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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.57  No.7 (2016)  >  pp.1124-1133

MATERIALS TRANSACTIONS
<<Previous article Vol.57  No.7 (2016)   pp.1124 - 1133 Next article>>

Effects of Partial Remelting on Microstructure of Al-Si-Ti Bulk Alloy Prepared by Cold Pressing Mixed Powders

Y.J. Wang1), T.J. Chen1), S.Q. Zhang1), Y.H. Qin1), X.Z. Zhang1)
1) State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology

The microstructural evolution and phase transformations have been investigated during the partial remelting of a bulk alloy prepared by the cold pressing of A356, pure Ti and pure Al powders. A dropping experiment was used to investigate the reaction kinetics of Ti powders and the Al matrix simultaneously. The results show that a semi-solid microstructure with fine and spheroidal primary α-Al particles suspended in the liquid phase could be obtained after the bulk alloy was heated to 595℃ for 30 min. The microstructural evolution process was divided into four stages, involving the transformation of the powders into primary particles, the formation of a liquid phase and the increase in its amount, which results in the formation of a continuous liquid layer, the rapid coarsening of the primary particles and the increase in the liquid phase amount, and the final coarsening of the primary particles. Chemical reactions between the Ti powders and the Al element in the matrix occurred simultaneously. Next, core-shell structured, reinforced particles composing both an intermetallic shell and a soft Ti metal core formed in situ. The compact shell subsequently ruptured and peeled off when its thickness increased to a given value for a given size of Ti powder particles. Finally, the Ti powders were consumed completely because of the formation and the subsequent peeling of the shell. Results of the dropping simulation experiment show that the reaction product layer grows in a linear kinetic manner characterized by an activation energy of 374 kJ/mol.


Keyword:
microstructural evolution, Al-Si-Ti bulk alloy, partial remelting, core-shell structured particle, Al matrix composite

Received: February 25, 2016
Accepted: April 15, 2016 , Published online: June 25, 2016

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