Development of a submicrometer-grained microstructure in aluminum 6061 using equal channel angular extrusion
- PDF / 491,001 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 178 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Development of a submicrometer-grained microstructure in aluminum 6061 using equal channel angular extrusion Stephane Ferrasse,a) Vladimir M. Segal,b) K. Theodore Hartwig, and Ramon E. Goforth Mechanical Engineering Department, Texas A&M University, College Station, Texas 77843-3123 (Received 7 August 1995; accepted 24 October 1996)
Submicrometer-grained (SMG) microstructures are produced in an Al –Mg–Si alloy (6061) by subjecting peak-aged and overaged billets of the alloy to intense plastic strain by a process known as equal channel angular extrusion. Two types of refined structure are distinguished by optical and transmission electron microscopy. One structure is created through intense deformation (four extrusion passes through a 90± die, e 4.62) by dynamic rotational recrystallization and is a well-formed grain (fragmented) structure with a mean fragment or grain size of 0.2 –0.4 mm. The other structure is produced by post-extrusion annealing through static migration recrystallization, resulting in a grain size of 5–15 mm. Intense deformation of peak-aged material to a true strain e of 4.62 (four passes) produces a strong, ductile, uniform, fine, and high angle grain boundary microstructure with increased stability against static recrystallization as compared to the overaged material.
I. INTRODUCTION
Recent work shows that severe plastic deformation promotes grain refinement and appears to be an effective way to form submicrometer-grained (SMG) materials.1–3 The fine grains are beneficial from the standpoint of increased strength, toughness, and fatigue life. The finer grains also promote superplasticity at lower temperatures and faster strain rates. The production of a superfine structure using conventional metalworking methods is often difficult, especially for massive or bulk products. This is true, for example, when thermomechanical treatments involving static or dynamic recrystallization are used to enhance grain refinement in aluminum alloy.4–6 Traditional techniques for introducing high levels of deformation such as forging, extrusion, drawing, or rolling impose significant limitations on required equipment and product characteristics; high forces and pressures are needed, work piece sizes are restricted, changes in work piece dimensions occur and high levels of strain nonuniformity often result. Many of these limitations are overcome by a material processing innovation called equal channel angular extrusion (ECAE), which offers many technological advantages for grain refinement.7–10 The benefits of ECAE come from its ability to produce intense deformation by simple shear through innovative die design. Contrary to conventional extrusion, the crosssectional area of billets or ingots extruded via ECAE is not reduced. The process can therefore be applied
a)
Current address: Sollac Dunkerque, CRDM, Dunkerque, France. Current address: Principal Research Scientist, Johnson Matthey Electronics, Spokane, Washington 99216.
b)
J. Mater. Res., Vol. 12, No. 5, M
Data Loading...
