Surface roughening with plastic deformation of sintered metals. (1st Report, Development of free surface roughness in upsetting of sintered aluminium.)

Abstract

Surface roughening phenomena in the upsetting of sintered aluminium powder preforms have been investigated experimentally. The effects of the initial density and crystal grain size of sintered preforms on surface roughness development are mainly examined. An empirical expression of the surface roughness development with equivalent strain is derived. In the expression, the variation of density during the upsetting process is taken into consideration in addition to the grain size of sintered preforms. The roughness on the free surface of sintered preforms increases as the plastic strain and grain size increase. This tendency is similar to the case of conventional pore-free metals. However, unlike the pore-free metals, the rate of increase in surface roughness of the sintered preform varies from strain to strain depending on the density during upsetting. When the relative density of sintered preform increases up to about 0.95, the rate of increase in surface roughness is almost reduced to that of pore-free metals.