INFLUENCE OF METHODS FOR ALTI MASTER ALLOY PRODUCTION ON ITS STRUCTURE AND EFFICIENCY IN ALUMINUM ALLOY MODIFICATION

Abstract

A comparative study on the effect of methods for obtaining AlTi4 modifying master alloys on the sizes of Al3Ti intermetallics is made. It is found that increasing cooling rates at solidification from 10–15 °C/s (crystallization in a hot cast iron mold, a plate 30 mm in thickness) to 60–65 °C/s (crystallization in a cold cast iron chill mold, a rod 20 mm in diameter, 170 mm in length) reduces the length and thickness of needle-shaped intermetallics almost twice (397×23 to 215×13 μm). At the same time, lower electrical conductivity and higher alloy density in a solid state are observed. Melt modification with 0,5 wt.% magnesium addition causes the formation of homogeneous 98×3 μm fine-needle intermetallics. The addition of magnesium slightly reduces electrical conductivity and density compared with the AlTi4 master alloy crystallized at the same cooling rate (60–65 °C/s). Modification of A97 grade aluminum and AK9ch alloy (Al–Si–Mg system) with the specified master alloys at the same amount of titanium added (0,01 wt.%) exerts hereditary influence on the density and electrical conductivity, and macrograin (A97) and dendrites of aluminium (AK9ch). The maximum modifying effect is provided by the AlTi4 master alloy containing 0,5 wt.% magnesium. When introduced into the alloy, it contributes to the formation of 10 μm aluminum dendrites 1427 pcs/mm2 in total in the alloy structure. When the AK9ch alloy is modified with the master alloy crystallized at cooling rates of 10–15 °C/s, 28 μm dendrites 672 pcs/mm2 in total are formed in the alloy structure. It is suggested to use density and electrical conductivity determination methods for express evaluation of master alloy modifying effectiveness.