Papers by Author: Karl Ulrich Kainer

Abstract: The development of new Mg-Sn based alloys that have shown improved corrosion resistance needs further investigations to develop standard alloys for industrial use. In the present study, the influence of heat treatment was investigated by examining the creep resistance of Mg-Sn and Mg-Sn-Ca alloys at 85 MPa under 135 °C identify the best conditions to improve the mechanical properties of such alloys. Additionally, the changes in microstructure of these alloys were studied and analysed by light microscopy, X-ray diffraction and scanning electron microscopy. It was found that the heat treatments can affect the microstructure of the binary alloy while no apparent change in the microstructure was found in the Mg-Sn-Ca alloys, indicating that the second phase CaMgSn is thermal stable in this alloy. Based on the obtained results, the relationship between the microstructure and creep behaviour are discussed.

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: Magnesium applications for structural components in the automotive industry are constantly rising. This is based on the recent development of new alloys, new fabrication processes, and the ambition of car manufacturers to reduce the vehicles weight and CO2 emissions according to the EU and US policy [1, 2]. A rising quantity of magnesium per vehicle leads to a rising quantity of scrap which needs to be recycled according to the European Directive on end-of life vehicles [3]. So far post consumer scrap has not been used for structural parts. But since the metal is still expensive compared to aluminium or steel, and remelting saves more than 90 % of the energy for primary production, magnesium recycling will significantly contribute to cost savings. In comparison to steel or aluminium a recycling cycle for magnesium has not yet been established. Concerning post consumer scrap it is likely that many vehicles will end up in the shredder fraction or at least will be mixed up instead of being dismantled and separated according to their alloy. Thus it is reasonable to define secondary alloys which allow the use of post consumer scrap for structural applications. Creep resistant alloys have the potential of a broad application concerning the weight of the components and therefore a secondary alloy would be reasonable. The aim of this work is to examine a row of AM50-based alloys, modified with additions of Sr, Ca, and Si due to the importance of these elements to increase creep resistance and their usage in modern magnesium alloys. The corrosion properties as well as the mechanical properties and microstructures are investigated in the as-cast and annealed condition. Salt spray tests (using 5 % NaCl) and electrochemical corrosion methods are applied to investigate the corrosion properties which are then compared to the unmodified AM50. Tensile and compression tests at temperatures ranging from 20 °C to 200 °C are applied to investigate the mechanical properties.

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.

Abstract: The texture influence on the mechanical behavior during uniaxial tension was studied in AZ31 (Mg – 3 Al – 1 Zn in wt.%), one of the common wrought Mg alloys. Since three tensile samples were cut in 0°, 45°, 90° to the extrusion direction, the initial bar texture influences on the mechanical behavior differently. In-situ texture measurements were carried out using hard X-rays under loading condition. According to the initial texture loading results in a variation of the mechanical behavior (yield strength, ultimate tensile strength and strain hardening rate) and in different final textures. The different texture development in each sample relates directly to the activation of different deformation systems, which is strongly influenced by the initial texture

Abstract: Thixocasting is a new semi-solid processing route for magnesium alloys; it is claimed that finer microstructures can be produced and as a consequence, better corrosion resistance can be achieved. Therefore, it is of great interest to compare the corrosion properties of two Mg-Zn-RE alloys produced by standard squeeze casting and new semi-solid casting technique. The influence of the two different processing routes and the replacement of rare earth elements by Ca additions on the corrosion behavior were studied in NaCl aqueous solutions by (a) analyzing the corrosion morphology, (b) measuring electrochemical polarization curves, and (c) carrying immersion tests at constant pH-value. Using light microscopy, scanning electron microscopy and X-ray diffraction, the corrosion results were related to the microstructures on the specific alloys. The results indicate that Ca cannot replace rare earth elements under corrosion aspects, but they also showed that the thixocasting process resulted in better corrosion resistance.