Fabrication and characteristics of AA6061/Si3N4p composite by the pressureless infiltration technique

The tensile properties and microstructures of AA6061/Si3N4 particle composi tes fabricated by pressureless infiltration under a nitrogen atmosphere wer e analyzed. In addition, the control AA6061 without Si3N4 particles fabrica ted by the same method was investigated to separate the effect of Si3N4 par ticle 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 spont aneous infiltration results from a great enhancement of wetting via the for mation 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 w ere largely due to fine AlN particles formed by the aforementioned in situ reactions, as compared to commercial AA6061. In the composite reinforced wi th Si3N4 particles, of course, the ALN was also formed through the followin g additional reaction at the Si3N4 particle/Al melt interfaces: Si3N4 + 4Al --> 4AlN + 3Si. However, this AlN may not contribute to the increase in st rength because its formation is compensated by the consumption of Si3N4 par ticles. 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.