Thermal Stability of Al-Cu-Mg Alloys

Abstract:

The Al-Cu-Mg alloys currently used at elevated temperature for aerospace applications, such as 2618 and 2219, were developed in the 1950s. Since then, not only have property requirements evolved significantly with the widespread introduction of damage tolerant design, but also the understanding and modelling capacity of the alloys' property-composition-processing relationships have developed beyond recognition. Moreover there is a renewed need for higher strength/toughness, higher temperature solutions in many aircraft's hot areas.A kinetic model has been developed to predict the strengthening capability and the thermal stability of hardening phases. It is based on a homogeneous nucleation, growth and coarsening model applied to S' (Al₂CuMg) and θ' (Al₂Cu); the yield strength is then calculated from the precipitates' size distribution. It suggests two areas of interest in the Al-Cu-Mg diagram.Three targeted compositions were then explored inside and outside the areas of interest and their thermal stability assessed up to 250°C. Different behaviours were observed and are explained by the strengthening potential and the coarsening resistance of S' and θ'. The two interesting areas for thermally stability are confirmed. An area of poorer thermal stability was also identified, associated with a high Cu content in solid solution which accelerates precipitate coarsening kinetics.

• Periodical: Materials Science Forum (Volumes 794-796)
• Pages: 691-696
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.794-796.691
• Online since: June 2014
• Authors: Gaelle Pouget*, Christophe Sigli
• Keywords: AA2000, Al-Cu-Mg Alloys, Coarsening, High Temperature Alloy, Thermal Stability

References

[1] J.G. Kaufman, Properties of aluminum alloys: tensile, creep, and fatigue data at high and low temperatures, ASM International, (1999).

[2] I.J. Polmear, M. J Couper, Design and development of an experimental wrought aluminum alloy for use at elevated temperatures. Metall. Trans. 19A (April 1988) 1027-1035.

DOI: 10.1007/bf02628387

[3] J.M. Silcock, T.J. Heal, H.K. Hardy, Structural ageing characteristics of binary Aluminium-Copper alloys. J. Inst. Metals 82 (1953-54) 239-248.

[4] J.M. Silcock, The structural ageing characteristics of Al-Cu-Mg alloys with Copper: Magnesium weight ratios of 7: 1 and 2, 2: 1. J. Inst. Metals 89 (1960-61) 203-210.

[5] S.C. Wang, M.J. Starink, Precipitates and intermetallic phases in precipitation hardening Al–Cu–Mg–(Li) based alloys. Int. Mater. Rev. 50 (2005) 193-215.

DOI: 10.1179/174328005x14357

[6] C. Sigli, Nucleation, Growth and Coarsening of Spherical Precipitates in Aluminum Alloys. Mater. Sci. Forum 331–337 (2000) 513-518.

DOI: 10.4028/www.scientific.net/msf.331-337.513

[7] C. Sigli, Development of a new 7xxx ageing model. Mater. Sci. Forum 519-521 (2006) 321-326.

DOI: 10.4028/www.scientific.net/msf.519-521.321

[8] G.C. Weatherly, R.B. Nicholson, An electron microscope investigation of the interfacial structure of semi-coherent precipitates. Philos. Mag. 17 (1968) 801–831.

DOI: 10.1080/14786436808223031

[9] R.N. Wilson R, J.E. Forsyth, Effects of additions of 1% Iron and 1% Nickel on the age-hardening of an Al-2. 5Copper-1. 2Magnesium alloy. J. Inst. Metals 94 (1966), 8-13.

[10] National Research Council, Accelerated aging of materials and structures: the effects of long-term elevated-temperature exposure. National Materials Advisory Board (NMAB-479), National Academy Press, Washington D.C. (1996).

DOI: 10.17226/9251