Papers by Author: Knut Marthinsen

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Authors: Knuter E. Snilsberg, Ida Westermann, Bjørn Holmedal, Odd Sture Hopperstad, Y. Langsrud, Knut Marthinsen
Abstract: In the present work, three-point bending tests have been performed on four commercially extruded 6xxx- and 7xxx alloys, one with a fibrous and one with a recrystallized grain-structure for each alloy class, with the bending axis orientated 0, 45 and 90° with respect to the extrusion direction. Microstructure and texture characterization as well as tensile testing of the same materials have been performed and correlated with the bending results. In general there is good agreement between the bending angle and the fracture strain for all alloys, with the highest values in the extrusion direction. However, there are no indications in the microstructure and texture that explain the large differences in bendability observed. Die lines and recrystallized layer on a fibrous alloy have been removed to investigate their effect on the bending behaviour. However, these effects also seem to be limited, and cannot explain the anisotropy effects observed in bending angles.
Authors: Michal Kolar, Katharina Teichmann, Sverre Gulbrandsen-Dahl, Ketill Olav Pedersen, Knut Marthinsen
Abstract: In the present work we report on the effect of pre-deformation followed by/together with artificial aging on the mechanical properties as strength, ductility and work hardening of an Al-Mg-Si alloy (AA6060). The AA6060 alloy was initially cast, homogenized and extruded according to standard industrial practice. The extruded material was then subjected to a solution heat treatment and subsequently artificially aged after (sequential mode) and during (simultaneous mode) various combinations of deformation (0-10%) and heat treatments. The aging behaviour and mechanical properties have been characterized in terms of Vickers hardness and tensile testing. It is found that small, even very small, pre-deformations strongly affect the aging behaviour and associated tensile properties. Moreover, it is found, that with the carefully chosen parameters of simultaneous deformation and aging one can reach mechanical properties superior to those following pre-deformation and subsequent aging (sequential mode). The results are compared and discussed in view of differences in processing conditions and microstructure characteristics.
Authors: Egil Fjeldberg, Knut Marthinsen
Abstract: In the present work computer simulations using a 3-D Potts Monte Carlo model are demonstrated and discussed as a tool to study the effects of a number of parameters related to the deformation conditions as well as process and material parameters related to the nucleation and growth conditions of recrystallisation, such as e.g. second phase particles, which may influence the kinetics and texture of recrystallisation. The MC simulations have been combined with a deformation texture model to provide the deformation structure from which the recrystallisation nucleates and models which provide the relative proportions of certain nucleation mechanisms and their orientation spectrum. All together this gives a simulation tool which allows for a multitude of numerical experiments and the possibility to study parameter relationships which are often not easily available from experiments. The potential of such a simulation tool is discussed in terms of a few generic examples.
Authors: Knut Marthinsen, Bjørn Holmedal, Shahriar Abtahi, Randulf Valle, S. Chen, Erik Nes
Authors: R. Morgenstern, M. Videm, Knut Marthinsen, Erik Nes, Trond Furu
Abstract: The starting material, the deformed state, as well as the recrystallised microstructure and texture have been analysed as a function of Zener-Hollomon parameter and strain for two differently heat-treated AlMgSi alloys, deformed in torsion. An interesting and somewhat surprising observation is that the grain size was always higher in the material heat treated to form large Mg2Si particles. Moreover, no indications of PSN effects were observed in any of the materials, even at the highest Zener-Hollomon parameters. This observation was quite unexpected as the highest Zener-Hollomon parameters were well above the typical critical level for which significant PSN effects have been observed in similar alloys. The results have been carefully analysed and possible explanations are discussed.
Authors: Håkon Hallem, Børge Forbord, Knut Marthinsen
Abstract: In the present work the precipitation behaviour and recrystallisation resistance of Alalloys containing Hf, Sc and Zr in different concentrations and combinations have been investigated. Special focus has been put on the Hf-containing alloys, as one of the objectives of this work was to find out if Hf can be used as a replacement for Sc. Additions of Sc, either alone or in combination with Zr, leads to the formation of coherent and homogeneously distributed dispersoids, which very efficiently inhibit recrystallisation. Despite these attractive properties, the high price of Sc has limited its use as an alloying element in aluminium. The present investigation has revealed that Hf cannot fully replace Sc, as only heterogeneous dispersoid distributions are obtained in the absence of Sc, i.e. in regions where the number density is low the alloys would still be prone to recrystallisation. However, as an extra addition to the already remarkably stable Sc+Zr-containing alloys, Hf can lead to further improvements and consequently open for the use of aluminium alloys at very high temperatures. Al3(Sc,Zr,Hf)-dispersoids were present at the largest f/r-ratios and also displayed lower coarsening rates than Al3(Sc,Zr)-dispersoids. Very promising results were obtained for an Al-Hf-Sc-Zr alloy, which maintained mainly an unrecrystallised structure after extrusion and large degrees of cold rolling.
Authors: Tanja Pettersen, Yan Jun Li, Trond Furu, Knut Marthinsen
Abstract: During casting and homogenisation of aluminium the microstructural fundament for further processing is made. Particle structure (dispersoids and primary particles), grain structure and level of elements in solid solution govern the mechanical and annealing properties of the material. In 3xxx-alloys, Mn in solid solution and Mn-containing dispersoids formed during homogenisation play an important role in controlling the recrystallization behaviour of the material [e.g. 1, 2, 3]. Other elements, such as Si, will have an influence on the formation of dispersoids [4, 5]. Hence, to control the annealing behaviour of the material, it becomes important to control the particle structure. In the present investigation, an AA3103 alloy, and modified versions of this alloy, have been investigated. Various homogenisation treatments have been performed and the resulting material has been studied. Electrical conductivity has been measured and microstructural investigations have been carried out.
Authors: Sverre Gulbrandsen-Dahl, Calin D. Marioara, Ketill Olav Pedersen, Knut Marthinsen
Abstract: In the present study, several Al-Mg-Si alloys have been studied with respect to microstructure characteristics, i.e. particle statistics, and resulting mechanical properties. The alloys and tempers represents a wide range of type of hardening particles stretching from pre-β’’, via β’’, to post-β’’ particles such as β’, U1, U2 and B’, and various sizes, number densities and volume fractions of these particles. The correlation between volume fraction of hardening precipitates and mechanical strength is strong within alloys with pre-β’’ and β’’ as the main hardening precipitates, but this correlation does not fit for alloys with post-β’’ precipitates. However, a strong correlation between mechanical strength and both number density and cross-section area of the hardening precipitates is found, independent of type of precipitate. The consequences of these correlations are discussed with respect to proposed hardening models found in the literature.
Authors: Hans Erik Vatne, Frank Perocheau, Hans Erik Ekström, Laurent Poizat, Kathrin Nord-Varhaug, Knut Marthinsen, Eva Lindh, Joacim Hagström, Trond Furu
Authors: Sverre Gulbrandsen-Dahl, Knut E. Moen, Flemming J.H. Ehlers, Calin D. Marioara, Ketill Olav Pedersen, Knut Marthinsen
Abstract: Standard and high resolution transmission electron microscopy (TEM) and advanced post processing of the TEM images have been applied for quantitative characterization of the hardening particle structure of an Al-Mg-Si alloy optimized for formation of the metastable phase β’. The relation between the structural characterization and the mechanical properties has been developed. A first attempt is presented on visualization and quantification of the coherency strain field of β’, based on a combination of Vienna Ab-initio Simulation Package (VASP) calculations and continuum mechanical modelling.
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