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MTDATA Demonstration : Light Metal Alloys

Contents

  1. Introduction
  2. The Al-Si binary phase diagram
  3. The Al-Si-Zn system
  4. MULTIPHASE calculations

Introduction

Light metal alloys are used for a wide range of applications, including aerospace engineering, structural equipment, turbo-jet engines, transport and marine engineering. For these applications a variety of mechanical and physical properties are required. The properties of alloys are dependent on their phase constitution under specific environmental conditions. A knowledge of the phase constitution is therefore fundamental to the development of new and improved alloys, and to their manufacture into marketable products and their end usage.

Commercial alloys contain many alloying elements making the possible variations in phase constitution almost infinite. Published phase equilibrium data for ternary and higher-order light metal systems are scarce, and the experimental investigation of complex alloys is usually prohibitively expensive.

MTDATA, together with its associated databases, provides an alternative approach by means of which the phase constitution of complex multicomponent alloys can be calculated relatively inexpensively.


The Al-Si binary phase diagram

Many light metal alloys are based on the aluminium-silicon system. The Module ACCESS allows the thermodynamic data for this system to be extracted from a database and stored in a data file, while the Module BINARY enables the binary phase diagram to be calculated.

WHICH MODULE ? access
ACCESS OPTION ? define system 'Al,Si' source sgte_sol !
SEARCHING FOR SYSTEM Al,Si
sgte_sol - SGTE Solution Database 3.01 - 19/7/93
ACCESS OPTION ? save
ACCESS OPTION ? return
WHICH MODULE ? binary
BINARY OPTION ? define data !
BINARY OPTION ? step temperature 500 1800 10 !
BINARY OPTION ? compute !

The REPLOT command of BINARY allows the enlargement of portions of the calculated diagram, providing more detail, here of the eutectic in the aluminium-silicon system. The REPLOT command also allows experimental data to be superimposed.

BINARY OPTION ? ordinate limits 600 1000 !
BINARY OPTION ? abscissa limits 0 0.14 !
BINARY OPTION ? replot experimental_file 'alsi.exp' go

The thermodynamic data employed, which form the basis for multicomponent calculations, have been computer-optimised to take into account the experimental phase equilibria shown, and also the experimentally determined thermodynamic properties.


The Al-Si-Zn system

Zinc is added as a deliberate alloying element to aluminium-silicon based alloys, and is also used as a corrosion resistant coating on alloys for various applications. In both cases a knowledge of the melting temperatures, that is of liquidus temperatures, is particularly important, for example for joining technology.

The Module TERNARY allows the calculation of ternary systems, here for the aluminium-silicon-zinc system. Phase labels may be added by means of a cursor.

WHICH MODULE ? ternary
TERNARY OPTION ? define system 'Al,Si,Zn' source sgte_sol output 'alsizn' !
SEARCHING FOR SYSTEM Al,Si,Zn
sgte_sol - SGTE Solution Database 3.01 - 19/7/93
TERNARY OPTION ? set temperature 825 ! compute !

Within TERNARY the command REPLOT allows magnification of chosen portions of the ternary system, here for example, the aluminium-rich corner.

TERNARY OPTION ? set n(1) 0.82 n(2) 0.10 n(3) 0.08 !
TERNARY OPTION ? replot magnification 2.25 2.25 !

Liquidus projections

The liquidus projection for this ternary system can be calculated using MTDATA's generalised liquidus projection application.

WHICH MODULE ? application
APPLICATION OPTION ? define datafile 'alsizn' !
APPLICATION OPTION ? set 'Al' 1.0 0.0 0.0 !
APPLICATION OPTION ? set 'Si' 0.0 1.0 0.0 !
APPLICATION OPTION ? set 'Zn' 0.0 0.0 1.0 !
APPLICATION OPTION ? range t 2000 300 0.1 !
APPLICATION OPTION ? 'mt-liqsect.mac
Enter number of steps ?
: 50
Orientation of the diagram ?
: 'Al'
: 'Si'
: 'Zn'
Labelling option ?
: 0
Plotting option ?
: 0
Contour step ?
: 50
Root of results file name ?
: 'alsizn'
APPLICATION OPTION ? compute !

The liquidus projection application can also be used to magnify part of the diagram for the whole ternary system, showing more detail of the liquidus in the vicinity of the aluminium-rich corner of the system.

APPLICATION OPTION ? set 'A' 1.0 0.0 0.0 !
APPLICATION OPTION ? set 'B' 0.6 0.4 0.0 !
APPLICATION OPTION ? set 'C' 0.6 0.0 0.4 !
APPLICATION OPTION ? range t 2000 300 0.1 !
APPLICATION OPTION ? 'mt-liqsect.mac
Enter number of steps ?
: 50
Orientation of the diagram ?
: 'A'
: 'B'
: 'C'
Labelling option ?
: 0
Plotting option ?
: 0
Contour step ?
: 50
Root of results file name ?
: 'alsizn1'
APPLICATION OPTION ? compute !

This combination of phase diagrams relating to aluminium-rich Al-Si-Zn alloys provides detailed information on the melting/solidification temperatures, crystallisation paths, and a knowledge of the various coexisting phases stable under conditions of temperature and composition. The data have been successfully used to assist the development of brazing technology.


MULTIPHASE calculations

Even relatively simple aluminium-based alloys are surprisingly complex, and the types and amounts of phases present as precipitates can vary widely as a function of allowable composition variation within the specification. Such variations can lead to quite deleterious results and require control.

The Module MULTIPHASE allows the calculation of the proportions of phases present as a function of temperature, here for an aluminium - 1 wt % iron, 1 wt % silicon alloy.

WHICH MODULE ? multiphase
MULTIPHASE OPTION ? define system 'Al,Fe,Si' source sgte_sol !
SEARCHING FOR SYSTEM Al,Fe,Si
sgte_sol - SGTE Solution Database 3.01 - 19/7/93
MULTIPHASE OPTION ? set w(1) 0.98 w(2) 0.01 w(3) 0.01 !
MULTIPHASE OPTION ? step t 750 950 2.5 !
MULTIPHASE OPTION ? compute print graphics !
MULTIPHASE OPTION ? ordinate mass phase !
MULTIPHASE OPTION ? plot go

The proportions of the liquid phase and the fcc aluminium-rich phase are given on cooling, the diagram shows the precipitation of compound phases on further cooling, primarily Al5FeSi.

More detail can be provided by setting the ordinate limits, to show the proportions of the compound phases as a function of temperature, and providing a knowledge of the solidification process that would be extremely difficult and expensive to determine experimentally.

MULTIPHASE OPTION ? ordinate limits 0 0.1 !
MULTIPHASE OPTION ? plot go

The plotting options within MULTIPHASE are varied to suit different requirements.

N_(AMOUNT)
MASS
X_(MOLE FRACTION)
W_(WEIGHT FRACTION)
CHEMICAL_POTENTIAL
MOLALITY
PRESSURE
VOLUME
ACTIVITY_(NOTIONAL)
COMPONENT_DISTRIB.
LOG_SCALE
LIMITS
FOCUS_ON_COMPONENT
COMPONENT_ACTIVITY
GIBBS_ENERGY
ENTHALPY
ENTROPY
HEAT_CAPACITY
PARTIAL_PRESSURE
TEMPERATURE
USER_VARIABLE

The following shows the proportion of iron and silicon present in the fcc phase as a function of temperature.

MULTIPHASE OPTION ? ordinate component_distrib mass_in_phase(fcc) !
MULTIPHASE OPTION ? ordinate limits 0 0.01 ! plot go

The above examples of phase equilibria illustrate just a few applications of MTDATA in relation to aluminium alloy systems. Utilisation of the various databases within MTDATA allows the calculation of phase equilibria for a huge range of commercially important alloys. The areas cover alloy development, energy conversion, extractive metallurgy, crystal growth, joining (solders, welding, brazing), waste processing and recycling, and materials handling and compatibility. The benefits include cost and time saving, process prediction, improved control of processes and pollution and corrosion control.


 

Updated 28 April 2010