Papers by Author: Jan Bohlen

Abstract: Commercial magnesium alloys such as AZ31 exhibit strong crystallographic textures during massive deformation such as rolling. A randomisation of the texture, however, was found in alloys with rare earth (RE) elements in solid solution. This paper describes the development of microstructure and texture during rolling of the Al-free RE-containing wrought magnesium alloy ZEK100 during hot rolling. This alloy develops a strong texture with a pronounced component towards the transverse direction (TD) of the sheets. This TD component forms already after the first rolling pass, persists through all following passes and is further enhanced by subsequent heat treatment. These results are contrasted with results from a study on texture development of binary RE containing Mg-alloys, which show that the presence of RE elements alone is not responsible for the tilt of basal planes towards the TD. There is, however, a threshold concentration at which the texture begins to weaken.

Abstract: The influences of rare earth elements addition on the crystallographic texture and microstructural evolutions are examined during rolling and annealing of Mg-sheets. In case of Nd or Y additions, dynamic recrystallisation is suppressed such that the deformed microstructure is observed after hot rolling with relatively large strain per pass. Cold rolled binary Mg-Nd alloy sheet shows strong texture with splitting of the basal poles in the rolling direction, however, the texture intensity decreases significantly during the recrystallisation annealing. From the comparison of deep drawing behaviours between commercial ZE10 and AZ31 sheets, it is observed that the addition of the rare earth elements and accompanying texture changes result in the improved formability.

Abstract: A yield function for hexagonal closed packed (hcp) metals was modified with respect to strain rate and temperature and developed to capture the material behaviour during extrusion. Magnesium alloy ZEK100 was extruded indirectly at 300°C into a round bar. Compression tests were carried out at various strain rates, temperatures and sample orientation to characterise the material flow. These data were used as input data for fully thermo-mechanical coupled simulations of indirect extrusion. A successful prediction of the extrusion force and the temperature increase during extrusion is presented.

Abstract: While magnesium cast components have found their application in the transportation industries the interest is now spreading to wrought alloys due to the possibility to get even more homogeneous and better properties compared to cast parts. Therefore alloy and process development especially for extrusion is a main concern to enhance the application of Magnesium wrought alloys. This paper gives an overview on the actual status of the process and alloy development of extruded Magnesium wrought alloys.

Abstract: In view of the increasing needs for efficient usage of natural resources and environmental protection in our modern society, weight reduction in transportation such as cars, trains or aircrafts is of fundamental interest. In order to solve this major issue, improved concepts are necessary which also emphasize the usage of light weight materials in construction. Especially magnesium and its alloys as the lightest available constructional metals have a major potential in this regard. Since magnesium cast components have found their application, interest is now spreading towards wrought alloys for use as structural components. However, the use of wrought magnesium alloys in the transportation industry is still limited at present. In this paper we give an overview on the present state of the art as well as on specific requirements for the processing of wrought magnesium alloys. We will show the technical potential in terms of improved economic aspects for wrought magnesium and discuss research topics such as process-specific alloy design.

Abstract: The crystallographic response to deformation – texture evolution, internal elastic strain, and twin evolution – was measured for three load/orientation variants for AZ31 magnesium alloy extrudate tested in-situ in a synchrotron beamline. Specimens were loaded in tension parallel to the extrudate transverse direction, in compression along the same axis, and in compression parallel to the extrudate normal direction. The crystallographic responses are correlated with the mechanical behaviour of the extrudate.