Microstructure and Texture Evolution during Single- and Multiple-Pass Friction Stir Processing of Heat-Treatable Aluminu
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ALUMINUM alloys are widely used in aerospace and ground transport applications due to their high strength-to-weight ratio and good corrosion resistance. Heat-treatable aluminum alloys have the highest specific strength among all the alloys due to the strengthening obtained through precipitation hardening. Highest strength among all the heat-treatable alloys is exhibited by 7XXX (Al-Zn-Mg-Cu) series, and the same is preferred when strength is the overriding criterion.[1] In situations when damage tolerance[2] is a primary requirement, 2XXX series (Al-Cu and Al-Cu-Mg) is
NARESH NADAMMAL and SATISH V. KAILAS are with the Department of Mechanical Engineering, Indian Institute of Science, Bangalore, Karnataka, 560012, India. Contact e-mail: nareshnn@ mecheng.iisc.ernet.in JERZY SZPUNAR is with the Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada. SATYAM SUWAS is with the Department of Materials Engineering, Indian Institute of Science, Bangalore, Karnataka, 560012, India. Manuscript submitted January 9, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
widely used. In the 2XXX series of aluminum alloys, the alloy 2024 and its advanced versions are the most commonly used structural materials for manufacturing critical components such as fuselage skins of aircrafts. The addition of Mg into the Al-Cu system leads to a faster and significantly different precipitation and recrystallization kinetics in the alloy 2024, compared to the conventional Al-Cu alloys.[3] To further enhance the strength of these alloys grain refinement is a possibility. Severe Plastic Deformation (SPD) techniques,[4–7] which are based on the top-down approaches in materials processing technology, offer ample scope for grain refinement, and property enhancement in structural materials. The most significant SPD techniques include equal channel angular processing (ECAP), High-pressure Torsion (HPT) and Accumulative Roll Bonding (ARB).[8–15] FSP was introduced as a SPD technique in the year 2000 by Mishra et al.[16]; FSP technique was derived from the revolutionary solid state joining method of friction stir welding (FSW). With the advantage of using a conventional milling machine for processing, FSP has become one of the most promising methods for bulk materials processing. Unlike the processes that are discontinuous in nature such as
ECAP, FSP is a continuous process where fine-grained microstructures can be produced. Further, fine-grained structures can be generated in a local region or throughout the complete plate. During the process, high temperatures, close to 0.7Tm, get generated, which can lead to a relatively larger grain size. However, with many advantages such as simplicity of the processing, eco-friendliness, and the ease of scaling up for bulk production, this technique unveils a huge potential as an industrial process. Major parameters that control the efficiency of FSP include tool rotational speed, tool traverse speed, tool tilt angle, and tool geometry. For a single-pass FSP, a bottom-up ap
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