45 Degree Equal Channels Angular Pressing for Grains Refinement and Softening of Lead Alloy

Abstract

Severe plastic deformation (SPD) has over the times been employed in the production of enhanced lightweight metals and generally to improve a specific property of material without introducing expensive alloying elements to the current materials or applying high energy demanding heat treatment technique. This paper examined the influence of severe plastic deformation of lead alloy using equal channel angular pressing (ECAP). The technique was applied to lead alloy at room temperature using channel angles of 45°. The materials were processed up to three ECAP passes and subjected to equivalent strains of 8.70. Hardness test, impact test, and microstructural changes of the processed materials were examined. Results showed that extrusion force reduced as the strain level increased and that dynamic recrystallization and structural changes reduced the hardness of lead processed through 45^o ECAP. Hardness of 8.95 HV was recorded when the material was processed through third ECAP pass, while 9.05 HV was recorded for second ECAP pass. The analysis shows clear reduction in the material hardness as number of pass increases when compared to the control sample with hardness of 16.77 HV. The result of impact test showed no clear difference between the values obtained for the material when processed through second and third pass because the amount of energy absorbed remained unchanged from 4 J for the two passes. Analysis of microstructure images also revealed that increasing the strain level leads to break down and dissolution of antimony rich precipitate. The microstructural change caused by ECAP of the control sample softens the material, as a result of break-up of the original precipitate structure and the acceleration of the dynamic recrystallization of the material.