Microstructural Evolution, Powder Characteristics, Compaction Behavior and Sinterability of Al 6061–B₄C Composites as a Function of Reinforcement Content and Milling Times

Al 6061_100–x–x wt % B₄C (x = 0, 5, 10, 20, 30 and 40) composites, prepared by mechanical alloying and compacted at room temperature, have been used for the present investigation. The effects of B₄C content and milling time on the powder morphology, powder particle size, and other powder characteristics such as the apparent density, tap density, flow rate, cohesiveness, and hausner ratio are systematically investigated. The steady state of milling process is determined by observing the correlation between apparent densities and milling time explained by the morphological evolution of the powder particles during the milling process. The Hausner ratio (HR), estimated to evaluate friction between the particles, decreases with an increase in milling duration and B₄C content due to the changes in morphology and hardness of the powders. The compressibility behavior of post-compacts as a function of compaction pressure and the B₄C content was analyzed by using several linear and non-linear powder compaction equations. The linear Panelli and Ambrozio Filho, and non-linear Van Der Zwan and Siskens equations give the highest regression coefficients. The results are explained in terms of the plastic deformation capacity and plastic deformation coefficient of the powders, which are influenced by the hardness and the morphology of the powder. After compaction, the supersolidus liquid phase sintering was performed at various temperatures (585, 610 and 630°C) under high purity nitrogen atmosphere. The results revealed that the sinterability was degraded by increasing the reinforcement content, particularly above 10 wt % B₄C. Neutron radiography measurements conducted on the rolled composite sheet have revealed the uniform distribution of B₄C particles in the composite.