A comparison of continuous SPD processes for improving the mechanical properties of aluminum alloy 6111
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L.S. To´th Laboratoire de Physique et Me´canique des Mate´riaux, Universite´ Paul Verlaine de Metz, Ile du Saulcy, 57045 Metz, France
M. Winkler CoE Design in Light Metals, Department of Materials Engineering, Monash University, Melbourne 3800, Australia
S.L. Semiatin Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/RXLM, Wright-Paterson Air Force Base, Ohio 45433-7817 (Received 7 July 2008; accepted 27 October 2008)
Microstructure evolution, mechanical properties, formability, and texture development were determined for AA6111 samples processed by asymmetric rolling (ASR) with different roll friction, velocity, or diameters, conventional rolling (CR), and equalchannel-angular pressing (ECAP). Highly elongated or sheared grain structures were developed during ASR/CR and ECAP, respectively. ASR led to improved r-values and formability compared with CR primarily as a result of the development of moderate shear-texture components analogous to those developed during ECAP of billet material. ASR based on different roll diameters gave the best combination of strength, ductility, and formability.
I. INTRODUCTION
The expanding use of aluminum alloys instead of steels in automotive components is driven by the desire to reduce weight and fuel emissions. For example, the replacement of steel parts with aluminum can reduce the weight by approximately 40–50%.1 However, aluminum alloys are more expensive and have inferior formability compared with steels. Among the many possible aluminum alloys for automotive applications, AA6111 in sheet form has become the most widely used for body panels due to its good corrosion resistance, reasonable formability, and excellent paint bake hardening to a strength level above 300 MPa without the need for a separate age-hardening step.2 Despite significant work in the area of thermomechanical processing, conventional rolling (CR) techniques used to produce AA6111 sheets3 do not yield a competitive material for autobody applications, inasmuch as the resulting formability even after heat treatment is lower than in steel. The optimization of properties in production operations should be done at each stage a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0060 J. Mater. Res., Vol. 24, No. 2, Feb 2009
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before/after cold rolling and during various heat treatments; the total gain in formability benefits from an improvement at each stage of processing as has been shown for AA5005.4,5 Improvements in mechanical properties due to the cold rolling stage can be further enhanced by subsequent heat treatment. A study of different heat treatment schedules after equal-channel-angular pressing (ECAP) of AA6111 sheet was conducted earlier6 and is thus not discussed in the current paper. Limitations in formability due to the rolling texture can be greatly reduced through the use of an additional processing step to develop a shear texture into the sheet product. For th
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