Dendrite and silicon particle refinement using aluminum-insoluble elements in hypoeutectic aluminum silicon alloys.

摘要

For hypoeutectic Al-Si alloy castings, minimizing dendrite arm spacing and modification of the secondary Si particles is the most effective means for maximizing strength and ductility. Dendrite refinement can be affected by microalloying with selective elements that promote interfacial instability through constitutional and thermal supercooling. The microalloying elements used in commercial Al alloys A319 and A356 are 0.5 to 1.0 wt% of Sb, Bi, In and Sn, which have little or no solubility in Al, i.e. they have extremely low distribution coefficients. Significant refinement of the dendrite structures (decreasing DAS) and the modification of eutectic Si particles were obtained with the additions of the microalloying elements Sb and Bi. Also the mechanical properties (strength, elongation and impact toughness) were significantly improved with Al-insoluble elements. A dendrite-growth model, based on the Mullins-Sekerka interfacial stability theory, further enhanced by Langer and Muller-Krumbhaar, which uses the thermal supercooling and interfacial instability resulting from solute trapping due to non-steady state growth conditions, is proposed to account for the results.Dept. of Mechanical, Automotive, and Materials Engineering. Paper copy at Leddy Library: Theses u26 Major Papers - Basement, West Bldg. / Call Number: Thesis1996 .W46. Source: Masters Abstracts International, Volume: 34-06, page: 2457. Adviser: W. V. Youdelis. Thesis (M.A.Sc.)--University of Windsor (Canada), 1996.