 2 Plastic material properties of magnesium sheets Magnesium alloys show a limited formability at room temperature This results from the fact that the hexagonal crystal structure and the low tendency to twinning only allow limited deformations The differently orientated crystallites only show a deformation on the individual base slip plane which leads to a mutual slip hindrance 4 5 A considerable improvement of the forming qualities can be achieved by applying temperature The considerable increase in formability that occurs in the temperature range from 200 to2258C depending on alloying composition was investigated by Siebel 6 The reason for this effect was found in the thermal activation of pyramid sliding planes in the hexagonal structure 7 2 1 Influence of forming temperature on flow stress A detailed evaluation of the deformation properties of magnesium sheets requires the determination of the material s characteristic values like anisotropy or flow curves 8 9 Because systematic investigations in this area are not available extensive investigations concerning the influence of temperature and strain rate on plastic properties of various magnesium alloys were performed at Institute for Metal Forming and Metal Forming Machine Tools IFUM Fig 1 displays flow curves of magnesium sheet material AZ31B at different temperatures determined in the uniaxial tensile test according to EN 10002 part 5 It is obvious that the stresses and possible strains largely depend on the forming temperature The decrease of flow stresses in the temperature range above 2008C attributes to temperature dependent relaxation 3 3 Deep drawing of magnesium alloys In order to investigate the formability of magnesium sheets deep drawing tests at different forming temperatures were carried out at IFUM with a cylindrical tool system Fig 3 shows the results of deep drawing tests at a temperature of 50C Whereas the deep drawing of the alloy AZ31B using a low drawing ratio of b0 1 45 was possible drawing depth 30 mm the alloys AZ61B and M1 showed early fracture Using drawing ratio of b0 1 6 AZ31B showed fracture similar to AZ61B and M1 These tests confirm the low formability of magnesium alloys at low temperature However the investigated magnesium alloys show very good formability at higher temperature The maximum limit drawing ratio of b0 max 2 52 was detected for AZ31B at a forming temperature of 2008C AZ61B and M1 show maximum values of approximately b0 max 2 20 up to 2 25 The values of the aluminum alloy AlMg4 5Mn0 4 are displayed for 4 comparison Due to the good formability of the aluminum alloy at room temperature the increase in limit drawing ratio with rising temperature is low compared to the magnesium alloys The results gained from the tensile tests showed the significant influence of strain rate on the mechanical properties of magnesium alloys 1 H Kehler et al Partikelversta rkte Leichtmetalle Metall Band 49 Heft 3 1995 2 E Doege K Dro der St Janssen Leichtbau mit Magnesiumknetlegierungen Blechumformung und Pra zisionsschmieden Technischer Mg Legierungen Werkstattstechnik Band 88 Heft 11 12 1998 3 E Doege K Dro der F P Hamm Sheet Metal Forming of Magnesium Alloys Proceedings of the IMA Conference on Magnesium Metallurgy Clermont Ferrand France October 1996 4 H J Bargel G Schulze Werkstoffkunde VDI Verlag GmbH Du sseldorf 1988 5 C S Roberts Magnesium and Its Alloys Wiley New York 1960 6 G Siebel in Beck Ed Technology of Magnesium and Its Alloys Hughes London 1940 7 N N Magnesium and Magnesium Alloys Ullmann s Encyclopedia of Industrial Chemistry Reprint of Articles from 5th Edition VCH Weinheim 1990 8 E Doege K Dro der Processing of magnesium sheet metals by deep drawing and stretch forming Mat Tech 7 8 1997 19 23 9 E Doege K Dro der St Janssen Umformen von Magnesiumwerkstoffen DGM Fortbildungsseminar Clausthal Zellerfeld Oktober 1998 pp 28 30 10 L Taylor H E Boyer in E A Durand et al Eds Metals Handbook 8th Edition Vol 4 American Society of Metals ol 4 American Society of Metals Cleveland OH 1969 11 K Siegert et al Superplastische Aluminiumbleche Verarbeitung mit numerischen Pressen Metall 45 Jahrgang Heft 4 1991 12 E F Emley Principles of Magnesium Technology Pergamon Press Oxford 1966 13 D Schmoeckel Temperaturgefu hrte Proze steuerung beim Umformen von Aluminiumblechen EFB Forschungsbericht Nr 55 1994 14 H Bei wa nger Warmziehen von Leichtmetallblechen Mitteilung 5 der Forschungsgesellschaft Blechverarbeitung Nr 27 1950 15 E Kursetz Die Anwendung von Wa rme bei der Herstellung von Blechformteilen aus Schwer Umformbaren Werkstoffen Ba nder Bleche Rohre Nr 5 1974 16 O Heuel Optimierung der Werkzeugtemperatur Durch Richtige Auslegung und Installation der Temperiersysteme Der Stahlformenbauer Heft 1 1992