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Title: Grain refinement of A17Si shaped casting alloys
Author: Keeble, J. M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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An investigation was undertaken to clarify the effects of various grain refiners on primary grain size of A17Si type alloys. By observing the influence of master alloy grain refiners containing B, Ti, Ti and B, and Ti and C under controlled casting conditions (constant holding temperature of 750°C, cast into graphite moulds held at room temperature) with variations in holding time, addition levels and Ti:B ratios, it was possible to achieve a greater degree of understanding as to the required additions to attain desired refinement levels in the casting house. Two types of test were carried out. Firstly, two minute grain refiner tests, where the samples were taken from the melt two minutes after grain refiner addition. These tests were used to establish the effects of; increasing Si content from 0 to 7wt% (in the absence of grain refiner and with grain refiner additions of Al-Ti and A15Ti1B at a number of addition levels) and increasing addition level of Ti, B, Ti and B, and Ti and C on the primary grain size of A17Si. The second type of test established the influence on grain refinement, using additions of Ti, B, Ti and B, and Ti and C, of various holding times up to two hours. The effect on grain size of varying Ti:B ratio was also studied using master alloys containing both Ti and B with various ratios and also by making additions of Al-Ti and A1-B refiners. From the fade tests it has been found that, with additions of A1-Ti refiners, levels of Ti above the peritectic TiA13 level give best refinement with virtually no fade observed at any of the additional levels studied. For the two addition levels of AlTiC studied, grain size increases over holding time and decreases on stirring the melt after the two hour holding period, suggesting some nucleant particle settling. With Ti and B containing refiners, those with ratios of Ti to B < 2.2:1 produce finer primary grains sizes at given B levels with a reduced tendency to fade. Addition levels of 0.02wt%B or more produce finer grain sizes than lower addition levels due to increased numbers of nucleants, reducing observed effects of nucleant settling by ensuring sufficient B containing particles are in the melt to achieve adequate grain refinement even after a two hour holding period.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available