EVALUATION OF THE EFFECT OF MODIFIERS AND REFINERS ON THE MECHANICAL BEHAVIOR AND SHRINKAGE OF AL7SIXMG ALLOYS

摘要

The use of Al-Si alloys is taken into consideration when good castability and good corrosion resistance are needed. Commercial Al-Si alloys span the hypoeutectic and hypereutectic ranges up to about 25% Si. Small additions of Mg make these alloys heat treatable. In this case, the hardening is attributed to the formation of Mg_(2)Si compound. The eutectic structure of Al-Si alloys can considerably be affected by cooling rate and modifying additions. With an effective modification treatment, the silicon assumes a fine fibrous structure and the mechanical properties of the casting increase substantially. Nowadays, the modification process of hypoeutectic Al-Si alloys with elements such as Na, Sr and Sb has become a standard foundry practice. The technique of the thermal analysis is widely accepted to control such modification degree as well as grain refinement in the aluminium foundry. The presence of modifier can usually be related to the shape of the eutectic arrest in the cooling curve. However, the most important question is to choose an appropriate parameter between those of time and temperature to characterise modification degree efficiently.