Papers by Author: Lennart Stutz

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Authors: Lennart Stutz, Julian Quade, Michael Dahms, Dietmar Letzig, Karl Ulrich Kainer
Abstract: Magnesium alloy sheets bear significant potential in replacing conventional materials such as aluminium and steels in ultra lightweight designs. High specific strength and stiffness, combined with the lowest density of all structural metals make magnesium alloy sheets candidates to face the challenges of reducing vessel weight in the transportation industry and thus, green house gas emissions. For forming components from sheet metal, deep drawing is a well established and commonly applied process. Due to the limited formability of magnesium sheets at room temperature, deep drawing processes have to be conducted at elevated temperatures. In the present study, hot deep drawing experiments on an industrial scale hydraulic press were successfully conducted. Forming was done at moderately low temperatures from 150°C to 250°C. Sheets of the magnesium alloy AZ31B (Mg-3Al-1Zn-Mn) were drawn to symmetrical cups according to Swift. For AZ31, distinct basal type textures are formed during hot rolling. The influence of texture on earing is displayed. The microstructural evolution of the material is dominated by the formation of twins and dynamic recrystallisation. By optimising the process, a drawing ratio of 2.9 was achieved for AZ31 sheet, outperforming conventional materials at ambient temperature.
Authors: Dietmar Letzig, Lennart Stutz, Jan Bohlen, Karl Ulrich Kainer
Abstract: Sheet metal forming experiments have been carried out on AZ31 and ZE10 sheets produced by rolling conventionally DC cast slabs as well as twin roll cast (TRC) strips. Nakajima tests were performed on the various sheet materials over the temperature range from RT to 200 °C using Hasek type samples of specified geometries to generate various strain paths. The strain path data were used to derive the forming limit curves as plotted in forming limit diagrams for the two alloys. The temperature dependence of the sheet formability is discussed in terms of the operating deformation mechanisms and the roles of alloy composition, initial texture and processing history.
Authors: Lennart Stutz, Jan Bohlen, Gerrit Kurz, Dietmar Letzig, Karl Ulrich Kainer
Abstract: The substitution of conventional materials such as aluminium alloys and steels with the lightest structural metal magnesium and its alloys can yield significant weight saving in the transportation industry and hence, reduce vehicle weight and greenhouse gas emissions. Producing magnesium sheets by conventional hot rolling is expensive due to the large number of rolling passes to final gauge and annealing steps at elevated temperatures between the rolling passes. Twin roll casting is a well established processing route for aluminium sheets which can reduce the necessary rolling passes to a bare minimum to reduce the production costs. This process is receiving increasing attention for the production of magnesium sheets. This study reveals first hand results of sheet metal forming experiments on magnesium sheets rolled from twin roll cast strip as well as conventional DC cast slabs. Two different alloys, AZ31 (Mg-3Al-1Zn-Mn) and rare earth element containing ZE10 (Mg-1Zn-RE) were investigated. It is known that these alloys show significant differences in the microstructure development during conventional rolling as a result of recrystallisation. For hot rolled AZ31, distinct textures are formed with the majority of basal planes oriented in the sheet plane and hence, unfavourably for basal slip. Conventionally rolled ZE10 commonly shows a much weaker texture. Forming limit diagrams are presented and discussed with respect to the initial texture of the sheets. Strain response to various strain paths and plastic anisotropy are evaluated. Results of twin roll cast sheets are compared with conventionally hot rolled sheet of the same alloys. Competitive formability can be achieved at 200°C for all tested sheets. While conventionally rolled sheets show a generally higher formability than their twin roll cast counterparts, ZE10 outperforms AZ31 for both processing routes.
Authors: Joachim Wendt, Boris Bronfin, Lennart Stutz, Gerrit Kurz, Sabrina Schmitt, Menachem Bamberger, Dietmar Letzig
Abstract: Currently magnesium alloys are used for different applications in the transportation industry where cast magnesium alloys dominate the market. Although cast alloys predominate over wrought products such as extrusions, forgings, sheet and plate, the latter are also being used in a variety of different applications. Recently, a growing interest in the automotive industry in looking at potential applications for magnesium turned back towards wrought alloys. Typically, applications of magnesium sheets are sought in automotive or aeronautics industry. However, the spectrum of potential applications can be significantly expanded. For example, body protection systems for civil services like police, custom officers and prison personnel currently include anatomically shaped aluminium alloy sheets. Replacement of aluminium alloys by magnesium to result in substantial weight savings up to 30%.
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