Towards in-process scrap reduction in aluminum extrusion: A multiscale investigation of charge-weld integrity

Charge welds in ‘continuous’ billet-to-billet extrusion processes are commonly associated with substandard material properties, leading to conservative industrial scrap practices. Despite the prevalence of this problem, limited understanding exists regarding governing mechanisms in terms of microstructural and mechanical evolution across the charge-weld zone under real-world processing conditions. This study presents a comprehensive multiscale investigation of charge-weld integrity in hollow AA6082 profiles using a combined experimental and numerical approach. A large number of full-scale industrial extrusion trials were carefully conducted at varying ram speeds, followed by systematic microstructural and mechanical characterizations of the weld zone. The experimental findings reveal a gradual increase in charge-weld strength and ductility along the extruded profile. This is primarily attributed to a reduction in the density and size of oxide-induced grooves and pits at the weld interface between two succeeding billets dispersed into the extruded profile. To understand the governing mechanisms at continuum scale, a finite element model was developed using QForm-Extrusion software. The Kolpak’s semi-empirical film theory-based model was incorporated to investigate how thermo-mechanical history and ‘local’ conditions influence charge-weld integrity. The numerical model effectively captured important trends of charge-weld integrity, identifying regions where weld properties progressively recovered to the levels of parent material. Our findings show that a substantial portion of the charge-weld zone provides adequate material integrity, which may call for less conservative scrap standards in industry. Overall, this work advances the fundamental understanding of charge-weld formation, offering a pathway to optimizing material yield towards more efficient manufacturing of aluminum products.