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