Influence of selective heating on strain-based formability and pore closure rate of sintered powder metallurgy preforms during upsetting

Abstract

An investigation on strain-based formability and pore closure rate of selectively heated sintered powder metallurgical aluminum–titanium composites has been carried out to evaluate the role of heating on the curing of stresses accumulated during mechanical working. Samples with an initial relative density of 90% and an aspect ratio of 1 were prepared through the powder metallurgy technique by applying suitable powder compaction pressures with different titanium contents such as 2%, 4% and 6%. A series of upsetting tests have been carried out on the prepared porous specimens using a 0.5 MN capacity hydraulic press and the failure zone was identified through the experimental work. It was found that failure occurs in the equatorial region of the workpiece due to the accumulation of stresses and the presence of higher amounts of pores. The magnitude of these accumulated stresses and the level of pores affect the formability of the components during cold upsetting. Therefore, there is a need to relieve the accumulated stresses and reduce the pores at the failure zone of the metals. Hence, this work is aimed at relieving the accumulated stresses, reducing the porosity amounts by adopting a novel mechanism of heating in the equatorial region of the samples for various temperatures such as 100 °C, 140 °C, 195 °C, 220 °C and 250 °C. As a result, the forming limit and pore closing rate were found to improve by selectively heating the specimens at locations where stresses have accumulated. Selectively heating this location relieves the accumulated stresses and decreases the number of pores present in the preforms, thereby enabling the metal to reach still higher strain levels before the onset of failure.