STUDIES ON GRAIN REFINEMENT OF ALUMINUM ALLOYS
Keywords:
Grain refinement, Master alloys, Alcan test, Undercooling, TiAl3 phase, Growth restricting factor (GRF)Abstract
Grain structure is an important and readily observable feature in aluminum alloy castings. Depending on the constitutional and heat-flow conditions in a solidified Al alloy, various morphologies are possible. Grain refining is one of the predominant techniques in controlling the quality of castings. It plays a vital role in improving metallurgical characteristics and mechanical properties of Al alloys. Fine equiaxed grains ensure remarkable benefits. There are a number of techniques to achieve fine equiaxed grain structure, but grain refinement by the addition of grain refiners referred to as grain refinement / inoculation is the most popular due to its simplicity. Grain refinement has been studied extensively by researchers for several decades, not only for developing efficient grain refiners but also for achieving an understanding of the mechanism of grain refinement. In spite of its commercial importance, benefits and numerous scientific studies in this area, the grain refinement of Al and its alloys is still a controversial subject. Solute elements like titanium segregate to the inoculants/melt interface affecting the dendrites and also affect the constitutional undercooling at the solid–liquid interface. This segregating power of an element is quantified by the growth restricting factor (GRF). In this paper, various aspects covering the wide spectrum of grain refinement has been presented for several Al alloy systems. A comparison of commercially available grain refiner’s performance has been presented. Also fabrication of grain refiners and their morphological effects on grain refinement has been discussed. Further an attempt has been made to explain the mechanism of grain refinement.
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