The effects of room temperature ECAP and subsequent aging on mechanical properties of 2024 Al alloy

doi:10.1016/j.jallcom.2013.09.202

Journal of Alloys and Compounds

Volume 585, 5 February 2014, Pages 753-759

https://doi.org/10.1016/j.jallcom.2013.09.202 Get rights and content

Highlights

•
Many of the short shear bands were observed on the microstructure after one pass of cold ECAP.
•
The dislocation density and coherent domain size of studied alloys were determined by XRD analysis.
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Significant increases in hardness and yield strength were obtained after one pass of cold ECAP.
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Aging of deformed sample at 100 °C was better than 70 °C to improve the hardness and the yield stress.

Abstract

Mechanical properties of the 2024 aluminum alloy, which was plastically deformed by equal channel angular pressing (ECAP) at room temperature and aged naturally and artificially at 70 °C and 100 °C for different times, were investigated in this research. Many of the short shear bands were observed on the microstructure after one pass of ECAP and led to fragmentation of grains. Hardness and yield stress of the sample aged naturally after deformation were considerably improved due to increase of dislocation density calculated by XRD data analysis and their interaction with solute atoms during ECAP. The ductility and work hardening exponent of the deformed samples were significantly reduced due to formation of shear bands within the microstructure. However aging the samples immediately after sever plastic deformation at 70 °C and 100 °C caused an additional improvement in hardness and yield stress relative to the samples aged naturally after deformation.

Introduction

Mechanical properties of metal alloys can be improved by forming processes such as ECAP [1], [2]. This process presented by Segal et al. [3] at 1977 has been widely used by many researchers since then [4], [5]. Mechanical properties of most age-hardenable aluminum alloys can be improved by this method. It is well known that the most part of improvement in mechanical properties of the fully annealed aluminum alloys is achieved in the first pass of ECAP process [4], [6]. For example according to Horita et al. [6] fully annealed Al alloys such as 1100, 6061 and 7075 can obtain 80–90% of their maximum values of their yield stress only after one pass ECAP. Also some reports indicate that a significant improvement in mechanical properties of age hardenable aluminum alloys in solution annealing condition, can be achieved via one pass of warm ECAP and subsequent aging at low temperatures [6], [7], [8]. For example according to Kim et al. [8], the yield stress of 2024 aluminum alloy can be improved by 110%, i.e. from 320 MPa to 628 MPa after one pass of warm ECAP and subsequent aging at 100 °C for 20–30 h.

It has been reported [8], [9] that increase in the dislocation density during ECAP not only improves material strengthening, but also it can increase the rate of precipitation during aging. So that formation of fine precipitates and further improvement in mechanical properties can be expected. However, dynamic recovery in warm ECAP of age hardenable Al alloys can cause a decrease in dislocation density of the deformed material and consequently dislocation strengthening is decreased [10], [11]; one should consider cold ECAP as a substitute for deformation of these material. Recently some published reports show that improvement in mechanical properties can be achieved by one pass of cold ECAP in age hardenable aluminum alloy [12], [13], [14] due to elimination of dynamic recovery in this process which cause saturation in subgrain dislocation density, hence optimum mechanical properties are achieved [15]. Moreover from economic point of view, according to Bidulsky [16], using one pass of cold ECAP is beneficial for making aluminum PM parts, as application of this process can control the porosity content.

Deformation of aluminum alloys EN AW 2014 by one pass of cold ECAP after solution annealing and water quenching, resulted to improvement of its yield stress from 157 MPa to 511 MPa due to grain refinement and strain hardening of solid solution according to Kvackaj et al. [12], [13]. However, subsequent artificial aging at 100 °C did not considerably affect YS & UTS of the ECAPed alloy. In another study, Danaf [14] reported that the usage of one pass of cold ECAP for commercial Al alloys 1050, 5083, 6082 and 7010 result to domination of low angle grain boundaries within the microstructure of ECAPed alloys. The amount of decrease in grain size in his study was considerable especially in age hardenable alloys 6082 and 7010. In addition hardness and yield strength of the ECAPed alloys were sharply increased due to grain refinement and dislocation strengthening during cold ECAP.

The above mentioned reports basically related to the cold ECAP of some Al alloys at room temperature, does not include 2024 Al alloys which is a high strength age hardenable alloy. About formability, variation of mechanical properties and structural parameters like dislocation density of this alloy by cold ECAP there is no published information. Thus the aim of this study is to investigate the mechanical properties and structural parameter include crystallite domain size, lattice microstrain and dislocation cell size of 2024 Al alloy.

Section snippets

Experimental procedure

Commercial aluminum alloy 2024-T8 in the form of extruded rod of 20 mm in diameter with mean chemical composition of Al–4.2Cu–1.26 Mg–0.63Mn–0.42Fe–0.29Si (in wt.%), was used in this research. Cylindrical specimens with a diameter of 11.7 mm and length of 70 mm were made via machining. They were solution annealed at 500 °C for 40 min and quenched in water prior to their deformation. Quenched samples were immediately subjected to severe plastically deformation at room temperature using ECAP die. The

Microstructure

The microstructure of the polished specimen of the as-received material after solution annealing is shown in Fig. 2. This microstructure shows there are three types of intermetallic compounds (coded P₁, P₂ and P₃) within the microstructures; the round particles are rich in Al, Cu and Mg, the larger particles having angular shapes are rich in Al, Cu, Fe and Mn and the rod shape particles are rich in Al, Si, Fe, and Mn on the base of the results obtained by EDAX analysis. These results are

Conclusions

1.
Severe plastic deformation of 2024 aluminum alloy with one pass of ECAP at room temperature generated copper-type or short shear bands within the microstructure.
2.
The result of X-ray diffraction analysis showed that the dislocation density of the solution annealed sample considerably increased and dislocation spacing decreased after one pass of cold ECAP processing.
3.
Significant increases in hardness and yield strength of the deformed and aged material can be attributed to increase in dislocation

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The effects of room temperature ECAP and subsequent aging on mechanical properties of 2024 Al alloy

Highlights

Abstract

Introduction

Section snippets

Experimental procedure

Microstructure

Conclusions

Progress in Materials Science

Progress in Materials Science

Materials Science and Engineering: A

Materials Science and Engineering: A

Journal of Materials Processing Technology

Scripta Materialia

Acta Materialia

Materials Science and Engineering: A

Journal of Alloys and Compounds

Materials & Design

Materials Science and Engineering: A

Scripta Materialia

Materials Science and Engineering: A

Acta Metallurgica

Acta Materialia

Materials Science & Engineering

Materials Chemistry and Physics

Acta Materialia

Materials Science and Engineering: A

Materials Science and Engineering: A