Formation of die lines during extrusion of AA6063

Abstract

The die line phenomenon during extrusion of AA 6063 has been investigated and the effects of temperature and strain rate established. The influence of die land length on the surface generated features was also determined. The results indicate that the surface formation mechanism is one of generation and modification; the surface is generated on the leading edge of the die land in the absence of oxygen and interacts thereafter with the remainder of the die land, resulting in material transfer between extrudate and die land, thus increasing the surface roughness. Two mechanisms were identified, both of which involved extrudate die land interaction. The aluminium film on the forward portion of the die land was observed to be more stable and its morphology wasfound to relate directly to the die line features. From these trials, optimum process conditions together with a minimum die land length were identified. Processing at the optimum conditions continued to generate die lines, but these were observed to be finer and less deep, and were termed ‘microdie lines’. The origin of the micro die lines was observed to stem from the structure formed by deformation and the nature of the shear zone.

MST/1108