46
J. Karloopia et al.
response surface methodology has not as yet been broadly applied for the development of a statistical model and for predicting the response of welded joints
with specific respect to process parameters.
The objective of the present study was to effectively join the in-house fabricated
in situ 3 wt. pct. titanium diboride/12 Aluminium-Silicon composites (3 wt. pct
TiB 2 /12Al-Si) using the technique of friction stir welding. A mathematical model was
also developed for both optimizing and predicting the influence of process parameters
with high accuracy with the prime objective of obtaining a defect-free joint. An
overall improvement in the properties achieved by using friction stir welding of the
composites was made possible by an examination in a Field Emission Scanning
Electron Microscope (FESEM).
Experimental Procedures
Commercially available pure aluminum ingot and Al-20Si alloy ingot were used
as the initial raw materials for the fabrication of metal matrix composites. The
high-temperature electrically controlled muffle furnace was used to melt an ingot
of pure aluminum and the ingot of an Al-20Si alloy in a graphite crucible. The
weight percentage of silicon was reduced to 12%. Intermittent stirring was made
possible using a mechanically operated zirconium-coated stirrer. The entire procedure was conducted carefully so as to avoid the formation of secondary phases during
the casting operation, as reported in our earlier studies [18–20]. Titanium diboride
(TiB 2 ) phase was formed due to a reaction between the halide salts, i.e., potassium hexafluorotitanate (K 2 TiF 6 ), potassium tetrafluoroborate (KBF 4 ) and sodium
aluminium hexafluoride (Na 3 ALF 6 ) at 790 °C. The mixture of salts was divided into
four equivalent batches and was enclosed in an aluminium foil. The small batches
were then placed inside a low-temperature electric oven so as to remove the presence
of any moisture in the salts. An exothermic reaction between the salts results in the
formation and presence of the TiB 2 phase as shown below [10, 21, 22];
3K 2 TiF 6 + 13Al ⇔ 3Al 3 Ti + 3KAlF 4 + K 3 AlF 6
2KBF 4 + 6Al ⇔ 4AlB 2 + 2KAlF 4
Al 3 Ti + AlB 2 ⇔ TiB 2 + 4Al
The temperature plays a critical role during the reaction process and was kept well
below 800 °C. At higher temperatures, KBF 4 has the tendency to dissociate to form
potassium fluoride (KF) and boron trifluoride (BF 3 ) gas, which eventually results in
deficit of the element boron. A reaction time of 45 min was provided with intermittent
stirring. The final molten mixture was poured into a permanent mold of die steel and
J. Karloopia et al.
response surface methodology has not as yet been broadly applied for the development of a statistical model and for predicting the response of welded joints
with specific respect to process parameters.
The objective of the present study was to effectively join the in-house fabricated
in situ 3 wt. pct. titanium diboride/12 Aluminium-Silicon composites (3 wt. pct
TiB 2 /12Al-Si) using the technique of friction stir welding. A mathematical model was
also developed for both optimizing and predicting the influence of process parameters
with high accuracy with the prime objective of obtaining a defect-free joint. An
overall improvement in the properties achieved by using friction stir welding of the
composites was made possible by an examination in a Field Emission Scanning
Electron Microscope (FESEM).
Experimental Procedures
Commercially available pure aluminum ingot and Al-20Si alloy ingot were used
as the initial raw materials for the fabrication of metal matrix composites. The
high-temperature electrically controlled muffle furnace was used to melt an ingot
of pure aluminum and the ingot of an Al-20Si alloy in a graphite crucible. The
weight percentage of silicon was reduced to 12%. Intermittent stirring was made
possible using a mechanically operated zirconium-coated stirrer. The entire procedure was conducted carefully so as to avoid the formation of secondary phases during
the casting operation, as reported in our earlier studies [18–20]. Titanium diboride
(TiB 2 ) phase was formed due to a reaction between the halide salts, i.e., potassium hexafluorotitanate (K 2 TiF 6 ), potassium tetrafluoroborate (KBF 4 ) and sodium
aluminium hexafluoride (Na 3 ALF 6 ) at 790 °C. The mixture of salts was divided into
four equivalent batches and was enclosed in an aluminium foil. The small batches
were then placed inside a low-temperature electric oven so as to remove the presence
of any moisture in the salts. An exothermic reaction between the salts results in the
formation and presence of the TiB 2 phase as shown below [10, 21, 22];
3K 2 TiF 6 + 13Al ⇔ 3Al 3 Ti + 3KAlF 4 + K 3 AlF 6
2KBF 4 + 6Al ⇔ 4AlB 2 + 2KAlF 4
Al 3 Ti + AlB 2 ⇔ TiB 2 + 4Al
The temperature plays a critical role during the reaction process and was kept well
below 800 °C. At higher temperatures, KBF 4 has the tendency to dissociate to form
potassium fluoride (KF) and boron trifluoride (BF 3 ) gas, which eventually results in
deficit of the element boron. A reaction time of 45 min was provided with intermittent
stirring. The final molten mixture was poured into a permanent mold of die steel and