Study of the mechanism of grain refinement of aluminum after additions of Ti- and B-containing master alloys
- Stockholm Univ. (Sweden)
- Metalworking Tech., Inc., Johnstown, PA (United States)
A highly sensitive thermal analysis technique has been used to study the mechanisms of grain refinement in high-purity aluminum. Additions of Al-Ti-B master alloys were made both below and above the peritectic concentration in reference to the Al-rich corner of the binary Al-Ti phase diagram (0.15 pct Ti in solution). The experiments were conducted at various times after the addition of grain refiner. From the results, except for formation of TiB[sub 2], no effect of boron on the Al-rich portion of the binary Al-Ti phase diagram can be observed. With hypoperitectic additions of Al-Ti-B master alloys, TiB[sub 2] Particles are the most frequent nucleant for aluminum grains. Also, when Al-5Ti-1B additions are made, nucleation frequently occurs above the equilibrium liquidus temperature. From a thermodynamic point of view, this phenomenon can occur only if regions of the melt (which contain borides and nucleate new grains) have a higher Ti concentration than is present in the bulk of the liquid. A mechanism has been proposed to account for this observation. When hyperperitectic additions of grain refiner were made, a metastable formation of Al solid was often observed to occur at 2 to 5 deg above the equilibrium peritectic temperature. Other researchers have made this observation and proposed that a metastable aluminide phase was formed, even though no X-ray evidence of this phase was found. The experiments reported here show that the metastable nucleation occurs on boride particles when cooling from high temperature, which allow high (metastable) quantities of dissolved Ti to be retained in portions of the melt.
- OSTI ID:
- 6311552
- Journal Information:
- Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 24:2; ISSN 0360-2133; ISSN MTTABN
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
ALUMINIUM ALLOYS
BORIDES
BORON
BORON ADDITIONS
BORON ALLOYS
BORON COMPOUNDS
DATA
DIAGRAMS
ELEMENTS
EXPERIMENTAL DATA
GRAIN BOUNDARIES
INFORMATION
METALLURGICAL EFFECTS
METALS
MICROSTRUCTURE
NUCLEATION
NUMERICAL DATA
PHASE DIAGRAMS
PHASE STUDIES
SEMIMETALS
THERMAL ANALYSIS
THERMODYNAMICS
TITANIUM
TITANIUM ALLOYS
TITANIUM BORIDES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS