The goal of this study was to develop composites based on an Al-Si alloy (Alumix-231) with the addition of 5 to 20 vol. percent of fused silica, to reduce the coefficient of thermal expansion (CTE) in comparison to that of the matrix (Alumix-231), keeping the composite light and without impairing its physical properties, such as density and hardness. The composites were developed by powder metallurgy, first pressed at 700 MPa, and then sintered at temperatures between 565 and 575 degrees C for 90 min (T1 condition). The best results, in terms of reduced thermal expansion, were achieved after liquiq-phase sintering at 565 degrees C. Composites with the addition of 15 and 20 vol. percent of fused silica exhibited CTEs, as low as, 13.70 and 12.73 x 10(-6) degrees C(-1) (between 25 and 400 degrees C), a reduction of 29.9 percent and 34.8 percent, respectively, compared to neat Alumix-231. Furthermore, the density and hardness of these composites were not negatively affected, as these properties presented only a small decrease, not exceeding 6 percent and 5 percent, respectively. Then, samples sintered at 565 degrees C were artificially aged at 160 degrees C for 8 h (T6 condition), and MMCs-15 and 20 vol. percent exhibited an increase in hardness of about 94,12, percent and 64,71 percent, compared to T1 samples. Regarding thermal expansion, there was a reduction of CTEs, compared to the aged neat alloy, of 27 percent and 32 percent, respectively. Alumix-231 is a promising new alloy and fused silica, which has never been used before to reduce its thermal expansion, has shown to be a ceramic with promising applications as a filler in Alumix-231-based matrix composites, due to its thermal expansion close to zero. As such, the results obtained showed that Alumix231/fused silica composites are promising materials for automotive applications and new candidates to replace heavy cast iron components.