Abstract
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.
Highlights
The grain refinement of aluminum by addition of Al–Ti and Al–Ti–B master alloys has been widely used and studied in recent years
On the Al substrate of Al–5Ti master alloy 1# a large number of blocky particles is uniformly distributed with the average length being roughly 25 μm (Table 1)
The results obtained are summarized as follows: (1) Significant fading is observed on longer holding with needle-like TiAl3 particles; (2) Master alloy 2# with mixed TiAl3 particles has relatively wider particles size distribution in comparison to other two master alloys, and TiAl3 particles are not completely dissolved within the holding time 30 min; (3) For master alloy 1# with blocky TiAl3 particles, fading is minimum, suggesting much less particle dissolution in comparison to other Al–5Ti master alloys
Summary
The grain refinement of aluminum by addition of Al–Ti and Al–Ti–B master alloys has been widely used and studied in recent years. Some researchers have considered the effect of microstructure of master alloys on their grain refining response [2,10] and even used special techniques to reduce intermetallic crystals in master alloys in size for the improvement of their efficacy [4,11,12]. The purpose of this investigation was to examine the effect of various microstructures on grain refining performance of Al–Ti master alloys produced by thermal explosion reaction in pure molten aluminum at different temperature
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