Abstract
The tensile properties and microstructures of AA6061/Si3N4 particle composites fabricated by pressureless infiltration under a nitrogen atmosphere were analyzed. In addition, the control AA6061 without Si3N4 particles fabricated by the same method was investigated to separate the effect of Si3N4 particle addition. It was found that AlN particle layers formed on the surface of Al particles in the powder bed, which replaced the Mg3N2 coated layers through the following reaction: Mg3N2 + 2Al → 2AlN + 3Mg. Thus, the spontaneous infiltration results from a great enhancement of wetting via the formation of Mg3N2 by the reaction of Mg vapor and nitrogen gas. The increased tensile strength and 0.2 pct offset yield strength in the control AA6061 were largely due to fine AlN particles formed by the aforementioned in situ reactions, as compared to commercial AA6061. In the composite reinforced with Si3N4 particles, of course, the AlN was also formed through the following additional reaction at the Si3N4 particle/Al melt interfaces: Si3N4 + 4Al → 4AlN + 3Si. However, this AlN may not contribute to the increase in strength because its formation is compensated by the consumption of Si3N4 particles. Consequently, the strength increase of the composite fabricated by the present method is attributed to the fine AlN particles formed in situ, as well as the fine reinforcing Si3N4 particles, as compared to commercial AA6061.
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