A study of the hot working behavior of Al-Mg alloy 5052 by hot torsion testing
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I.
INTRODUCTION
IT is difficult to optimize the commercial hot rolling practice of aluminum alloys for various reasons. First, because commercial-scale ingots often weigh as much as 18,000 kg ( - 4 0 , 0 0 0 lb), it would be extremely expensive to hot work, and possibly scrap, many such ingots over a variety of conditions. In addition, commercial-scale equipment can rarely be freed from production schedules for use in such process development. Consequently, small-scale hot working experiments are often performed to simulate hot rolling in process improvement studies. One such simulation technique is hot torsion testing, 1-6 in which relatively small specimens can be homogenized for a variety of temperatures and times and deformed at temperatures and strain rates (k) corresponding to those used in commercial hot rolling. The torsion machine designed by C. Rossard and coworkers I and manufactured by SETARAM, Lyons, France, is the most sophisticated such machine commercially available. In previous work at our laboratory, we added computer control to the machine, as described elsewhere. 7 The machine is used to generate equivalent tensile flow-stress (~r0) data, which are a measure of the material's resistance to deformation, and equivalent tensile strain-to-failure (el) data, which are a measure of the material's ductility.* In the present study, this hot torsion *Shear stress and strata are converted to eqmvalent tensde stress and strain, respectwely, using the Von Mises criterion.
machine was used to improve the hot rolling practice for A1-2.5 wt pct Mg commercial alloy, 5052. Alloy 5052 is not particularly susceptible to edge cracking, as are higher Mg-containing alloys such as 5182 and 5456. Nevertheless, small edge cracks up to several centimeters long form on the hotline, requiring costly trimming operations and resultant loss of material as scrap. Consequently, cost savings would be realized if the extent of this edge cracking were reduced. Production costs could also be reduced by rolling alloy 5052 under conditions that shorten its homogenization time or reduce its time on the hot line. Rolling at temperatures where the flow stress is lower enables greater reductions, W. PRECHT, Staff Engineer, and J. R. PICKENS, Senior Scientist and Group Leader, Advanced Alloys Group, are with Martin Marietta Laboratories, 1450 South Rolling Road, Baltimore, MD 21227. Manuscript submitted January 23, 1986. METALLURGICAL TRANSACTIONS A
and consequently, fewer passes. In addition, homogenizing the ingots under temperature/time conditions that reduce flow stress and/or increase hot ductility could also improve productivity. The objective of this research is to simulate commercial hot rolling of 5052 by hot torsion testing, and, thereby: 1. Develop a homogenization practice (temperature and time) and identify a deformation temperature range that provides an attractive combination of low flow stress and high hot ductility. 2. Relate observed changes in homogenization and deformation behavior to microstructural changes. 3. As
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