220
S. Mozammil et al.
are K 2 TiF 6 and KBF 4 . One salt has titanium in it while the other salt has boron in it.
The two salts were carefully added to the molten aluminum-copper alloy. Here, both
time step and a temperature control unit were equipped with the stir casting setup
with the primary intent of controlling the reaction time and temperature. A stirrer
made of stainless steel was used to prevent the possibility of contamination of the
molten metal (alloy) during fabrication of the composite. Upon careful addition of
the two salts to the molten aluminum–copper alloy, the reaction becomes vigorous
and primarily exothermic in nature resulting in the formation and presence of the
TiB 2 phase along with slag or dross. The slag that is formed is essentially rich in the
compound KAlF 4 and can be easily separated from the liquid metal. This technique
or approach is often referred to as the mixed salt route.
Al − Cu + K 2 TiF 6 + KBF 4 → Al + TiB 2 + Al 2 Cu + KAlF 4
The entire operation for fabricating the in situ composites depends on four primary
process parameters. These are essentially the following:
(1) Temperature during reaction,
(2) Duration of reaction,
(3) Cryolite effect, and
(4) Ratio of Ti: B.
For fabrication of the Al-4.5%Cu-xTiB 2 composite, the required reaction temperature was 750°C and the reaction time was 40 min. The operation was not carried
out at a higher temperature primarily because at the higher temperature, say around
800°C, the salt KBF 4 has a tendency to dissociate to form KF along with BF 3 gas,
which can easily escape from the crucible resulting in a gradual loss in the boron
content. The influence of reaction time is also important primarily because in order to
complete the reaction it does require some time. An insufficient reaction time will not
allow the reaction to be complete and the unreacted salt that is left out from the liquid
metal will find its way into the dross, which often results in a loss of both titanium
(Ti) and boron (B). The ratio of titanium and boron must be kept at 2.2:1. With an
extra quantity of titanium, the chances for the formation of the Al 3 Ti are enhanced.
However, with an excess amount of Boron, the chances for the formation of AlB 2 are
favored. To stabilize the reaction, 10-gram cryolite was added to the molten solution.
The whole melting process was carried out under a flux cover (50% KF: 50% NaF)
so as to facilitate removal of the oxide film from the melt surface while concurrently
acting as a protective layer for the absorption of gas. The dissolved hydrogen gas in
the melt was removed by using the degasser (C 2 Cl 6 ). In order to get required shape
of the casting, the molten slurry was gently poured into a die steel mold cavity. The
composition of pure aluminum (Al) and copper (Cu) is summarized in Table 1.
S. Mozammil et al.
are K 2 TiF 6 and KBF 4 . One salt has titanium in it while the other salt has boron in it.
The two salts were carefully added to the molten aluminum-copper alloy. Here, both
time step and a temperature control unit were equipped with the stir casting setup
with the primary intent of controlling the reaction time and temperature. A stirrer
made of stainless steel was used to prevent the possibility of contamination of the
molten metal (alloy) during fabrication of the composite. Upon careful addition of
the two salts to the molten aluminum–copper alloy, the reaction becomes vigorous
and primarily exothermic in nature resulting in the formation and presence of the
TiB 2 phase along with slag or dross. The slag that is formed is essentially rich in the
compound KAlF 4 and can be easily separated from the liquid metal. This technique
or approach is often referred to as the mixed salt route.
Al − Cu + K 2 TiF 6 + KBF 4 → Al + TiB 2 + Al 2 Cu + KAlF 4
The entire operation for fabricating the in situ composites depends on four primary
process parameters. These are essentially the following:
(1) Temperature during reaction,
(2) Duration of reaction,
(3) Cryolite effect, and
(4) Ratio of Ti: B.
For fabrication of the Al-4.5%Cu-xTiB 2 composite, the required reaction temperature was 750°C and the reaction time was 40 min. The operation was not carried
out at a higher temperature primarily because at the higher temperature, say around
800°C, the salt KBF 4 has a tendency to dissociate to form KF along with BF 3 gas,
which can easily escape from the crucible resulting in a gradual loss in the boron
content. The influence of reaction time is also important primarily because in order to
complete the reaction it does require some time. An insufficient reaction time will not
allow the reaction to be complete and the unreacted salt that is left out from the liquid
metal will find its way into the dross, which often results in a loss of both titanium
(Ti) and boron (B). The ratio of titanium and boron must be kept at 2.2:1. With an
extra quantity of titanium, the chances for the formation of the Al 3 Ti are enhanced.
However, with an excess amount of Boron, the chances for the formation of AlB 2 are
favored. To stabilize the reaction, 10-gram cryolite was added to the molten solution.
The whole melting process was carried out under a flux cover (50% KF: 50% NaF)
so as to facilitate removal of the oxide film from the melt surface while concurrently
acting as a protective layer for the absorption of gas. The dissolved hydrogen gas in
the melt was removed by using the degasser (C 2 Cl 6 ). In order to get required shape
of the casting, the molten slurry was gently poured into a die steel mold cavity. The
composition of pure aluminum (Al) and copper (Cu) is summarized in Table 1.