Influence of the microstructure on the thermal conductivity of cast Al-Si-Cu-Mg alloys
Tutor / director / evaluatorSjölander, Emma
Document typeMaster thesis (pre-Bologna period)
Rights accessRestricted access - confidentiality agreement
Pure aluminium has a high thermal conductivity, but as alloying elements are added the thermal conductivity decreases. How much it occurs depends on the alloying elements and whether they are present in solid solution, as small precipitates or larger particles. The present work studies the influence of Cu and Mg additions on the thermal conductivity of Sr-modified as-cast and T6-heat treated Al-Si alloys for a wide range of temperatures (30-400 ºC). An unmodified Al-Si alloy with no additions was analysed as well so as to investigate the influence of the modification with Sr. Three properties were determined to calculate the thermal conductivity: thermal diffusivity, specific heat and density. Thermal diffusivity measurements were carried out by means of a Laser Flash device. Regarding the Sr-modified Al-Si alloys, the highest thermal conductivity corresponds to the alloy without the addition of other elements in both as-cast and T6 condition. The alloys containing Cu have in general a lower thermal conductivity than the alloys with solely Mg. The presence of Mg has an overall beneficial effect in as-cast conditions for an alloy containing Cu. In contrast, this addition becomes detrimental for a copper-bearing heat-treated alloy in most of the temperature range. With regard to the Sr-modification outcome, it was found that enhances thermal conductivity in as-cast alloys. Nevertheless, its influence after the heat treatment requires a further study. The thermal conductivity increases normally with the temperature and when the T6 heat treatment is applied. This increment is attributable to the purer aluminium matrix obtained as the precipitates form, grow and coarsen.
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