Surface Segregation and Surface Defect Formation During Aluminum Billet Casting

摘要

In this paper the surface zone formation during direct chill casting of aluminum billets, produced by the air slip technology, is discussed. The shell zone depth and compositions have been quantitatively studied, and the surface microstructures of 6060, 6005 and 6082 alloys are compared and coupled to surface appearances. The understanding of the results is based on the exudation of liquid metal through the mushy zone and the fact that the exudate liquid is contained within a surface oxide skin, and the oxide skin movements are coupled to various surface appearances. The major defects that occur during billet castings are different kinds of vertical drags or horizontal bandings, also called lapping. The structures coupled to these defects and theories for their formation are discussed.