Comparison of thermodynamic databases for 3xx and 6xxx aluminum alloys

Abstract

Computational thermodynamics, or Calculation of Phase Diagram (CALPHAD) methods have proven useful in applications to modeling a variety of alloy properties. However, the methods are only as accurate as the thermodynamic databases they use, and two commercial thermodynamic databases exist for aluminum alloys: Thermotech and Computherm. In order to provide a critical comparison of these databases, we used both the databases to calculate equilibrium solid-state phase fractions and phase diagram isothermal sections of several industrial aluminum alloys: a 319-type and 356 cast alloys, as well as the wrought alloys 6022 and 6111. All of these alloys may be generically described as being based on the Al-Mg-Si-Cu quaternary with other additions such as Fe, Mn, and Zn. Although many of the results are consistent between the two databases, several qualitative and quantitative differences were observed. Many of these differences are found to be due to the intermetallic compounds involving Fe, Mn, Cr, and Zn. On the other hand, thermodynamics involving only phases from the Al-Mg-Si-Cu quaternary show good agreement between the databases, although some small differences still exist, particularly involving the quaternary Q phase. To understand and assess these differences, formation enthalpies and reaction energies from the databases were compared against density functional first-principles energetics. These comparisons indicate possible avenues for future improvements of Al-alloy thermodynamic databases. Finally, we demonstrate an interesting correlation between the calculated phase fractions and the measured yield strengths across this wide family of 3xx cast and 6xxx wrought alloys.

Thermodynamic Assessment of the Aluminum Corner of the Al-Fe-Mn-Si System

“…Moreover, neither of these two works gives any experimental evidence that a phase differing from Fe-bearing alpha-AlMnSi was observed. Ab-initio calculations, such as those performed by Ravi and Wolverton [23] in their comparison of available databases for aluminum alloys, could certainly be decisive in confirming the existence of such a quaternary phase. Unfortunately, such data are unavailable for the phases discussed here.…”

Anodisation of friction stir welds in AA 5052-O alloy

“…14 The Samples are produced when the revolution pitch is 0?02 (3000 rev min 21 , 50 mm min 21 ) and 0?03 mm rev 21 (3000 rev min 21 , 80 mm min 21 ), showing apparent grey strips on the anodised surface, as shown in Fig. 1.…”

Effect of iron addition on the crystal structure of the α-AlFeMnSi phase formed in the quaternary Al-Fe-Mn-Si system

“…Ravi and Wolverton [13] made a critical comparison of the two commercially available Al-alloy thermodynamic databases: Thermotech and Computherm. They observed some differences in the databases with regard to the intermetallic compounds involving iron, manganese, chromium, and zinc.…”