The influence of process parameters and themomechanical history on streaking defects in AA6060 extrusions

Streaking is a common surface defect on architectural extrusions. The current study investigates the effect of processing parameters and thermomechanical history on the surface finish of a streaked AA6060 extrusion. Streaked profiles were intentionally produced via extrusion using a die with internal geometry deliberately designed to produce thermomechanical variation in specific regions of the profile geometry. Extrusions were conducted at various ram speeds and the profiles were given an anodization pre-treatment process to reveal streaking in the designated regions. Thermomechanical variation was analyzed using the “ALE” code HyperXtrude. The surface profile and roughness of the treated and mill finish extrudates were analyzed using optical profilometry. The presence of the streaks were associated with strain rate variability as determined by the die geometry, independent of the ram speed. The streaked regions of the profile were found to be more recessed compared to the bulk regions.