Nucleation and Growth of Primary Silicon Crystals in AlSi Alloy after Modification with CuP and Overheating to a Temperature of 920°C

Abstract:

The article describes the process of crystallization of an AlSi17Cu5 (the A3XX.X series according to ASTM standard) alloy which has been modified with 0.05 wt. % P (CuP10 master alloy) and overheated to a temperature of 920°C. It has been shown that, so-called, "time-temperature treatment" (TTT) of alloy in the liquid state, which consists in overheating the alloy to a temperature above T_liq (about 250-300°C), holding at this temperature and rapid cooling, alters the morphology of primary silicon crystals. By the ATD method of thermal analysis, the characteristic temperature of crystallization (T_liq., T_Emin., T_Emax., T_E(Cu), T_E(Fe), T_sol.) were determined, and exothermic effects of the modifier and high-degree overheating on the crystallization course of the investigated alloy were examined. A new mechanism of proeutectic crystallization of the a(Al, Me=Cu, Fe) dendrites was proposed. The course of this process is dynamic enough to promote, due to local undercooling, the evolution of heat, which in the ATD curve appears as a well visible additional exothermic effect designated as T_X. It is due to the presence in the liquid alloy of microregions with varied content of dissolved silicon.

• Periodical: Solid State Phenomena (Volume 212)
• Pages: 237-242
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.212.237
• Online since: December 2013
• Authors: Jaroslaw Piątkowski
• Keywords: Hypereutectic Silumins, Modification, Overheating, Proeutectic Crystallization

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