アルミニウム合金ダイカストの表面偏析発生機構

Abstract

The effects of casting conditions on segregation of solute elements at die castings surface were investigated and the formation mechanism of segregation at die castings surface is discussed using two kinds of alloys. JIS–ADCIO and Al–4.5 mass% Cu alloy have been cast by laminar flow die casting process. The segregation of solute elements at the surface of die castings were examined by SEM and EPMA technique. In the case of ADC 10, the concentration of Si, Cu, Fe and Mg segregated at die casting surface is more than two times in comparison with the average value of ADC 10 alloy die castings. The segregation of Cu, Fe and Mg increases with increasing casting pressure and decreasing casting temperature. And segregation of these elements decreases by decreasing shot velocity and intensified pressure time lag. However, segregation of Si is affected by only casting temperature and concentration of Si at die casting surface increased with increasing the casting temperature. It has been revealed that the segregation of Cu at the surface of Al–4.5 mass%Cu alloy die castings is affected with solidification ratio of the surface layer and timing of intensified pressure. The formation of surface segregation can be occurred by the squeeze out of interdendritic solute-enriched liquid into the gap between die casting and mold surface by intensified pressure.