High temperature deformation of a commercial aluminum alloy
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INTRODUCTION
HOTforming of metals is common practice in industry due to the high degree of deformation obtainable at low stress without intermediate anneals. The microstructures developed during such processes are unstable at elevated temperatures and promote structural transformations due to static recovery and static recrystallization as well as grain growth. The interaction of static and dynamic structural changes promotes the complete evolution of microstructure and hence the ductility of the material. 1,2.3An important role in determining hot ductility is also given by the interaction between formation and fracture mechanisms. 4'5"6 The main softening processes in hot working (T > 0.5 Tm) that minimize the stored strain energy are dynamic recovery and dynamic recrystallization.7 In dynamic recovery mechanisms the dislocations are rearranged into a substructure consisting of subgrains through the disintegration and reformation of subboundaries at constant spacing, thus maintaining equiaxed subgrain. This process is sometimes called repolygonization and the higher the Stacking Fault Energy (SFE), the more effective it is. 2'8'9 Both dynamic recovery and dynamic recrystallization have been described as two mutually competitive processes. In fact, in polygonization the stored strain energy is minimized, so reducing the driving force for recrystallization in those points where the strain energy produced by deformation is locally high. 5'1~In the interpretation of hot working mechanisms, many authors consider the SFE decisive. In metals with high SFE, such as aluminum, dynamic recovery appears tG be the sole softening mechanism in hot working. H-~5 In metals with low SFE such as copper, dynamic recrystallization is the dominant process. 2,3,16 The alloying in solution aids dynamic recrystallization during hot forming. ~7'~8 Because of the effects of structural changes during hot working on the properties of the final sheet produce, it is important to identify the deformation mechanism, under what circumstances they occur, to what extent and at what stage in the working cycle. The structures formed during working, whether polygonized or recrystallized, depends in general on e, k, T, and o-. The relationship among the various parameters generally depends on the particular mechanism E OLLA, Associate Professor of Metallurgical Process, and P.F. VIRDIS, Professor of Metals Science, are with Institute of Applied Chemistry and Metallurgy, University of Cagliari, Cagliari, Italy. Manuscript submitted October 24, 1985. METALLURGICALTRANSACTIONS A
involved and on the resulting structural evolutions. I1'~9-24 The object of the study was to investigate the hot ductility of a commercial aluminum alloy and to identify the parameters governing the deformation process, since product quality depends to large extent on the ductility of the material.
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EXPERIMENTAL PROCEDURES
For investigation a commercial aluminum alloy with a composition in wt of 0.13 pct Si, 0.7 pct Fe, 0.02 pct Ti, 0.01 pct Cu, 0.02 pct Mn, 0.05 pct Zn, At
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