Analysis of the structure and resulting mechanical properties of aluminium extrusions containing a charge weld interface

Abstract

This work describes a detailed study of the effect of the presence of a charge weld transition zone on the failure mode and local effective mechanical properties of the extrudate. To this aim a dedicated die was designed for which the flow pattern was such that the effect of the charge weld zone could easily be isolated. The effect of the charge weld zone on the damage and failure evolution during testing of tensile samples loaded to various strain levels was demonstrated and analysed in detail. The evolutionary geometry of the bond plane was visualised by serial sectioning of the extrudate followed by metallographic characterisation. An even better insight was obtained by in-situ observations during tensile testing of samples containing a weld seam. It is shown that the mechanical performance is largely controlled by the density of the oxide particle population at the charge weld boundary. Crack initiation is determined primarily by the central weld seam interface segment containing a more or less fractured layer of oxides. The peripheral sides of the weld seam region failed in a ductile manner characteristic of regular base material. The main conclusion of the work is that the flow pattern in the die determines the length and shape of the charge weld interface as well as the drop in mechanical properties due to fracturing of the oxide layer.