Experimental Verification of Progressive Method for Porosity Prediction

摘要

The final integrity of a casting is greatly influenced by the presence of porosity. Progressive way to predict presence of porosity is the use of various simulation softwares. In most of these programs today, porosity prediction is limited to macro-shrinkage porosity which corresponds to the contraction of the metal during solidification. This approach does not take into account for gas and interdendritic shrinkage porosity, and yet, these types of porosity are the main factors affecting mechanical properties of cast aluminium alloys, in particular fatigue resistance and toughness. The main aim of submited article is to verify possibilities of this promising and complex method to predict porosity. Various factors will be discussed: melt temperature, mold temperature, mold material and also used alloy (in next phase of experiments also inoculation and modification). A calculation of advanced porosity prediction was performed for an aluminium alloys with help of advanced porosity module included in ProCAST sotware. This calculation takes into account all basic phenomena, which are at the origin of micro and macro porosity. For porosity analysis was used specific casting mold - Sanduhrprobe. Shape of mold is designed in unique way, so in solidification phase is induced three types of voids, at a free surface, the level of liquid decreases as solidification proceeds (piping), within closed liquid pockets (hot spots), a macropore surrounded also by microporosity will be present. Material used in experiment is not loaded from software database, because results could be distorted, to achieve precise results, we used thermal analysis to get accurate data about particular used alloys. Important solidification events, which affects porosity formation, such as recalescence and nucleation undercooling temperature, coherence point and rigidity point have been evaluated using cooling curve and its first derivate curve obtained from thermal analysis of a sample.