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Published in:
21-11-2022 | Peer-Reviewed Paper
A Comparative Study on Microstructure and Tribological Properties of Al/Gr Composites Prepared via Conventional and Flake Powder Metallurgy Techniques
Published in: Metallography, Microstructure, and Analysis | Issue 6/2022
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Abstract
Aluminum/graphite composites due to their low density and excellent tribological properties have gained many applications in aerospace and automobile industries. In the present study, for the first time, a relatively new technique termed as flake powder metallurgy (FPM) is utilized for processing of these composites. In the first stage, Al powder particles are mechanically milled in a planetary ball mill up to 9 h. In order to find the optimum milling time and to ensure proper changing of the morphology of powders from near spherical to flake shaped, after each one hour of milling, powder samples were subjected to SEM, sieve analysis and laser particle size analysis. Eventually the optimum milling time obtained as 6 h. The microhardness of powders was quantified at some milling time increments to investigate the effects of the milling time on the extent of work hardening as well as the grain refinement occurred during milling. In the second stage, green compacts of both the as-received and flake-shaped Al Powder particles containing different percentages of flake-shaped Gr particles (0,1.5, 3, 4.5 and 6 volume percent) were prepared by cold pressing. Finally, all the compacts sintered at 650 °C in a tube furnace. Optical microscopy and SEM revealed a uniform distribution of Gr particles within the matrix alloy. The vertical sections of the FPM-processed samples exhibited a layered structure consisting of Al and Gr particles aligned perpendicular to the press direction. The increased Gr content resulted in increased porosity as well as decreased hardness for both the PM- and FPM-processed samples. However, the FPM-processed samples despite of their higher porosity exhibited higher hardness values as compared with their PM counterparts. The results of pin-on-disk wearing tests confirmed superior wear resistance of the FPM-processed Al/Gr composites as compared with their PM counterparts.