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Abstract
An extensive state of the art as regards the main productive variables relating to the premium products in AlSiCuMg is proffered in this dissertation. Two main domains of production improvement stand out: solidification and heat treatments.
Experimental techniques and suitable equipment were developed, enabling the study of solidification phenomena, solidification manipulation, and adequate heat treatment. The experiments´ assembly and their respective evolution are documented in detail.
The exploration of solidification phenomena was achieved by the construction of a quasi unidirectional furnace with data acquisition in 6 distinctive locations of the casting with an acquisition rate up to 10 Hz. A novel mathematical model was created to plot thermal maps, as well as gradient maps and cooling rates. It was also possible adequately to study the solidification fronts along the casting.
Another study was the solidification of the A354 alloy with the influence of a rotating magnetic field. In these experiments the mechanisms of grain refinement were analysed and new ones were proposed for a certain range of magnetic intensities and frequencies of rotation. The refinement of proeutectic alfa was achieved with success and mechanical properties were determined. In this study it was discovered that for the scoped magnetic intensities and frequencies there is a threshold that must be overcome, because despite the grain refinement, the mechanical properties are jeopardized. Much evidence was found of the strong influence of the rotating magnetic field on the distribution and quantity of secondary particles.
Another subject to be addressed was the development of a novel analysis technique for incipient melting. It was observed that despite the incipient melting reaction being detected in differential calorimetry, most of secondary particles do not cause porosity. This proof encourages possible optimizations on the duration of a multi-stage heat treatment. This thesis also expounds the method and resultant multi-stage heat treatment determined by differential calorimetry.
