Thermodynamics-Based Computational Design of Al-Mg-Sc-Zr Alloys
- PDF / 454,635 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 50 Downloads / 181 Views
ON
WHILE it has been experimentally documented[1–3] that additions of Sc or combinations of Sc and Zr can raise significantly the yield strength of Al-Mg alloys, a sound thermodynamic analysis that would allow the design of these alloys is not available. This article presents a computational thermodynamics-based method for assessing the effects of combined Sc and Zr additions on the grain refinement and recrystallization resistance of Al-Mg alloys. The method can be used for the selection of the optimum alloy variants, in an effort to reduce the time and costs related to the traditional empirical alloy development methodologies. Non-heat-treatable aluminum alloys are utilized in all of the major industrial markets for aluminum flat-rolled products. Transportation, packaging, and the building/ construction sectors represent the largest usage of nonheat-treatable sheet. Among them, wrought non-heattreatable Al-Mg alloys are used, rather widely, as a structural material due to their good weldability, excellent corrosion resistance, and ductility. Recently there has been an increasing interest in Al-Mg alloys in the form of hot-rolled thick plates (8 to 15 mm) for marine applications. However, even alloys containing 5 to 6 pct Mg do not show adequate strength. These alloys are strengthened mainly by solid-solution strengthening
G.N. HAIDEMENOPOULOS, Professor, and H. KAMOUTSI, Research Associate, are with the Laboratory of Materials, Department of Mechanical Engineering, University of Thessaly, Volos, Greece. Contact e-mail: [email protected] A.I. KATSAMAS, formerly Research Associate, Laboratory of Materials, Department of Mechanical Engineering, University of Thessaly, is with the Directorate of Environment and Land Planning, Region of Thessaly, Larissa, Greece. Manuscript submitted October 1, 2009. Article published online February 5, 2010 888—VOLUME 41A, APRIL 2010
from the Mg atoms and work-hardening during cold rolling. However, in hot-rolled products in which the work-hardening contribution is negligible, additional alloying is needed in order to improve the mechanical strength of the alloys. As already mentioned, there has been sound experimental evidence that Sc and Zr additions raise the yield strength of Al-Mg alloys. The strengthening mechanisms have been discussed[4,5] and it is clear that the strength improvements obtained are mainly due to the following: (1) grain refinement of the as-cast structure (modification effect)[2] and (2) inhibition of recrystallization during hot working.[6] Precipitation strengthening[4] has also been considered; however, its contribution is not as strong as the previous two mechanisms. All these effects are activated by the formation of fine dispersions of Al3Sc (in the case of alloying with Sc) and Al3Sc/Al3Zr or Al3(ScxZr1–x) (in the case of alloying with Sc and Zr) intermetallics. In the Al-Mg-Sc-Zr system under consideration, it has been found that the Al3Sc phase dissolves approximately 12 at. pct Zr, which corresponds to the substitution of almost 50 pct of the Sc lattice sites.
Data Loading...
