Institute of Fundamental Technological Research

In the metal forming process, the understanding of metal flows and the fracture strains are most significant to the failure/damage of the components. Usually, in metalworking, damage occurs because of nucleation, growth and coalescence of the void into a small fracture. These small fractures increased in the circumferential path due to the existence of stresses and the pores which leads to failure at the equatorial position during the upsetting of porous samples. Hence, the fracture of the workpieces strongly depends on the stresses and the pores. Such form of stresses and pores if relieved will give a better damage limit of the material. Therefore, in this research, a novel scheme of localised heating is adopted at the equatorial position of the compressed samples to enhance the critical damage parameter. The powder metallurgy route was used to prepare the required compacts with different relative densities (80%–90%) and 1 aspect ratio by applying suitable powder forming pressures. The upsetting test was performed on the obtained porous samples for various weight percentages of titanium (2%–6%) in the aluminium at the stable strain rate (0.1 s^−1) and the damage location was noticed for various components. After the identification of damage position, various temperatures (100 °C–250 °C) of localised heating were attempted on the failure site of the specimens after some incremental stages of upsetting tests. The experimental results were analysed using various damage criteria and it was found that the initiation of failure is delayed and increased the critical damage value by selectively heating the samples because of relieving the stresses, reduction in porosity and changes in microstructure.

aluminium, failure parameter, localised heating, powder metallurgy, strain path, titanium, upsetting

In the present work, localised heating has been adopted at the damage site of the cold upset materials and the role of this mechanism on the workability has been analysed. Cylindrical specimens containing 96% aluminium and 4% titanium were prepared through powder metallurgy technique with an aspect ratio (height to diameter) of 1 by suitable pressures. A series of cold upsetting test was conducted and the material properties for various preforms initial relative densities (80%, 85% and 90%) were determined under the stable strain rate. The flow of metals was analysed using a finite element tool and it was observed that the metal flow starts from near the centre zone to the equatorial zone and the damage happens in the outer position because of more amount of accumulated stresses and the pores. These stresses and pores decrease the workability of the final component. Hence, the present research is intended to reduce the stresses and minimize the pores by applying a localized heating (100 °C–250 °C) at the equatorial sites of the components and thereby increasing the workability of the material. Also, heating selectively at the equatorial site of the workpiece improves the workability due to change in grain size and it was noticed that the grain size of the developed porous preforms was high for the higher heating conditions due to the growth of the grains. Therefore, the localized heating adopted in this work is a superior method to enhance the workability of the powder samples and this novel technique could be useful in improving the workability of the structural components that have extensive applications in the automobile and aerospace industries.

powder metallurgy, workability, localised heating, aluminium, titanium, upsetting