Large wire drawing plastic deformation in aluminum and its dilute alloys

Abstract

The microstructures and hardening characteristics of Al and Al with dilute additions of soluble and insoluble impurities were compared during wire drawing at room temperature to true strains (e w ) of 4.95. Three stages of microstructure change are observed: formation of a dislocation cell structure; cell boundary sharpening and cell size refinement; dynamic recrystallization. A minimum effective cell size is reached at an intermediate strain level corresponding approximately to the onset of dynamic recrystallization. The amounts and types of impurities at levels less than 1 pct have a great effect on the details of the microstructural changes as well as the hardening characteristics. 99.98 pct pure Al alternately saturates and hardens frome w = 0 to 4.95. Al-0.6 Fe (insoluble) work softens neare w = 3.5. Al-0.2 Mg (soluble) and EC Al (with 0.15 pct soluble and insoluble impurities) both work harden at a diminishing rate toe w ≃1.25 then enter a linear hardening stage which persists toe w ≃5. A linear relation between yield strength and inverse cell size is established for EC Al and Al-0.2 Mg in the cell refinement strain range; however, the Petch slope is much less than that of similar Al alloys subjected to elevated temperature dynamic or static recovery. Al-0.6 Fe does not exhibit a consistent linear relation between yield strength and inverse cell size. These differences can be attributed to the degree of recovery and the interrelation between cell size, cell boundary character and total dislocation density.