Demonstration Experiments on Grain Refinement Caused by Vibration Mold Using Ammonium Chloride Solution

For the purpose of understanding the mechanism of grain refinement in cast metal by mechanical vibration, demonstration tests were conducted using an ammonium chloride solution. Ammonium chloride solution and molds with various shape were prepared for the water model experiment. In the case of an open mold, ammonium chloride crystals crystallized on the mold wall and grew toward the center of the mold without vibration. However, when vibration was applied, countless crystals generated at the upper side of the solution immediately after pouring. In the case of a full plugged mold, no wave and convection occurred in the solution even when vibration was added, and the behavior seen was similar to the case without vibration. When only convection occurred in the full plugged mold, crystals were found to move from the mold wall into the solution. When a weir was set in the riser, it helped prevent the generation of crystals on the mold wall of the riser from migrating to the specimen. When a mold with a weir was used for Al-2%Cu alloy, crystals in the specimen did not become refined as seen in the water model experiments.These results demonstrate that a large amount of crystals are generated at the boundary between the surface of the molten metal and mold wall when molten metal is vibrated, and these fine crystals fill into the mold due to sedimentation or convection, thereby achieving grain refinement. [doi:10.2320/matertrans.F-M2023804]