Effects of Rotation Speed and Forward Speed on Stir Zone Formation During Friction Stir Processing of Al-7Si-0.3Mg Alloy

Abstract

Friction stir processing (FSP) could potentially be used to modify and refine the microstructures of aluminium alloy castings for use as structural rather than non-structural components. However, there is currently an insufficient understanding on how FSP parameters affect the individual and combined flows forming the various regions in the processed zone during FSP in literature. In this study, a cast Al-7Si-0.3Mg alloy was used to provide readily identifiable processed zones. A series of FS experiments covering a wide range of tool forward (ν) and rotation (ω) speeds were conducted followed by the measurement of individual and combined stir zone areas. We have identified that the deformation of α(Al) dendrites and eutectic Al-Si sheared by the pin resulting in fine Si particles evenly distributed in α(Al) matrix was a major mode of flow. Another mode of flow was associated with the material merely dragged into the FS zone and, as a result, Si-particle clusters remained. The basic modes of material flow did not change but the volume of each individual flow and combined flow volume depended on both ν and ω. The trends observed on the present data can explain how pin rotation relates to the material transportation mechanism and the associated torque (M) required. The present data also explains how ν, not ω, relates to specific energy (E_s) and the volume of the total stir zone.