Papers by Author: Karl Ulrich Kainer

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Authors: Yuan Ding Huang, Xiu Hua Zheng, Anopuo Okechukwu, Gyu Seok Kim, Karl Ulrich Kainer, Norbert Hort
Abstract: A homogeneous microstructure of as-cast magnesium alloys is necessary to improve the formability during their subsequent thermomechanical processing. In Al-containing magnesium alloys, the grain refinement by carbon inoculation is considered to be the best approach until now. However, the mechanism of grain refinement is unclear. The present work investigates the coring microstructure in Mg-Al alloys inoculated with carbon using FIB, SEM and TEM techniques. In each grain one or more “hillocks” exist, enriched with carbon, manganese and aluminium. This is possibly related to the inhomogeneous nucleation of alpha-magnesium. The precipitates in these “hillocks” are always surrounded by the aluminium-rich zones. These characteristics of microstructure observed in Mg-Al alloys with carbon inoculation are compared with that observed in Al-free magnesium alloys inoculated by zirconium. The similarities between them are discussed. A novel mechanism is suggested to explain the grain refinement in Mg-Al alloys inoculated by carbon.
Authors: F. Kaiser, Dietmar Letzig, Jan Bohlen, A. Styczynski, Ch. Hartig, Karl Ulrich Kainer
Authors: Carsten Blawert, Emma D. Morales, Wolfgang Dietzel, Karl Ulrich Kainer
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.
Authors: B.L. Mordike, Karl Ulrich Kainer
Authors: Emma D. Morales, Edward Ghali, Norbert Hort, Wolfgang Dietzel, Karl Ulrich Kainer
Authors: Vàclav Sklenička, M. Pahutová, K. Kuchařová, Milan Svoboda, Karl Ulrich Kainer
Authors: J. Göken, J. Swiostek, Dietmar Letzig, Karl Ulrich Kainer
Abstract: Magnesium cast parts as well as indirectly and hydrostatically extruded profiles were used in order to investigate the influence of different microstructures on the damping behaviour of magnesium AZ-alloys. Especially, hydrostatic extrusion leads to a significant grain refinement in the extruded profile compared to indirect extrusion. Strain dependent damping measurements were carried out at room temperature using alloys AZ31, AZ61 and AZ80. Damping was determined as the logarithmic decrement of free bending beam vibrations. The results of these measurements after indirect and hydrostatic extrusion are shown and discussed.
Authors: Daniel Fechner, Petra Maier, Norbert Hort, Karl Ulrich Kainer
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.
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