Abstract
Poor wetting of reinforcement by the matrix has been a major problem associated with the sintering of powder metallurgy products. Metals such as Mg, Sn, and Pb have been used as wetting agents to facilitate the sintering processes. In this work, the effects of compaction pressure, sintering temperature, time, and furnace atmosphere on the exudation of liquids during the sintering of Al-AlN-Mg compacts have been carried out. The powders were shaped using the compaction pressures of 350mpa and 450mpa then sintered at 5500C and 6000C for 30, 60 and 90 minutes in hydrogen and nitrogen atmospheres. The samples were characterized using SEM, XRD and Transmission Electron Microscope, TEM. The findings showed that only samples containing Mg sintered for 60 and 90 minutes in the hydrogen atmosphere exhibited liquid exudation. The amount of liquid exuded was more in samples sintered at 6000C than at 5500C; and in samples sintered for 90 minutes than in those sintered for 60 minutes. XRD results identified Al3Mg2 and Al12Mg17 as the compositions of the exuded liquids. Slight weight gains and swellings were observed in samples sintered in a nitrogen atmosphere due to the reaction of Al and N2 to form additional AlN in the compacts. The results suggest that longer sintering time, higher sintering temperature, lower compaction pressure and hydrogen atmosphere all promoted the exudation of liquids. The sintering parameter of the samples decreased with the amount of reinforcement, while the addition of Mg as a wetting agent enhanced the densification of the compacts.

Key words: Liquid Exudation, Powder Metallurgy, Sintering, Swelling, Wettability