Performance Comparison of Al–Ti Master Alloys with Different Microstructures in Grain Refinement of Commercial Purity Aluminum
Three types of Al–5Ti master alloys were synthesized by a method of thermal explosion reaction in pure molten aluminum. Performance comparison of Al–5Ti master alloy in grain refinement of commercial purity Al with different additions (0.6%, 1.0%, 1.6%, 2.0%, and 3.0%) and holding time (10, 30, 60 and 120 min) were investigated. The results show that Al–5Ti master alloy with blocky TiAl3 particles clearly has better refining efficiency than the master alloy with mixed TiAl3 particles and the master alloy with needle-like TiAl3 particles. The structures of master alloys, differing by sizes, morphologies and quantities of TiAl3 crystals, were found to affect the pattern of the grain refining properties with the holding time. The grain refinement effect was revealed to reduce markedly for master alloys with needle–like TiAl3 crystals and to show the further significant improvement at a longer holding time for the master alloy containing both larger needle–like and blocky TiAl3 particles. For the master alloy with finer blocky particles, the grain refining effect did not obviously decrease during the whole studied range of the holding time.
Microstructures of Al–Al3Ti functionally graded materials fabricated by centrifugal solid-particle method and centrifugal in situ method
Methods of fabrication by centrifugal casting for functionally graded materials (FGMs) can be classified into two categories on the basis of the relationship between the process temperature and the liquidus temperature of a master alloy. They are the centrifugal solid-particle method and centrifugal in situ method, which could be carried out at process temperatures lower and higher than the liquidus temperature of the master alloy, respectively. In a previous study, it was found that the microstructures of Al–Al3Ti FGMs fabricated by the centrifugal in situ method processed at 1600 °C were different from those fabricated by the centrifugal solid-particle method processed at 800 °C. Although it is expected that the FGMs fabricated by the centrifugal in situ method processed at approximately the liquidus temperature should show extraordinary microstructures, those microstructures have not been observed. In this study, the microstructures of Al–Al3Ti FGMs fabricated at 1000 °C (centrifugal solid-particle method) and 1200 °C (centrifugal in situ method) were investigated.
Intermetallic particles in Al–Ti–B–type master alloys for grain refinement of aluminium
AbstractBoride and titanium aluminide particles from various master alloys have been studied by metallography, electron microscopy, and X-ray diffraction in order to reveal the role of these particles in the grain refinement of aluminium. It has been found that TiB2, (TiAl)B2, AlB2J and TiAl3 form during the production of the master alloy. The size and morphology of the borides is quite independent of the production of the master alloy. A superstructure in the TiB2 lattice develops with holding time, indicating a stable ternary Ti–Al–B phase. A preferred orientation relationship was found to exist between the Al3Ti crystals and the aluminium matrix.