MODIFYING ALUMINUM WHEN CASTING INGOTS WITH MASTER ALLOY RODS

摘要

Hotshortness is a technological property and determines the tendency of metals and alloys toward brittle intercrystallite fracture in the presence of a liquid phase along the grain boundaries [1]. Despite the high plasticity, technical aluminum has a high tendency toward formation of hot cracks. When casting rectangular large ingots, they usually form on their bottom part or on the bottom part with a shift to the wide side. This was connected with the lack of synchronization in the crystallization of the outside and inside area of an ingot and with varying rates of subsequent cooling. This inevitably leads to shrinkage problems at the start of the peripheral layers, and then inside - this also causes cracks to appear. One method of eliminating hot cracks is by grinding grains and eliminating the columnar structure by introducing modifiers to the melt [1]. The work was conducted on rectangular ingots, 400x1560 mm, 2500 mm high, weighing 5.5 tons, cast from technical aluminum grade A7. Simultaneously the same continuous casting machine was used to cast (casting temperature 700-710 deg C) two ingots from the same metal, employing flat pans.. The aluminum was modified with rod master alloys (8.0 mm diameter), prepared from AI-TiCNO (titanium hydroxycarbonitride) and Ai-TiN (titanium nitride).