Effect of Temperature on Microstructure and Fracture Mechanisms in Friction Stir Welded Al6061 Joints
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2017, ASM International. Aluminum and its alloys are widely used in different industries due to such attractive properties as adequate strength, ductility, and low density. It is desirable to characterize welds of aluminum alloys obtained using friction stir welding at high temperatures. Al-to-Al (both 6061-T6) butt joints are produced by friction stir welding at tool rotation speed of 1600rpm and four levels of tool advancing speeds: 250, 500, 750, and 1000mm/min. Microstructural properties of the different welds are investigated. Observed are noticeable differences in microstructure characteristics between the various weld zones. Mechanical properties of these welded joints are characterized under tensile tests at temperatures of 25, 100, 200, and 300C, at a constant strain rate of 103/s. The optimum microstructural and mechanical properties were obtained for the samples FS welded with 1600rpm tool rotation speed at 1000mm/min tool advancing speed. The studied welds exhibited yield strength, ultimate tensile strength, and strain to failure with values inferior of those of the base material. Observations of postmortem samples revealed that in the temperature range of 25-200C the locus of failure originates at the region between the thermo-mechanically affected zone and the heat-affected zones. However, at higher temperatures (300C), the failure occurs in the stir zone. A change in the crack initiation mechanism with temperature is suggested to explain this observation.
