Deformation characteristics of aluminium-copper composite preforms at different strain rates during cold forging

摘要

The paper presents an investigation into the deformation characteristics of aluminium-copper composite preforms at different strain rates (based on ram velocity) during cold forging under lubricated end conditions. The preforms were prepared and forged at different ram velocities: 1.5, 50, 100 and 150 mm/min. The forgeability of all the composite preforms was noted when cracks were observed on the equatorial free surfaces at corresponding percent reduction in height. The yield criterion as proposed by Tabata and Masaki, composite friction law, an appropriate velocity field, a mathematical model considering 'upper bound' analysis was developed for relative average forging pressure on the platen during cold forging of the composite preform at different ram velocities. Theoretical results have been presented graphically showing the variation of the relative average forging pressure versus percent reduction in height of these composite preforms. Experimentally obtained forgeability of different composite preforms at different ram velocities have been plotted with respect to: 1) percent reduction in height; 2) forging stress; 3) compressive strength; 4) percent increase in bulge diameter; 5) linear hoop strain. Theoretical and experimentally obtained values of relative average forging pressure versus percent reduction in height of the preform were plotted for different composite-preforms and a good correlation was observed.