Abstract:
The current work emphasizes establishment of relationship between microstructure and cold
deformation behavior of aluminum-copper -magnesium alloys. Aluminum-coppermagnesium
alloys with varying Cu% and Mg% were casted and undergone cold deformation
after homogenization, and their microstructures were examined using optical microscope.
Using CALPHAD method, phases developed for different levels of Cu and Mg were modeled
in JMatPro software package. It has been found that the prediction performed in equilibrium
condition matches closely to phase fraction simulation. It can predict several extra phases in
comparison to the equilibrium simulation. Image analysis by ImageJ also confirms this
finding experimentally. Finally, the effects of deformation were studied by measuring the
hardness of those alloys.
From this study it was possible to predict the weight fractions of phases formed during
solidification and homogenization using CALPHAD modeling. EDX results confirmed the
formation of Al2Cu phase (white phase) and Al7Cu2M and Mg2Si phases (black phases) as
modeled in CALPHAD. With increasing amount of copper and magnesium in the binary
aluminum-copper alloy system, fraction of Al2Cu, Al7Cu2M, Al2CuMg and Mg2Si phases
increased which increased hardness values. However, those additions lowered liquidus and
solidus temperatures of alloys as investigated from DTA and modeling.
The phase fractions of different alloys obtained from CALPHAD were verified using image
analysis techniques. Image analysis data showed a convincing conformation of phases that
formed during solidification and through solid state diffusion.
Homogenization and solution treatment had a negative effect on the hardness values of
investigated aluminum alloys due to dissolution of Al2Cu and Mg2Si phases in to the
aluminum matrix. On the other hand, deformation increased the number of dislocations by
interactions of dislocation during deformation and other defects, which caused an
enhancement of hardness values. Deformation also causes microstructural changes by destroying the necklace like shape of Al-Cu-Mg phases initially obtained in as-cast and
homogenized alloys. For this reason, with larger amount of deformation, the increment of
hardness may not be very significant. After comparing the effects of all the processing
parameters i.e. homogenization, deformation and alloy addition on hardness, it was revealed
using ANOVA modeling, that magnesium addition and amount of deformation affects
hardness of Al-Cu-Mg alloys to a large extent compared to addition of copper and
homogenization.
