Paper Titles
Microstructure Refinement of Al-Si Alloy Using Compressive Torsion Processing
p.1441
The Important Role of Dissolved Elements (Mn, Fe) in the Process of Rolled Products and Their Effects on Final Properties
p.1447
Modelling Microstructure and Properties: The Contributions of Grain Size, DAS and Bifilms
p.1453
Understanding T-Ingot Horizontal DC Casting Using Process Modelling
p.1461
Continuous Cooling Transformation (CCT) Diagram of Aluminium Alloy Al-4.5Zn-1Mg
p.1467
Application of a Mathematical Model to Simulate Multi-Pass Hot Rolling of Aluminium Alloy AA5083
p.1473
Effect of Hot-Extrusion Conditions on Mechanical Properties and Microstructure of P/M Al-Zn-Mg-Cu Alloys Containing Zr
p.1479
Aging Behaviour of Aluminium Alloys after Severe Plastic Deformation
p.1485
Historical Evolution of Thermomechanical Processes Applied to Aluminium Alloys
p.1493

Continuous Cooling Transformation (CCT) Diagram of Aluminium Alloy Al-4.5Zn-1Mg

Article Preview

Abstract:

Age hardening is one of the most important processes to strengthen aluminium alloys. It usually consists of the steps solution annealing, quenching and aging. For heat treatment simulations as well as for the appropriate choice of quenching processes in heat treatment shops, knowledge of the temperature- and time-dependent precipitation behaviour during continuous cooling is required. Quenching should happen as fast as necessary to reach high strengths, but also as slow as possible, to reduce residual stresses and distortion. This optimal quenching rate of an aluminium component depends on its chemical composition, initial microstructure and solution annealing parameters as well as on its dimensions. Unfortunately continuous cooling transformation (CCT) diagrams of aluminium alloys do almost not exist. Instead isothermal transformation (IT) diagrams or given average quenching rates are used to estimate quenching processes, but they are not satisfying neither for heat treatment simulations nor for heat treatment shops. Thermal analysis, especially Differential Scanning Calorimetry (DSC) provides an approach for CCT-diagrams of aluminium alloys, if the relevant quenching rates can be realized in the DSCequipment. The aluminium alloy Al-4.5Zn-1Mg (7020) is known for its relatively low quenching sensitivity as well as for its technical importance. The complete CCT-diagram of 7020 with cooling rates from a few K/min to some 100 K/min has been recorded. Samples have been solution annealed and quenched with different cooling rates in a high speed DSC. The resulting precipitation heat peaks during cooling have been evaluated for temperature and time of precipitation start, as well as their areas as a measure for the precipitate amount. Quenched samples have been further investigated regarding their microstructure by light and electron microscopy, hardness after aging and precipitation behaviour during re-heating in DSC. The CCT-diagram correlated very well with the microstructure, hardness and re-heating results. A critical cooling rate with no detectable precipitation during continuous cooling 155 K/min could be determined for 7020. A model to integrate the CCT-diagram in heat treatment simulation of aluminium alloys is under development.

You might also be interested in these eBooks
Aluminium Alloys 2006 - ICAA10 View Preview

Info:

Periodical:

Materials Science Forum (Volumes 519-521)

Pages:

1467-1472

DOI:

https://doi.org/10.4028/www.scientific.net/MSF.519-521.1467

Citation:

Cite this paper

Online since:

July 2006

Authors:

O. Kessler, R. von Bargen, Fabian Hoffmann, H.W. Zoch

Keywords:

AA7020 Aluminium Alloy, Al-4.5Zn-1Mg, CCT, Continuous Cooling Transformation Diagram, Differential Power Scanning Calorimetry, DPSC

Export:

RIS, BibTeX

Price:

Permissions CCC:

Request Permissions

Permissions PLS:

Request Permissions

Сopyright:

© 2006 Trans Tech Publications Ltd. All Rights Reserved

Share:

Citation:

References

[1] Altenpohl, D.: Aluminium und Aluminiumlegierungen (Springer Verlag, Berlin 1965).

Google Scholar

[2] Aluminium Taschenbuch (Aluminium-Verlag, Düsseldorf 1988).

Google Scholar

[3] ASM Handbook Vol. 4: Heat Treating (ASM, Metals Park, Ohio, USA 1991).

Google Scholar

[4] Herding, T., Kessler, O., Hoffmann, F., Mayr, P.: Mater. Sci. Forum Vol. 396-402 (2002) 2, pp.869-874.

Google Scholar

[5] Ryum, N.: Zeitschrift Metallkunde, Vol. 66 (1975), pp.338-346 & pp.377-388.

Google Scholar

[6] Utschick, H.; Schultze, D.; Böhme, K.; Methoden der thermischen Analyse (CLB Chemie in Labor und Biotechnik 45, offprint for Bodenseewerke Perkin-Elmer GmbH, 1994).

Google Scholar

[7] Jiang, X.J.; Noble, B.; Holme, B.; Waterloo, G.; Tafto, J.: Metallurgical and Materials Transactions A Vol. 31 (2000) A, pp.339-348.

Google Scholar

[8] Jiang, X.J.; Noble, B.; Hansen, V.; Tafto, J.: Metallurgical and Materials Transactions A Vol. 32 (2001) A, pp.1063-1073 Acknowledgement The authors thank Deutsche Forschungsgemeinschaft for funding the work (DFG KE 616/9-1).

Google Scholar