Avaliação estrutural da liga AlSi7MgMn fundida utilizando cavacos de usinagem briquetados como matéria-prima

Abstract

This course completion work (TCC) aims to evaluate the microstructure of an ingot of AlSi7MgMn (or A356) alloy by casting in permanent mold and graphite mold from compacted and centrifuged chip briquettes of this alloy. With this, to evaluate the metallurgical quality of the material produced by melting and to assess the quality of this raw material for the foundry industry. The conception of this work arose from the professional internship carried out at company X, which performs the briquetting of residual chips, from a machining and aluminum line, in order to increase the added value of the scrap. However, the chips are impregnated with soluble oil, of mineral origin, during the process. In this sense, the objective of the work was to investigate the possible contamination of organic material and Iron in the recycled casting through microstructural analysis of ingots fused using only the briquetted chips as raw material. Thermodynamic calculations using the CALPHAD method as well as optical and scanning electron microscopy (SEM) techniques of the remelted and contaminated material were used for this analysis. It was observed, that both the ingots, cast in permanent steel and graphite molds, showed high porosity. A large amount of dark smoke was released during melting of the briquettes, indicating that the high porosity is due to the hydrogen porosity phenomenon caused by the presence of mainly impregnated organic material. In addition, the presence of intermetallics of the type α- Al(Fe,Mn)Si and β-AlFeSi suggest Iron contamination during the industrial process of company X. Thus, the research conducted suggests that the briquettes should be thermally pretreated, in order to pyrolyze all existing hydrocarbons, before being sold as scrap. In addition, it is extremely important to use dry, moisture-free casting equipment, reducing the porosity caused by hydrogen as much as possible. Regarding Fe contamination, it was not possible to determine the final composition of the casting, but the Mn content of the alloy was not sufficient to suppress the complete formation of the β-AlFeSi phase, which was formed in a small amount and which can be detrimental to the mechanical properties of the alloy.