Abstract
In recent years, a creep model that does not involve adjustable parameters has been successfully applied to coarse-grained aluminum. The main feature of this model is that it is fully predictable. On the other hand, in the case of age-hardenable alloys, any physically-based creep model should take into account the changes in the volume fraction, size and distribution of strengthening precipitates, and the effect of grain size. With this aim in view, in this paper, the original model previously applied to single phase-alloys has been modified to describe the effects of the grain size and of the consequences of the high-temperature exposure on the strengthening role of precipitates. To this end, phenomenological equations describing the coarsening phenomena and their dependence on the applied stress have been introduced. The modified model has given an excellent description of the experimental behavior of an AA2024-T3 alloy tested at 250 and 315 °C and has provided a sound explanation of the difference observed when comparing the minimum creep rate obtained using two different testing techniques.
Highlights
AA2024 (Al-4%Cu-1.5%Mg) Aluminum alloy is one of the most widely used materials for airplane structures [1,2,3], and, as a result, has been deeply investigated to clarify the relationship between its microstructure and mechanical properties [4,5,6,7,8,9]
Buchheit et al [15], for example, found that 60% of particles between 500 and 700 nm in size were equilibrium S-phase (Al2 CuMg), while Boag et al [16] found a multitude of phases of different chemistry, including S and Metals 2018, 8, 930; doi:10.3390/met8110930
The test duration to reach the minimum creep rate range was estimated on the basis of the results of the constant load experiments (CLE) previously carried out under the corresponding stress
Summary
AA2024 (Al-4%Cu-1.5%Mg) Aluminum alloy is one of the most widely used materials for airplane structures [1,2,3], and, as a result, has been deeply investigated to clarify the relationship between its microstructure and mechanical properties [4,5,6,7,8,9]. At a glance, conclude that this material is fully characterized, many researchers continue to study its high temperature response [10,11,12,13]. The crucial point in further investigating AA2024 is that, differently from its room temperature behavior, a direct correlation between its microstructure evolution during high-temperature exposure and creep response has been seldom achieved. The T3 state consists in solution-treatment, cold working and natural ageing up to a “stable” condition. This combination of heat treatments and cold working is known to produce an extremely complex microstructure. Buchheit et al [15], for example, found that 60% of particles between 500 and 700 nm in size were equilibrium S-phase (Al2 CuMg), while Boag et al [16] found a multitude of phases of different chemistry, including S and Metals 2018, 8, 930; doi:10.3390/met8110930 www.mdpi.com/journal/metals
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