Resumo:
Aluminum is the metal of modern life. Heat-treatable aluminum alloys currently occupy a
prominent place in the industrial sector and with even greater prospects for use in the future.
The A356 alloy is extended to automotive, aerospace and other industrial areas due to its
excellent properties, including high strength, low density and excellent castability. Aiming at
production cost benefits, less energy consumption and elimination of environmental damage
associated with the mining and refining sectors, the recycling of aluminum alloys has been
widely explored. In recycled foundry alloys, iron is the main impurity found and, due to its low
solubility in aluminum, its presence leads to the formation of second phases, such as β - Al5FeSi
intermetallic compounds which are presented in the form of thin and long platelets (needles )
which have a fragile character, degrading the strength and ductility of the alloy, as they act as
stress concentrators. The size of the β - Al5FeSi phase needles increases the higher the iron
content in the alloy and the lower the cooling rate. Thus, optimal control of iron concentration
in foundry alloys is essential. In order to evaluate the effect of iron content on the microstructure
and mechanical properties of the A356 alloy, the alloy was cast, containing 1% and 3% iron in
its composition and then heat treated. The microstructure after remelting and solidification
presents intermetallic phases with acicular morphology of the AlSiMgFe and AlFeSi
composition. On the other hand, the microstructure after heat treatment presents intermetallic
phases in needle shapes with β -Al5FeSi composition. The additions of iron resulted in a
decrease in the cooling rate. It was found that as the iron content increases, there is a reduction
in the distribution of the volume fraction of precipitates and an increase in grain size. It is also
verified that with different cooling rates, the volume fraction changes, concluding that the
higher the cooling rate, the greater the volume fraction. After performing the microhardness
test for post-remelting, it was possible to notice an increase in the values of alloys with iron
contents. The microhardness values in relation to the cooling rates used in quenching were
unexpected. The recycling simulation of this work and consequent iron contamination in the
A356 alloy generated changes in the solidification sequence, enabling the appearance of
primary phases formed of iron before the crystallization of aluminum grains.
