The Wettability of Silicon Carbide by Liquid Pure Aluminum and Aluminum Alloys

There have been strong moves in recent years to introduce the metal matrix composites concept into higher volume applications, notably the automotive field where large volume production and lower material costs are required. The wettability between reinforcing materials and base material is one of important factors for the strength of composites and its manufacture. The main objective of this paper is to establish a basic understanding of wetting phenomena in SiC/liquid aluminum and aluminum alloy systems. In the present paper, results from the sessile drop method are reported for the effects on the wetting angle, θ, of free silicon in the silicon carbide substrate and of alloying additions of silicon, copper or magnesium to the aluminum drop for the temperature range 700-900 or 1400°C in the titanium-gettered vacuum (1.3 x 10^-2 / 1.3 x 10^-3 Pa). Wetting angle, θ, was reduced by a factor as large as 2.8 for pure aluminum on reaction bonded, compared with sintered silicon carbide, attributable to partial dissolution by the aluminum of the 18 wt% free silicon present in the reaction- bonded material. For wetting of reaction-bonded silicon carbide, the addition of 5wt% silicon, copper or magnesium to the aluminum gave contact angle that decreased in the sequence Si → Cu → Mg, with the magnesium addition being the only one result in wetting (i.e. θ <90 ° ) for all conditions studied. These results may have implications for design of conditions for joining or promotion of infiltration of silicon carbide parts, preforms or arrays with aluminum alloy melts.