Application of finite element method in the hot extrusion of aluminium alloys

摘要

The major objective of the present paper is to explore the complicated interactions between die design, forming parameters (i.e. ram speed, container temperature, billet temperature and extrusion ratio) and the product qualities (extrudate shape, surface condition and microstructure) by the use of finite element modelling (FEM). The various models (such as recrystallisation, damage criteria, etc.) have been integrated into the commercial codes, FORGE2~(~R) and FORGE3~(~R), through user routines. The physical recrystallisation model proposed by Sellars and Zhu [Mater. Sci. Eng. A280 (2000) 1] and Vatne et al. [Acta Mater. 44 (1996) 4463] have been compared. The predicted distributions of the volume fraction recrystallised were also compared with the experimental results from the literature. The influences of forming parameters on the occurrence of surface cracks were studied by the combination of the Taguchi method with the FEM. It was found that the choked die could significantly reduce the possibility of producing surface cracks. Through simulating a shape extrusion process using two different die structures, it was found that the use of an expansion chamber can significantly reduce the degree of non-uniformity in terms of the extruded product shape and properties. The character of the complex material flow is also identifiable, which is very useful to help improve die design.