Abstract
Upsetting tests of sintered aluminum powder preforms with different initial relative densities are carried out at various temperatures and strain rates to examine the effects of these factors on the flow stress and the density change. A computer controlled high speed press is used to keep a constant strain rate throughout an upsetting process, and lubrication is repeated at every 0.1 axial strain to avoid both the friction between tools and specimen and the temperature rise due to plastic deformation. The effects of temperature and strain rate on the material constants N, a and b which are included in the Oyane and Shima plasticity theory of porous materials are also discussed. The flow stress in the practical forming condition in which the temperature of specimen increases with increasing strain is considered based on the stressstrain curves at a constant temperature. Experimental results show that the density change of sintered material hardly depends on the temperature and strain rate, but that the flow stress increases with increasing strain rate and decreases with increasing temperature.
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