Studium zjemňování zrna nadeutetických slitin hliníku a křemíku

Abstract

Hypereutectic aluminum silicon alloys is aluminum silicon alloys with silicon content is more than 12.5 wt%. Hypereutectic aluminum silicon alloys are technological interest because of the advantageous properties imparted to them by the high volume fraction of hard eutectic and primary silicon particles. However, the morphology of the eutectic silicon particles is generally needle or plate-like and the primary silicon particles are large and faceted, producing stress concentrations that degrade the mechanical properties of the material. Therefore, it is necessary to refine the size of these particles and to modify their morphologies.

To refine primary silicon, phosphorus addition has been adopted as the most popular method which utilizes heterogeneous nucleation as a way to increase the number of primary silicon particles and, thus, reduces its average size. Phosphorus was used in the kind of Al-CuP master alloy or CuP master alloys. The refinement mechanism is well accepted that dissolved phosphorus combines with aluminum and forms aluminum phosphide (AlP) crystals. Aluminum phosphide crystals in the melt increase the amount of nucleation sites for silicon which solidifies later. The previous studies show that, refinement effects depend on phosphorus solubility and retained phosphorus. The particle size of primary silicon also depends on refinement temperature and refinement time. Using both of phosphorus and sodium compound could be established. They maybe have a reciprocal influence, for example sodium not only adsorbs on surface of silicon particles in eutectic phase but also adsorbs on surface of nucleation sites (AlP). Follow thermodynamic of crystallization process, crystallization process of silicon in eutectic phase only begins after crystallization process of primary silicon already finishes. Thus, the time for refiner addition into the melt is very important.

The present study is to provide a description of hyper-eutectic aluminum silicon alloys refinement, enabling a better understanding relation between phosphorus solubility and refinement mechanism. This study performed casting of aluminum silicon alloys of 18-20 wt.% silicon content with the refinement of master alloys (AlCuP). This master alloy was used to investigate the effects of the aluminum-phosphide on the primary silicon practices.

The focus of this study is on the application of AlCuP master alloy during manufacture process of piston of Kamaz automobile in the reality conditions of Vietnam industry. The alloys was used with 18-20 wt.% silicon content.