Performance of Al-6063 primary and secondary billets used in hot aluminum extrusion

The service life of tooling plays an important part in the economics of the extrusion process. A number of causes are considered responsible for initiating damage to the dies before its designated life is reached. Apart from other factors such as die design and manufacturing, heat treatment, working conditions, etc, the performance of the die can directly be related to the billet quality used in the extrusion press. The purpose of this paper is to investigate the effect of Al-6063 billet source (primary or secondary) on extrusion die failure, based on microstructural investigation. A secondary (remelt) billet cast in-house at a local extrusion plant is compared with a primary (smelter) billet by applying different material characterization techniques, including optical microscopy, Vickers microhardness measurement, X-ray diffraction (XRD) analysis, and energy dispersive spectroscopy (EDS). It is observed that a secondary billet has a comparatively coarse grain structure, nonhomogeneous distribution of secondary phases, inclusions, and high hardness that can be associated with poor casting and homogenization practice. In view of present results, some suggestions during in-house billet preparation of secondary billets have been formulated for improved die service life.