Strengthening of Al through addition of Fe and by processing with high-pressure torsion
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NANOSTRUCTURED MATERIALS
Strengthening of Al through addition of Fe and by processing with high-pressure torsion Jorge M. Cubero-Sesin • Zenji Horita
Received: 16 August 2012 / Accepted: 3 October 2012 / Published online: 10 October 2012 Ó Springer Science+Business Media New York 2012
Abstract Iron is a common impurity element in aluminum and is expected to be used in a controlled manner. In this study, high-pressure torsion (HPT) was applied to 10-mm diameter bulk disk-type samples of Al–Fe alloys with different Fe additions: 2 and 4 wt%, and different initial states: as-cast, extruded, and annealed. Intense strain was introduced to the materials by HPT processing at room temperature under a pressure of 6 GPa for up to 75 revolutions. Tensile tests showed that a significant increase in the UTS above 500 MPa occurs with 13 % elongation in the Al–2 % Fe sample processed by HPT from the as-cast state. Microstructural analyses revealed that a close-to nanograined microstructure with a size of 125 nm and dispersion of intermetallic particles below 50 nm was attained, along with a maximum supersaturation of Fe of *0.67 wt%. The Al–4 % Fe sample reached even higher supersaturation of Fe to *0.99 % and similar strength but lower elongation due to insufficient fragmentation of coarse intermetallics. It is concluded that the eutectic structures in the cast state are a major contributor to the enhanced strengthening and the retained elongation. The saturated states of the microhardness at equal Fe contents were shown to be similar regardless of the initial state upon sufficient straining by HPT.
J. M. Cubero-Sesin (&) Z. Horita Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan e-mail: [email protected] J. M. Cubero-Sesin Z. Horita International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 819-0395, Japan
Introduction High-pressure torsion (HPT) has been proven to be an efficient processing technique to refine the microstructures of metals and alloys to ultrafine and even to nanocrystalline levels, thus developing very interesting and novel properties in contrast with the ones achievable by traditional processing methods [1–3]. The use of Fe as an alloying element in Al presents a good example of this situation. In the Al-rich side, there is very limited equilibrium solid solubility of Fe in Al, which is almost none at room temperature. Thus, there is presence of hard intermetallic phases at very low fractions of Fe, often in the form of eutectics over a wide range of cooling rates [4, 5]. This presents large potential for enhanced strength and resistance to high-temperature deformation. However, the brittle nature of intermetallics reduces the formability of Al–Fe alloys, especially when coarse phases form at hypereutectic compositions. Hence, the Fe additions are kept low when compared to other alloying elements [4, 6]. So, it becomes interesting if the Fe content, as a leftover from industrial
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