Papers by Keyword: Recrystallisation Resistance

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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: Håkon Hallem, W.J. Rittel, Børge Forbord, Knut Marthinsen
Abstract: A high recrystallisation resistance is required in aluminium alloys intended for processing or use at temperatures between 450°C-600°C. Additions of Hf, Sc and Zr significantly improve the resistance to recrystallisation through the formation of Al3X-dispersoids (X=Hf,Sc,Zr), and in this work different concentrations and combinations of these elements were added to five aluminium alloys. The alloys were extruded, subjected to various degrees of cold rolling (0%-80%) and finally annealed at high temperatures in order to study the structural stability. All variants displayed a high resistance towards recrystallisation, but the best results were obtained in the alloy containing only Sc and Zr. In this alloy no signs of recrystallisation were observed even after 1 hour annealing of extruded and 80% cold rolled profiles at 600°C.
Authors: Vladivoj Očenášek, Bohumil Smola, Ivana Stulíková, J. Pelcová
Abstract: The present contribution deals with the effect of thermal and mechanical treatment on structure, mechanical and physical properties of as cast, cold and hot worked AlMg3 type alloy produced by conventional casting, as well as by powder metallurgy. The properties of the AlMg3 alloys with additions of Sc and Zr in the weight concentration ranges 0.14 – 0.29% and 0.05 – 0.12% respectively were studied and compared with those of the alloys without Sc and Zr additions. The anti-recrystallization effect, phase development and mechanical properties investigated in the course of isothermal as well as isochronal annealing were studied by using optical and transmission electron microscopy, electrical resistometry and hardness measurements. The parameters of technological procedure of optimum age hardening by the Al3(ScxZr1-x) phase are presented. This optimum can not be reached if the as cast alloy is exposed to temperatures higher than 350°C. Even the small additions of Sc such as 0.15 wt. % ensure the anti-recrystallization effect of Al3(ScxZr1-x) phase.
Authors: Børge Forbord, Håkon Hallem, Knut Marthinsen
Abstract: As cast and precipitation annealed variants of Al-Mn-Zr-alloys with and without Sc have been extruded in order to study the effect of Sc on the extrudability and the recrystallisation resistance after extrusion and subsequent annealing. Both Zr and Sc form dispersoids, which retard recrystallisation very effectively in many aluminium alloys. However, while Al3Zr often is heterogeneously distributed, a dense and homogeneous distribution of Al3(Sc,Zr)-dispersoids is obtained when Sc is added. This was also the case in these alloys, and the Sc-containing variants consequently displayed a far higher recrystallisation resistance than the Sc-free variants during extrusion and subsequent annealing. Another advantage by adding Sc is that precipitation annealing no longer seems to be necessary in order to obtain a high recrystallisation resistance, as the Sccontaining variants displayed an identical structural stability. The Sc-free alloy, on the other hand, had to be precipitation annealed in order to be able to resist recrystallisation during extrusion. However, an addition of Sc leads to a lower extrudability, as the Sc-containing variants displayed significantly higher extrusion pressures than the Sc-free alloys.
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