COST 507 - Repositório Aberto da Universidade do Porto

Smith Thermal Analysis Studies of Al-rich regions
of the Al-Mn, Al-Mn-Fe and Al-Mn-Si Systems
UKI
J.A.J.Robinson*, F.H.Hayes, A.Semeels** F.Weitzer*** and P.Rogl***
Manchester Materials Science Centre, University of Manchester & UMIST, UK
*present address: National Physical Laboratory, Teddington, Middlesex, UK.
**Dept. Metaalkunde en Toegepaste Materiaalkunde, KUL, Leuven, Belgium.
*** Institut für Physikalische Chemie der Universität Wien, Vienna, Austria.
Abstract
Smith thermal analysis measurements carried out in Manchester during COST 507-11
(Round 2) on selected Al-rich alloys in the Al-Mn, Al-Mn-Si and Al-Fe-Mn systems
are reported. Phase boundary and invariant reaction temperatures are given for Al-Mn-
Si alloys containing 4wt% Si, 0-6 wt% Mn, for Al-Fe-Mn alloys containing 2 wt%
Mn, 0-3 wt% Fe, carried out in collaboration with Group Bl (KUL.Leuven), and for
selected Al-Mn binary and Al-Fe-Mn ternary alloys, carried out in collaboration with
Group Al (University of Vienna). Liquidus temperatures for the Al-Mn-Si and Al-Fe-
Mn alloys are found to be higher than reported by Philips [43Phi]. Results for the Al-
Mn binary system agree well with the data presented by McAlister and Murray
[87McA] although not all of these are for stable equilibria.
1 Introduction
During the COST 507-11 Action it became evident that new and additional phase
diagram measurements were needed to resolve questions arising from Al-Fe-Mg-Mn-Si
assessment programme. The Smith method of thermal analysis [40Smi], successfully
used previously in Manchester to study phase boundaries and invariant reactions for a
variety of low melting Au, Ag, In and Al-alloy systems [92Hor, 94Hayl&2].
2 Smith Thermal Analysis
Smith thermal analysis, originally proposed mainly as a calorimertric method for
determining heat capacities and latent heats [40Smi], differs from conventional
differential thermal analysis, DTA in a number of ways. In the Smith method, the
temperature difference between the sample and the furnace wall is maintained at a preselected
value. Thus in the Smith method the heating or cooling rate is not controlled
directly. Maintaining a constant temperature difference between the sample and the
heat source/sink creates a condition of constant rate of heat transfer to/from the
sample. Over temperature ranges where the sample lies in a single phase region or in a
two-or three-phase region where the phase fractions and compositions remain constant,
the effective heat capacity of the sample also remains constant, resulting in a constant
rate of change of temperature with time, i.e dT/dt = constant. When the sample reaches
a phase boundary or invariant reaction temperature on heating or cooling there is an
abrupt change in the effective heat capacity which gives a corresponding immediate
change in dT/dt. This effect is very sensitive and forms the basis of the Smith method
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