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Micro-Doping of Aluminum-Lithium Alloys

#2622


Micro-Alloying of Aluminum-Lithium Alloys and Optimization of Thermal Treatment Conditions

Tech Area / Field

  • MAT-ALL/High Performance Metals and Alloys/Materials

Status
3 Approved without Funding

Registration date
14.10.2002

Leading Institute
All-Russian Institute of Light Alloys, Russia, Moscow

Supporting institutes

  • MISIS (Steel and Alloys), Russia, Moscow

Collaborators

  • Airbus Deutschland GmbH, Germany, Munich\nIstituto Materiali Speciali per Electronica e Magnetismo, Italy, Parma\nTokyo Institute of Technology / Department of Metallurgy and Ceramics Science, Japan, Tokyo\n[Individual specialist]

Project summary

Al-Li-alloys have unique combination of properties – high static and dynamic strength with low density, high elasticity modulus and good welding (i.e. Al-Mg-Li – alloys). The alloys are widely applied in aircraft- and space-industry. Scientists suppose they will substitute a large number of all Al-alloys used in aircraft industry. Meanwhile Al-Li alloys are restricted in application for instability and anisotropy of properties in semi-bars (for example, in plates and sheets).

Reduction of these disadvantages is aim of the present work. The aim will be achieved by:

– alloying of aluminum-lithium alloys by additions of scandium and zirconium;


– development of special technological conditions of strengthening thermal treatment.

For successful decision of this problem, it is necessary to develop effective methods of introduction of scandium accompanying with zirconium into aluminum melt. The method must guarantee introduction of additions into aluminum solid solution.

Strength properties of heat-reinforced Al-alloys are determined by the joint action of the following factors:

– solid solution strengthening (hardening);


– dispersed strengthening;
– structure reasons of strengthening; this kind of strengthening is result of existing non-re-crystallized (polygonization state) structure after heat treatment.

For Al-Li alloys the last factor has tremendous influence. Stable structural strengthening in Al-Li semi-bars allow to increase and getting more stable their properties.

Production of Al-Li semi-bars with non-recrystallized (polygonization state) structure depends on small additions of transition metals.

The project includes the following:

– research of correlation between Zr-content vs structure and properties of Al-Cu-Li semi-products. Zr presents practically in all Al-alloys (~0.1%), but small variations of Zr-content may change structure and properties of the final product drastically;


– investigating small additions of Sc (~0.01%) itself and in combination with Zr on structure and properties of Al-Mg-Li semi-bars; investigating kinetic of formation and decay of solid solution of Li and Sc in Al as well as phases precipitated in the process of decay;
– describing general regularity of process of recrystallization for Al-Li-Mg alloys with small additions of Sc and Zr;
– finding the most effective parameters for intermediate annealing (between cold rollings) to improve plasticity, homogeneity of local deformations and as a result to reduce anisotropy along a sheet;
– elaborating parameters of aging thermal treatment that in general reduces anisotropy along a sheet.

The final product will be a report with recommendations on the following subjects:

– alloying typical Al-Mg-Li and Al-Cu-Li alloys with small additions of Sc and Zr that ensure non-recrystallization structure (polygonization state) in hot- and cold treated semi-bars; as a result it improves mechanical properties of hot-treated semi-bars and increases strength of cold-treated ones;


– parameters of heat treatment resulting in decreasing anisotropy in Al-Mg-Li sheets.

Methodological scheme of implementation of the project is following. After literature observation, summary of own experience and equipment preparation, the first cycle of melting and casting of Al-Li alloys will be carried out in laboratory conditions. Specimens of alloys will be under controlling during all technological operations. Structure will be investigated by optical, scanning electron and transmission electron microscopy; x-ray methods will be used as well. Auger-spectroscopy will be used for determination of distribution of micro-additions inside alloys. Ingots will be treated by deformation and thermal treatment. On the base of obtained laboratory results, producing semi-industrial ingots will be carried out. Various kinds of semi-products will be manufactured on the basis of developed methods.

The base expected results of the project are:

– Increasing strength parameters of plates and sheets, produced by developed methods, not less than at 15%;


– Development of methods of introduction of micro-additions of scandium and zirconium into alloys of systems Al-Mg-Li and Al-Cu-Li;
– Database on mechanical properties and characteristics of structure of alloys system Al-Mg-Li and Al-Cu-Li in dependence from consist of micro-additions of scandium and zirconium;
– Reduction of anisotropy of mechanical properties of plates and sheets in several times (for example, anisotropy of elongation decreases in 3-4 times);
– Development of technological conditions of thermal treatment for cardinal decreasing anisotropy of properties of sheets from Al-Mg-Li alloys;
– Recommendation on alloying of typical alloys of systems Al-Mg-Li and Al-Cu-Li by small additions of scandium and zirconium;
– Pilot specimens of semi-products from developed materials.


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