Microstructural evolution and microhardness of a melt-spun Al–5Ti–1B alloy during annealing

In the present work, microstructural evolution and microhardness of a melt-spun Al–5Ti–1B alloy during annealing have been investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) together with energy dispersive spectroscopy (EDS) and hardness testing. The phases present in the as-annealed Al–5Ti–1B alloy were determined to be α-Al, the equilibrium tetragonal TiAl3 and hexagonal TiB2, whereas only α-Al and TiB2 were identified in the as-spun alloy. Most of Ti in the α-Al solid solution rapidly precipitates by annealing at 500 °C and the low diffusivity of Ti in Al suppresses the coarsening of the TiAl3 precipitates with prolonged annealing time. Age hardening effect is not observed in the melt-spun Al–5Ti–1B alloy. The microhardness sharply decreases by annealing at 500 °C for 5 min and then slightly changes with prolonged time to 60 min. The microhardness keeps unchanged by annealing at 200 °C for 60 min, while annealing at 300 °C or higher temperatures causes a continuous decrease in microhardness. The microhardness of the as-spun Al–5Ti–1B alloy appears to be governed by a combination of Hall–Petch hardening from the α-Al cell size and solid solution hardening of the α-Al matrix, whereas the microhardness of the as-annealed alloy is mainly governed by a combination of Hall–Petch hardening from the α-Al cell size and particle radius dependent Orowan hardening.