Microstructure and mechanical properties of friction stir welded oxide dispersion strengthened AA6063 aluminum matrix composites enhanced by post-weld heat treatment

Oxide dispersion strengthened (ODS) AA6063 aluminum matrix composites (AMCs) sheets fabricated by a new method were successfully joined by friction stir welding (FSW) technique, and post-weld heat treatment (PWHT) was also performed to enhance the mechanical properties of the joints. Grain-size and maximum texture intensity obviously change in different weld zones. In the base metal (BM), the particles compose of complicated Al oxide (containing Al, O, Mg and Si) and AlFeSi intermetallics, and needle-shaped β″ precipitates were also observed. While, in the stir zone (SZ), the oxide particles mainly consist of MgAl2O4 instead of complicated Al oxide in BM, and β″ precipitates disappears. After PWHT, both MgAl2O4 and complicated Al oxide exist in SZ, and β″ were detected again. In the FSW joints, the microhardness values in SZ are far lower than those in BM. After PWHT, the microhardness values in SZ obviously increase, which was attributed to the contribution of β'' precipitates, Al oxides particles and AlFeSi intermetallics. The yield strength, ultimate tensile strength and elongation to fracture of PWHT samples are 291 MPa, 314 MPa and 5.0%, respectively, and joint efficiency for ultimate tensile strength is up to 92%, although a zigzag line was observed in SZ.