The effect of heat treatment on hot deformation behaviour of Al 2024

doi:10.1016/j.jmatprotec.2007.11.261

Journal of Materials Processing Technology

Volume 206, Issues 1–3, 12 September 2008, Pages 25-29

https://doi.org/10.1016/j.jmatprotec.2007.11.261 Get rights and content

Abstract

In this study, hot deformation behaviour of 2024 Al alloy has been investigated using hot pressure test up to 400 °C temperature range with strain rates of 0.001–0.1 s⁻¹. The results show that increasing strain rate, leads to an increase in flow stress. In solid solution state in low temperatures, dynamic precipitation happens during deformation and particles grow dynamically. Dynamic work softening occurs during hot deformation and decreases the stress. In deformation of the samples in annealed state in low temperature no stress loss has been observed during hot deformation. This difference in hot deformation of the samples has been related to precipitation characteristics.

Introduction

The most important mechanism for restoration during hot deformation of aluminium alloy is dynamic recovery (DRV) (McQueen and Blum, 2000, McQueen, 1991a). In fact, dynamic recovery is the recovery of some mechanical properties of the deformed metal, and become more similar to the undeformed condition. This process usually happens at temperatures in which dislocations have enough mobility and the rate of dislocation removal is equal to their production. In addition, kinetic of recovery depends on the properties of secondary phase particles such as size and distance between them (McQueen, 1991b, Paillard and Humphreys, 1996). Since heat treating before hot deformation affects the properties of secondary phase particles, recovery kinetics and also static and dynamic growth during deformation or just after that, will be affected. Consequently, the amount of work softening and workability will change with heat treatment before deformation (Kassner et al., 1993).

The studies carried out on the effect of secondary phase on recovery behaviour, formability and microstructural changes in Al alloys show that precipitation process at high temperatures (>400 °C) will increase workability. In addition, at high temperatures, the amount of solute elements in the matrix increases and leads to an increase in flow stress during hot deformation (McQueen and Lee, 2000, Spigarelli et al., 2000, Verlinden et al., 1990). But there are few works performed on the effects of secondary phase in temperature range of 350 °C, 400 °C and the effect of heat treatment before deformation in the mentioned temperature range.

In this study, Al 2024 alloy is homogenizing to investigate the effect of heat treatment on its hot working behaviour, different thermomechanical cycles were planned and performed, and the achieved results were studied.

Section snippets

Experimental procedure

The chemical composition of Al 2024 used in this study has been shown in Table 1. The initial microstructure was composed of dendrite lamellas lying parallel to the billet axis, as shown in Fig. 1.

The cylindrical samples were machined parallel to the ingot axis into rods with a diameter of 10 mm and a length of 15 mm. The first group of samples was homogenized and solution treated at 500 °C for 16 h (T₁), as shown in Fig. 2. The microstructure of first group is shown in Fig. 3. So keeping the

Results and discussion

True stress–true strain diagrams after hot compressing test with different strain rates on T₁ samples have been shown in Fig. 4. As can be observed, in the true stress–true strain curve at 350 °C, an increase in the strain will lead to increasing in flow stress, and flow stress decreases after reaching a maximum. In addition, increase in temperature and decrease in strain rate will reduce the amount of flow stress. In order to quantitatively study the amount of work softening, relative softening

Conclusion

The main points resulted from the present work are as follows:

1.
In the samples, which are preheated at 400 °C, nucleation happens before the beginning of deformation. This will lead to significant decrease in the amount of work softening comparing deformation at 350 °C, due to the greater size of the precipitates.
2.
Hot deformation behaviour of T₂ samples at 350 °C is completely different from those of supersaturated (T₁) samples which were hot deformed at similar temperature.
3.
The reduction of stress in

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The effect of heat treatment on hot deformation behaviour of Al 2024

Abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusion

Mater. Sci. Eng. A

Acta Mater.

Mater. Sci. Eng. A

Mater. Sci. Eng. A

Mat. Sci. Eng. A

Hot workability of some heat treatable aluminium alloys