Optimizing the Parameters in Heat Treatment for Achieving High Hardness and Efficient Bending

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Mechanics, Materials Science & Engineering, September 2016

ISSN 2412-5954

Optimizing the Parameters in Heat Treatment for Achieving High Hardness and Efficient Bending of Thin BS 2014 Aluminium Alloy Sheets Abirami Priyadarshini B. 1

GTN Engineering India Ltd, Tamil Nadu, India DOI 10.13140/RG.2.2.10632.42242

Keywords: hardness measurement, aluminium alloys, bending, aging.

ABSTRACT. The present work targets in setting a standard heat treatment procedure for obtaining high hardness values of the order of 80 HRB in BS 2014 aluminium alloy sheets of 2mm thick commonly used in aerospace industries. A hardness range of 60HRB to 72HRB is possible in low thickness sheets as stated in the standard BS EN 485-2:2013. Experiments were performed to achieve higher hardness values by controlling the heat treatment temperatures thereby understanding the ageing mechanism of the Al-Cu alloy to a wider extent. The validated process sequence in turn resulted in complications where bending of the sheets resulted in cracking. Further investigation was performed and it was found that the BS 2014 alloy has to be bent within two hours of solution annealing in order to have an efficient bending. The results showed that the natural ageing is so rapid in this alloy, which strengthens the material so quickly by the formation of CuAl2 precipitates, thereby, demanding the bending procedure to be performed before the growth of precipitates becomes dominant.

Introduction. The research and innovation at the aircraft industry focuses on reducing the weight of the aircraft for improving the efficiency, safety and performance. It also demands a positive step in environmental and economic factors thereby resulting in a favorable combination of high corrosion resistance, fatigue resistance, formability and strength coupled with low density[1]. Aluminium is one of the most important materials facing these challenges where it finds a wide variety of applications in the aerospace industry depending on their complexity and performance requirements. With copper as the main alloying element, the 2xxx series of aluminium alloys are of significant interest possessing high strength to density ratio and thereby being used for structural applications in variety of fields such as the aviation and military sectors[2], [3]. Aluminium, being a sheet material, demands a predominant level of bending and forming. Among the 2xxx series, the BS 2024 is the most popular alloy used in the manufacturing of aircraft skins, cowls and structures[4]. Currently, the BS 2014 aluminium alloy is gathering attention due to its ability to achieve higher hardness and therefore it is used mainly for the interface beam assembly in aircraft structures and casings. These applications require a balance to be struck between the higher degree of hardness produced with the ability to bend and form the alloy. Work was performed in identifying the precipitates that are responsible for hardening the 2014 Al alloy where the due to the presence of copper was of significant importance[5]. A good combination of mechanical properties can be achieved by controlling the precipitation mechanism where the elements such as Magnesium and Silicon are also responsible in improving the hardness of this alloy[6]. In the present work, the BS 2014 alloy was targeted to produce an increased hardness by optimizing the heat treatment factors thereby having an efficient control over the ageing mechanism. BS EN 4852:2013 states a maximum hardness of 72 HRB that could be achieved in a 2014 alloy[7]. However, this alloy has been studied widely for its ageing process where the precipitates are solely responsible in hardening the alloy resulting from the copper addition[2], [5]. Sadeler et al. studied the effect of T4 (solution treated and naturally aged) and T6 (solution treated and artificially aged) tempers where they concluded that the T6 temper has positive effects on the mechanical properties of this alloy[8]. MMSE Journal. Open Access www.mmse.xyz

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