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.