Microstructure and Mechanical Properties of Ultrahigh-Speed Friction-Stir-Welded Joints of In Situ Al3Zr Particle-Reinforced Aluminum Matrix Composite Sheets

Herein, in situ Al3Zr + 6082Al aluminum matrix composite sheets subjected to ultrahigh-speed friction stir welding (FSW) at welding and stirring-head rotation speeds of 200 mm min(-1) and 11 000, 13 000, or 15 000 rpm, respectively, are focused on. X-ray diffraction, electron microscopy, energy-dispersive spectrometry, microhardness testing, and tensile testing are used to investigate the microstructures and mechanical properties of the welds. The weld nugget zone (NZ) of the high-speed FSW joint of the Al3Zr + 6082Al matrix composite sheet comprises mainly equiaxed recrystallized grains, the thermomechanically affected zone comprises equiaxed recrystallized grains and elongated plastically deformed grains, and the heat-affected zone comprises recrystallized grains. Results show that the FSW joint formed at 13 000 rpm and 200 mm min(-1) is extremely well formed and has a compact and uniform structure. The microhardness of the 13 000 rpm FSW joint is highest at an NZ hardness and tensile strength of 128.08 HV and 153.7 MPa (87% of that of the base metal), respectively.