Phenomenon of strain hardening behaviour of sintered aluminium preforms during cold axial forming

Cold upsetting experiments were carried out on sintered aluminium preforms in order to evaluate their work-hardening characteristics. Aluminium powder preforms of 92% of theoretical density, with three initial aspect ratios were prepared using a suitable die-set assembly on a 1.0 MN capacity hydraulic testing machine. Sintering was carried out in an electric muffle furnace for a period of 1 hour at 520 °C. Each sintered compact was subjected to incremental compressive loading after each step of deformation. The instantaneous strain hardening exponent ni and strength coefficient ki of the aluminium preforms were calculated and found to be reached the peak value when the deformation or packing density is at low value. Further, it has been observed that the value of ni and ki decreased and found to be constant for both of the aspect ratios of the preforms tested. It has further been established that the initial geometry of the P/M preforms played a predominant role in influencing both ni and ki.