Elsevier

Materials Science and Engineering: A

Volume 535, 15 February 2012, Pages 252-257
Materials Science and Engineering: A

The flow behavior modeling of cast A356 aluminum alloy at elevated temperatures considering the effect of strain

https://doi.org/10.1016/j.msea.2011.12.076Get rights and content

Abstract

The flow stress behavior of cast A356 aluminum alloy has been studied by a set of isothermal hot compression tests. The compression tests were carried out in the temperature range of 400–540 °C and strain rates of 0.001, 0.01 and 0.1 s−1 up to a true strain of 0.6. The effects of temperature and strain rate on deformation behavior were represented by Zener–Hollomon parameter in an exponent type equation. Employing an Arrhenius-type constitutive equation, the influence of strain has been incorporated by considering the related materials’ constants as functions of strain. The accuracy of the developed constitutive equations has been evaluated using standard statistical parameters such as correlation coefficient and average absolute relative error. The results indicate that the strain-dependent constitutive equation can lead to a good agreement between the calculated and measured flow stresses in the relevant temperature range.

Highlights

► Flow stress is substantially sensitive to deformation strain rate and temperature. ► Employing an Arrhenius-type equation for describing high temperature flow behavior. ► Material constants, A and Q in the constitutive equations are functions of strain. ► High reliability of the proposed strain-dependent constitutive equations.

Introduction

The workability of cast Al–Si alloys is greatly influenced by the morphology and distribution of the eutectic Si fibers as well as primary aluminum dendrites [1], [2]. Conventionally, the chemical modification and thermal treatment have been employed to refine the microstructure of these alloys [3], [4], [5], [6], [7]. However, this kind of modification is probably accompanied with some shortcomings such as higher density of porosity in the cast structure, long holding times to dissolve the eutectic modifiers and environmental safety concerns [3], [8]. Long time heat treatment at high temperatures may also increase the material's costs. Thermomechanical processing (TMP) is considered as a more effective microstructural modification method controlling the shape and morphology of Si fibers thereby providing superior mechanical properties [9], [10], [11], [12], [13].

To analyze the thermomechanical processes, it is necessary to describe the change in mechanical response under an external loading. This should be conducted in terms of a constitutive equation which relates stress and strain to the related conditions of temperature and strain rate. The latter plays a crucial role in numerical analysis, modeling and finding out the optimum hot forming process parameters. In this regard, various analytical, phenomenological and empirical models have been developed to predict constitutive behavior of a wide range of metals and alloys [14]. Jonas et al. [15] has proposed a phenomenological approach where the flow stress is expressed by the hyperbolic laws in an Arrhenius type of equation. Many researchers have been devoted to assess this equation to suitably applying it to a range of materials [14], [16]. However, most of the previous researches have not generally considered the effect of strain, which possesses a critical effect on the accurate prediction of the respected flow behavior. Taking the effect of strain into account, a revised hyperbolic sine constitutive equation has been recently proposed to predict the elevated temperature flow behavior in 42CrMo steel [17], Ti-modified austenitic stainless steel [18], 9Cr–1Mo (P91) steel [19], pure titanium [20], 2124-T851 aluminum [21], and H62 brass [22].

In recent years many attempts have also been carried out to define a proper relationship describing the instantaneous material behavior in response to strain hardening and dynamic softening mechanisms. Based on classical flow stress-dislocation density relation and kinetics of dynamic recrystallization, Lin et al. [23] and Qin et al. [24] have established constitutive equations to predict the flow behavior of 42CrMo steel and ZK60 magnesium alloy, respectively. The proposed model is capable of predicting the flow behavior of materials in different regions of a typical hot compression stress–strain curve (i.e. work hardening, dynamic recovery and dynamic recrystallization). In addition, introducing a new material parameter (L) which is sensitive to the deformation temperature and strain rate, a new constitutive model has been developed to predict stress–strain curves up to the peak stress in [25].

In the case of aluminum and its alloys, many researchers have studied the high temperature flow behavior using constitutive analysis, a comprehensive review of which would be found in [16]. However, the hot compression deformation behavior of cast aluminum alloys needs to be further investigated to realize the effect of strain. Accordingly, the present work has focused on the relationship between the flow stress, strain, strain rate and temperature to predict the flow behavior of A356 alloy, as the most common cast aluminum alloy. Toward this end, isothermal hot compression tests were conducted in a wide range of strain rates and temperatures. The experimental stress–strain data have been then employed to derive constitutive equation relating flow stress, strain rate and temperature considering the proper compensation of strain. Finally, the validity of the developed constitutive equation has been examined for the entire experimental range.

Section snippets

Materials and methods

The as-cast A356 aluminum alloy was chosen as experimental material the chemical composition (wt%) of which is given in Table 1. The compression testing was conducted according to ASTM E209 standard [26] using cylindrical specimens with 12 mm in height and 8 mm in diameter. The isothermal hot compression tests were carried out at temperatures of 400, 450, 500, 540 °C and strain rates of 0.001, 0.01 and 0.1 s−1 to study the flow behavior of the experimental alloy. The specimens were first preheated

Flow stress characteristics

The experimental true stress–true strain curves resulting from the hot compression tests at different temperatures and strain rates are presented in Fig. 1. As is seen, at temperatures of 400 and 450 °C the flow stress initially increases with strain up to a peak and then decreases by a rate that decays with increasing strain. This softening behavior is likely attributed to dynamic recrystallization (DRX) phenomenon [27] and/or dynamic coarsening and morphological changes of Mg/Si precipitates

Conclusion

In this study, the constitutive analysis of a cast A356 alloy has been carried out performing a set of predetermined hot compression tests. The true stress–true strain curves have revealed that the flow stress is substantially sensitive to deformation strain rate and temperature. A set of constitutive equations coupling flow stress with strain, strain rate and temperature has been proposed. The material constants, A and Q in the constitutive equations have been found to be the functions of

References (38)

  • P.S. Mohanty et al.

    Acta Mater.

    (1996)
  • J. Wang et al.

    Mater. Sci. Eng. A

    (2002)
  • M. Tiryakioglu

    Mater. Sci. Eng. A

    (2008)
  • M. Haghshenas et al.

    Mater. Sci. Eng. A

    (2008)
  • D. Ke et al.

    Mater. Sci. Eng. A

    (2010)
  • D.G. Mallapur et al.

    Mater. Sci. Eng. A

    (2011)
  • R. Jamaati et al.

    Mater. Sci. Eng. A

    (2011)
  • Y.C. Lin et al.

    Mater. Des.

    (2011)
  • H.J. McQueen et al.

    Mater. Sci. Eng. A

    (2002)
  • Y.C. Lin et al.

    Comput. Mater. Sci.

    (2008)
  • S. Mandal et al.

    Mater. Sci. Eng. A

    (2009)
  • D. Samantaray et al.

    Mater. Des.

    (2010)
  • Z. Zeng et al.

    Mater. Sci. Eng. A

    (2009)
  • Y.C. Lin et al.

    Comput. Mater. Sci.

    (2010)
  • Y.H. Xiao et al.

    Mater. Sci. Eng. A

    (2011)
  • Y.C. Lin et al.

    Mech. Res. Commun.

    (2008)
  • Y.J. Qin et al.

    Mater. Sci. Eng. A

    (2010)
  • Y.C. Lin et al.

    Comput. Mater. Sci.

    (2010)
  • H.J. McQueen

    Mater. Sci. Eng. A

    (2004)
  • Cited by (0)

    View full text