Characteristics of defect bands and their formation mechanisms in A356 wheel fabricated by horizontal squeeze casting

Abstract

Based on the opinion that a decreasing solid fraction gradient in the cross-section develops during the intensification stage, the shear stress in the solidifying alloy was analysed, and a mechanism for dilatant band formation was discussed. That is, when the shear stress at one position of the stable grain network reaches a critical value, the network collapses and the band forms. The characteristics of defect bands at different locations of an A356 wheel fabricated by horizontal squeeze casting were then studied. Three types of defect bands, i.e. skin related band, dilatant band and separate band, were observed. Combining the process and conditions of defect band formation, several types of defect bands in the casting were discussed. Furthermore, the influence of the structural characteristics of castings on the defect bands, including thickness, geometry and location, was summarised.

Keywords:

• Defect band
• Formation mechanism
• Shear stress
• A356 wheel
• Horizontal squeeze casting
• Structural characteristic

Acknowledgements

The authors gratefully acknowledge financial and experimental support from L. K. Technology. The authors would also like to acknowledge experimental assistance from Mr B. Wang and Mr P. Zhou.