Abstract
Al-Ti-B master alloys are widely used in the aluminum industry as grain refiners for the control of the microstructure of the aluminum alloys. The SHS (self-propagating high-temperature synthesis) is an ex situ method that uses exothermic reactions to sustain the chemical reaction in a combustion wave. The advantages of SHS are the low energy requirement, simplicity and product purity. However, the raw material used has to be very pure, with a very small size leading to the necessity of a reactor with a protective gas to produce the reaction. The purpose of this investigation is to fabricate SHS master alloys with commercial standard raw materials, with lower purity and higher grain size without a reactor or protective gas in order to (1) decrease the price and (2) improve the productivity of master alloy manufacturing. The possibility of using cheap borated salts instead of expensive pure boron has been studied. Different compositions of aluminum master alloy have been developed. Bigger TiB2 grain size has been obtained when using bigger commercial raw materials. Larger titanium powder can produce an aluminum master alloy with a maximum of 30% of aluminum without reactor. In comparison, SHS reaction is much more difficult when using finer titanium powder.
Highlights
Addition of titanium-boron master alloys to molten aluminum produces fine, equiaxed grains after solidification, which otherwise tends to be coarse and columnar [1,2,3,4,5]
The aim of this work is to establish the effect of KBF4 and Na2B4O7 as raw materials and NaCl/KCl salts as flux agents to obtain an Al-Ti-B refining master alloy made by SHS using Ti and B powders with quite large particle size, impurities at different concentrations and with and without a protective atmosphere
The results presented are part of a work aimed at developing low cost refining master alloys presenting a good refining effect
Summary
Addition of titanium-boron master alloys to molten aluminum produces fine, equiaxed grains after solidification, which otherwise tends to be coarse and columnar [1,2,3,4,5]. A fine, equiaxed grain structure imparts to casting materials, high toughness, high yield strength, excellent formability, good surface finish and improved machinability [6,7]. The use of grain refining master alloys in casting of ingots, billets and strip, has become a common practice in aluminum foundries worldwide. The grain refinement of aluminum alloys, by melt inoculation, is generally achieved by introducing into the melt Al–Ti–B master alloys [9,10,11,12], which typically consist of TiAl3 and TiB2 particles in an aluminum matrix.
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