Softening behavior of 8011 alloy produced by accumulative roll bonding process

doi:10.1016/S1359-6462(01)01069-7

Scripta Materialia

Volume 45, Issue 5, 12 September 2001, Pages 597-604

https://doi.org/10.1016/S1359-6462(01)01069-7 Get rights and content

Abstract

Ultra-fine grained Al–Fe–Si 8011 alloy was successfully produced by the accumulative roll bonding (ARB) process. However, softening behavior also happened after 2–3 cycles of ARB. The reason of softening behavior was analyzed preliminarily in this paper.

Introduction

Extensive investigations have demonstrated that a very high plastic strain can produce an ultra-fine grain size in metallic materials. Several techniques are now available for producing the high strains, including cyclic extrusion compression (CEC) [1], torsion straining under high pressure (TS) [2], equal channel angular pressing (ECAP) [3], [4], but one disadvantage of these processes is that they are not applicable to large bulk materials.

One of novel intense straining processes for bulk materials using rolling deformation, named accumulative roll bonding (ARB), was developed recently [5], [6], [7], [8], [9]. In this process, the achieved strain is theoretically unlimited. The ARB process has been successfully applied to aluminum (1100) [5], [6], Al–Mg alloy (5083) [8] and Ti-added interstitial free steel [8], [9]. All these several-cycle ARB processed materials have structures with sub-micron grains and show very high strength at ambient temperature [5], [6], [7], [8], [9].

Commercial 8011 alloy is mainly an Al–Fe–Si alloy, which has a wide variety of end applications owing to the fact that it is possible to control the microstructural evolution of the alloy by means of specific thermal and mechanical treatments [10]. However, in this study we find that the strength at ambient temperature of the ultra-fine grains formed in 8011 alloy by the ARB process did not increase with increasing number of cycles and was lower than that of 1100 alloy in the same processing condition while the solute and particle content in the latter are lower than those in the former [5], [6]. For analyzing the particular softening behavior of 8011 alloy, the changes in mechanical properties and microstructural evaluation during ARB process are presented in this paper. Some complementary experiments on 1100 alloy processed with the same condition as 8011 alloy are also performed for purpose of comparison.

Section snippets

Experimental

The material used in this study was 8011 alloy whose chemical composition is given in Table 1. For comparison, the chemical composition of 1100 alloy is also given. The initial dimension of the materials is 4.0 mm in thickness, and the mean grain size of the 8011 alloy is about 26 μm. For ARB process, the initial materials are cold rolled to the sheets with 1 mm thick (0 cycle, equivalent strain of 1.6).

The repeated cycle of ARB process can be simplified as follows: $Cutting → Surface treatment →$

Mechanical properties

Fig. 1(a) presents the Vickers microhardness of specimens with the plastic strain. It shows that the Vickers microhardness of 8011 alloy produced by ARB increased significantly with strain up to ε=1.6 (0 cycle). Then it kept nearly no change until a strain of 4.0 (3 cycles). After that, it decreased gradually with strain. However, in the same processing condition, the hardness of 1100 alloy increased with strain until strain ε=4.0, and then leveled out.

The ambient tensile properties of the ARB

Discussion

Strengthening in 8011 alloy may be from solid–solution hardening, second-phase precipitation hardening, grain refinement hardening, and/or strain hardening.

Fig. 5 presents the effect of the annealing at 200°C/5 min on the hardness of ARB processed 8011 alloy. It can be seen that the annealing resulted in the decrease of hardness at each cycle in some extent. The ARB process increased the hardness in the first 3 cycles (strain of 4), then had less and less effect on the hardness of the material.

Conclusion

Ultra-fine grained 8011 alloy whose mean grain (or subgrain) size was 800–900 nm was successfully produced by the ARB process. However, softening behavior also happened after 2–3 cycles of ARB. Dynamic recovery and static recovery caused by particles and the decrease of solid solution hardening during ARB process may play the main role on the softening behavior of the 8011 alloy.

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Softening behavior of 8011 alloy produced by accumulative roll bonding process

Abstract

Introduction

Section snippets

Experimental

Mechanical properties

Discussion

Conclusion

Scripta Mater

Mater Sci Eng

Acta Mater

Scripta Mater 39

Acta Mater

Scripta Mater

Aluminium