An experimental investigation on strain hardening behaviour of aluminium – 3.5% alumina powder metallurgy composite preform under various stress states during cold upset forming

An experimental investigation on instantaneous strain hardening behaviour of aluminium – 3.5% alumina powder metallurgy composite preforms for three different stress state conditions, namely, the uniaxial, the plane and the triaxial has been carried out. Sintered aluminium–alumina composite with three different aspect ratios (height to diameter ratio), namely, 0.35, 0.56 and 0.72 and two different initial preform relative densities of 0.80 and 0.90 were prepared, sintered at 550 ± 10 °C under the cover of protective indigenously developed ceramic coating for a period of 90 min in an electric muffle furnace and cooled inside the furnace itself. Sintered but mildly machined disc specimens were cold deformed under axial tests using mirror polished flat dies. The instantaneous strain hardening exponent (ni) and the instantaneous strength coefficient (Ki) were determined for each aspect ratios for all three different stress state conditions and the results were analyzed in the present work. The analysis of the experimental results has shown that the instantaneous strain hardening exponent (ni) and the strength coefficient (Ki) are greater for the triaxial stress state condition irrespective of the initial preform densities and the aspect ratios when compared to uniaxial and plane stress state conditions.