Influence of Si content on thermal expansion characteristic of Al-Si alloys

The objective of this study was to find out how Si precipitation affects the linear thermal expansion behaviors of Al-Si alloys with various Si content. These Al-Si alloys were manufactured by gravity casting using 99.98 wt-% pure Al and 98.5 wt-% Si pellets. Solution treatment was carried out at 530 degrees C for 10 h for each specimen. As-quenched specimens were subjected to microstructure observation and linear thermal expansion analysis. Si precipitation and additional linear thermal expansion occurred at lower temperature when Si content was increased to 9.5 wt-%. The activation energy of Si precipitation was also lower when Si content was higher. Eutectic Si reduced diffusion distance and acted as a nucleation site of dissolved Si atoms in the Al matrix during aging. These Si phases decreased Si precipitation temperature and activation energy of Si precipitation.