Formation mechanism of surface segregation in aluminum alloy die castings

摘要

The effects of casting conditions on segregation ofsolute elements at die castings surface were investigated and theformation mechanism of segregation at die castings surface isdiscussed using two kinds of alloys. JIS-ADC 10 and Al-4.5masspercent Cu alloy have been cast by laminar flow die castingprocess. The segregation of solute elements at the surface of diecastings were examined by SEM and EPMA technique. In the caseof ADC 10, the concentration of Si, Cu, Fe and Mg segregated atdie casting surface is more than two times in comparison with theaverage value of ADC 10 alloy die castings. The segregation of Cu,Fe and Mg increases with increasing casting pressure anddecreasing casting temperature. And segregation of these elementsdecreases by decreasing shot velocity and intensified pressure timelag. However, segregation of Si is affected by only castingtemperature and concentration of Si at die casting surfaceincreased with increasing the casting temperature. It has beenrevealed that the segregation of Cu at the surface of AI-4. 5masspercentCu alloy die castings is affected with solidificationratio of the surface layer and timing of intensified pressure. Theformation of surface segregation can be occurred by the squeezeout of interdendritic solute-enriched liquid into the gap betweendie casting and mold surface by intensified pressure.