COST 507 - Repositório Aberto da Universidade do Porto

at least 95% by Fe, possibly 99%, although the pure Fe cubic analogue is (probably)
not truly stable in the Al-Fe-Si system, at least at temperatures close to where the
compound is formed from the melt. In the quaternary system, Fe will mix with Mn on
the second sublattice.
The hexagonal beta phase, of approximate composition Al| 0 Mn 3 Si, is formed at high
Mn and low Si levels. This also exists with a range of Si composition, and we are
currently modelling this phase with the sublattice description
Al, 5 Mn 6 Si(Al,Si) 4
There is no evidence of any appreciable solubility of silicon in Al 6 Mn or ALMn and
these phases have taken to be stoichiometric binary compounds in this ternary system.
4 Thermodynamic Data
The only thermodynamic data available during the period in which the assessment was
carried out were some Cp measurements for the cubic-alpha phase and the enthalpy of
transformation of a cubic-alpha phase to beta plus liquid, all derived from DTA
measurements [90Rea7Tib, 96Tib]. However, a preliminary value for the enthalpy of
formation of a sample of the C alpha phase has just become available [97Leg], but has
not yet been incorporated into the assessment, since further enthalpy data are likely to
emerge from the same source.
5 Optimisation.
A considerable effort has been expended in the optimisation of the phase diagram
information for this system, but with the uncertainty in the phase equilibria noted
above, the current assessment can still only be regarded as preliminary. The revision
of data for the Al-Mn binary system of Jansson and Chart [97Jan/Cha] has been
incorporated.
In the current optimisation, the highest weighting has been placed on the latest results
for the 4 wt% Si isopleth due primarily to Thornton [96Tho] (see Fig 1) and the
primary phase crystallising from a liquid containing 6 wt% Mn, 4 wt% Si was taken
to be cubic-alpha [96Sim] and not beta, as suggested by [51Pra/Ray]. The data of
Zakharov et al [88Zak/Gul] have also been included, together with the information
from Redford et al [90Red/Tib] and [94Kol7Sig].
6 Results
The calculated co-ordinates of the four invariant points are compared to the literature
values (mostly based solely on those of [43Phi]) in Table 1.
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