Microstructure characteristic and grain refining performance of Al–5Ti–1B master alloy improved by copper mould die casting

Abstract

The influence of subrapid solidified processing parameters on the microstructure characteristic and grain refining efficiency of Al–5Ti–1B master alloy has been studied. The results show that the mean size of Al₃Ti particles in Al–5Ti–1B master alloy decreases significantly after copper mould die casting. The morphology of Al₃Ti particles changed from plate-like to blocky and petaloid. Compared with conventional Al–5Ti–1B master alloy, the phase constitution of subrapidly solidified Al–5Ti–1B master alloy does not change, and the improved master alloy shows a better grain refining efficiency. The microhardness of the pure aluminium refined by conventional and improved Al–5Tu–1B obeys the Hall–Petch relation, and the material constant k_H is in the range of 84·02–91·80 MPa μm^1/2. The mechanisms of grain refinement of aluminium by inoculation with improved Al–5Ti–1B master alloy are discussed based on the duplex nucleation theory and growth restriction effects in aluminium alloys.