Oxidation of the AlSi6Cu4 alloy and AlSi6Cu4-graphite particles composite at the elevated temperatures

Oxidation process of AlSi6Cu4 alloy as a composite matrix and of AlSi6Cu4 / 8 vol.% graphite particles composite was investigated. Composites were prepared by stirring method for suspension obtaining and by squeeze casting of the suspension. This process was examined by testing specimens annealed during up to 1000 hours at 573 K and 673 K in air atmosphere. The average oxidation state, oxide layer thickness and hardness of examined materials were measured during the annealing time. Obtained results imply the following conclusions: composite oxidizes faster than matrix alloy at both temperatures what is confirmed by higher weight gains and thicker oxide layer. The rate of oxidation of both materials gradually slows down at both temperatures. At initial stages of annealing at 673 K the rate of oxidation of both materials is much higher than that at 573 K. With increasing time of annealing the ratio of oxidation rate at 673 K to the one at 573 K comes down. Hardness of the composite is lower than that of matrix alloy before and during annealing at both temperatures. Drop in hardness at both 573 K and 673 K is the same for matrix and composite, and after about 100 hours the hardness no longer descents.