MICROSCOPIC EXAMINATION OF THE INTERFACE REGION IN 6061-AL/SIC COMPOSITES REINFORCED WITH AS-RECEIVED AND OXIDIZED SIC PARTICLES

Aluminum (6061) matrix composites reinforced with different SiC particles were processed. Black SiC particles were used in their as-received form or after artificial oxidation, leading to a 50-nm-thick SiO2 layer surrounding the SiC particles. The manufacturing route used was the compocasting technique, which allows maintenance of the semisolid slurry at relatively low temperatures (<650 °C) during the incorporation of the reinforcement. Before squeeze casting, the liquid alloy is held at 700 °C for 5 to 10 minutes. The interface between the aluminum matrix and SiC was characterized by transmission electron microscopy (TEM). Results show that no reaction takes place during compocasting between the as-received SiC particles and the molten aluminum. This is a consequence of the low temperatures and short holding times in the liquid state of the 6061 alloy, possible with this process. Prolonged holding at 800 °C of this material leads to extensive formation of A14C3. In the case of artificially oxidized SiC particles, the SiO2 layer surrounding the SiC particles reacts with the molten Al-Mg-Si alloy to produce MgAl2O4. However, the amount of Mg from the base alloy lost to form this spinel phase is not sufficient to prevent age hardening of the material. © 1990 The Metallurgical of Society of AIME.