Al-Ti-C master alloys have a great potential as efficient grain refiners for aluminum and its alloys. In the present work, the Al-Ti-C master alloys are synthesized via a relatively novel technique through the reaction of a compacted mixture of K 2 TiF 6 and graphite with molten aluminum. The obtained alloys are examined using scanning electron microscopy (SEM), energy-dispersive spectroscopy, and X-ray diffraction (XRD) methods. The results indicate that the produced Al-Ti-C master alloys contain TiC and TiAl 3 particles within the aluminum matrix. Also, these alloys were evaluated using the KBI test mold. The results indicate that the produced Al-Ti-C master alloy is an efficient grain refiner for pure aluminum and its alloys compared with the Al-Ti-B one. The factors affecting the grain refinement of aluminum and its alloys are studied. The proper conditions for evaluating the efficiency of the produced Al-Ti-C master alloy to obtain a minimum grain size are as follows: temperature, 993 K (720°C); holding time, 2 minutes; and (Ti/Al) weight ratio, 0.01 pct.
Gas bubbles and electromagnetic forces (EMFs) in the electrolyte region of the aluminum reduction cells affect the flow pattern and hence the cell performance. Such performance is indicated by current efficiency. Dynamic simulation for the gas-induced flow in the aluminum reduction cell was performed using the Euler/Lagrange approach. The flow behavior and current efficiency in the cell are calculated due to different driving forces of gas bubbles, EMFs, and the combined effect of these driving forces. The gas bubbles-induced motion in the electrolyte (bath) layer was found more effective than the EMFs-induced motion. The bath velocity near the anode under various driving forces, bubble, EMFs, and the combined effect, was found to be 16.9, 5.8, and 25.2 cm/s, respectively, in the direction from the center of the anode to the projection of the anode, while the corresponding oppositely directed velocity near the cathode (just above the interface) was 3.8, 2.8, and 6.5 cm/s, respectively. The average current efficiencies calculated due to the previous driving forces were found to be 92.99, 95.04, and 94.62 pct, respectively.
Cavitation erosion resistance of steels is important in many applications. The investigation of such resistance, under different conditions, should be very useful. Cavitation erosion tests were carried out on carbon steel AISI-1045 using an ultrasonic induced cavitation facility. Cavitation erosion pits and their effect on the localized corrosion were investigated in detail in three different corrosive media: distilled water, tap water, and 3% NaCl water.
The results of the investigation using SEM indicated the formation of three types of pits on cavitating specimen surfaces: corrosion pits, erosion pits, and erosion-corrosion pits. The corrosion pits have different shapes, however, the lamellar structure is the dominant structure, and has a large size of about 100 μm. The erosion pits that were formed by the cavitation microjet impacts have sizes of a few micrometers. The erosion-corrosion pits were similar to the corrosion pits, except the erosion pits formed on the corrosion pit surface due to dissolution. The eroded surface removal was the largest in the case of saline water.
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