Friction Stir Processing of Aluminum Alloys

• Main Author: Sun, Ning
• Other Authors: Makhlouf M. Makhlouf, Committee Member
• Format: Others
• Published: Digital WPI 2009
• Subjects: FSP; microstructure; mechanical properties
• Online Access: https://digitalcommons.wpi.edu/etd-theses/603; https://digitalcommons.wpi.edu/cgi/viewcontent.cgi?article=1602&context=etd-theses

Friction stir processing (FSP), a solid-state post-processing technique that can provide localized modification and control of microstructures in near-surface layers of metallic components is developed based on the principles of friction stir welding (FSW). In this study, FSP was carried out in two phases. In Phase I, FSP was applied to one inch thick, sand casting A206 aluminum and 0.25 inch A367 bending fatigue sample. Optical microscope, SEM and EDS measurements have been performed to reveal a homogenous microstructure in the stirred zone, in which the porosities were quantitatively reduced, the second phase particles have been broken up and distributed in the Al matrix and there were some new components generated. Thermocouples have been applied to acquire the temperature gradient and thermo history during FSP. A range of material properties, including hardness and tensile measurement in A206, and bending fatigue test in A367 were examined. FSP resulted in an increase in hardness of the nugget compared to the hardness profile of the T4 condition. A significant improvement of the ductility of A206 was found after FSP compared to the ductility of T4 A206, but the FSP process slightly reduced the strength of A206. In Phase II, FSP was used for composite fabrication in the top layer of A206 substrate. The discontinuously reinforced aluminum (DRA) which contained 15% weight percent SiC was introduced into one inch thick sand cast A206 substrate. The surface composite layer is well bonded to the aluminum alloy substrate. Defects were not visible validating that FSP is an effective way for composite fabrication in Al cast alloys.