Homogenisation Efficiency Assessed with Microstructure Analysis and Hardness Measurements in the EN AW 2011 Aluminium Alloy

Maja Vončina,Borut Žužek,Tilen Balaško,Irena Paulin,Aleš Nagode,Jožef Medved

doi:10.3390/met11081211

Maja Vončina, Borut Žužek + Show 4 more

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https://doi.org/10.3390/met11081211

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Abstract

When extruding the casted rods from EN AW 2011 aluminium alloys, not only their homogenized structure, but also their extrudable properties were significantly influenced by the hardness of the alloy. In this study, the object of investigations was the EN AW 2011 aluminium alloy, and the effect of homogenisation time on hardness was investigated. First, homogenisation was carried out at 520 °C for different times, imitating industrial conditions. After homogenisation, the samples were analysed by hardness measurements and further characterised by microscopy and image analysis to verify the influence of homogenisation on the resulting microstructural constituents. In addition, non-equilibrium solidification was simulated using the program Thermo-Calc and phase formation during solidification was investigated. The homogenisation process enabled more rounded shape of the Al2Cu eutectic phase, equilibrium formation of the phases, and the precipitation in the matrix, leading to a significant increase in the hardness of the EN AW 2011 aluminium alloy. The experimental data revealed a suitable homogenisation time of 4–6 h at a temperature of 520 °C, enabling optimal extrusion properties.

Highlights

Al-Cu based 2xxx alloys offer high strength with low specific weight and are widely used in the form of extrusions for major structural components, in the aircraft industry
The results show that the temperature range for the dissolution is 450–540 ◦ C
2 indicating solidus temperature occur as◦Cu-based eutectic starts to melt

Summary

Introduction

Al-Cu based 2xxx alloys offer high strength with low specific weight and are widely used in the form of extrusions for major structural components, in the aircraft industry. These alloys exhibit low extrusion rates, require high extrusion pressure, and are assigned a low extrudability index [1,2]. Non-equilibrium solidification usually results in micro-sized eutectic phases with a relatively low melting point [3,4,5] that are likely to melt and cause irreversible damage during thermomechanical treatments at high temperatures [6]. Cast ingots must undergo a homogenisation treatment before extrusion to eliminate micro-segregation, modify the intermetallic phase type, and morphology to improve extrudability [6,10]. Precipitation is controlled in this way [4]

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