Analysis of aluminium based alloys

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Analysis of aluminium based alloys by calorimetry:quantitative analysis of reactions and reaction kinetics

M.J.Starink*

Differential scanning calorimetry(DSC)and isothermal calorimetry have been applied extensively to the analysis of light metals,especially Al based alloys.Isothermal calorimetry and differential scanning calorimetry are used for analysis of solid state reactions,such as precipitation, homogenisation,devitrivication and recrystallisation;and solid–liquid reactions,such as incipient melting and solidification,are studied by differential scanning calorimetry.In producing repeatable calorimetry data on Al alloys,sample preparation,reproducibility and baseline drift need to be considered in detail.Calorimetry can be used effectively to study the different solid state reactions and solid–liquid reactions that occur during the main processing steps of Al based alloys(solidification,homogenisation,precipitation).Also,devitrivication of amorphous and ultrafine grained Al based powders and flakes can be studied effectively.Quantitative analysis of the kinetics of reactions is assessed through reviewing the interrelation between activation energy analysis methods,equivalent time approaches,impingement parameter approaches,mean field models for precipitation,the Johnson–Mehl–Avrami–Kolmogorov model,as well as novel models which have not yet found application in calorimetry.Differential scanning calorimetry has occasionally been used in attempts to measure the volume fractions of phases present in Al based alloys,and attempts at determining volume fractions of intermetallic phases in commercial alloys and amounts of devitrified phase in glasses are reviewed.The requirements for the validity of these quantitative applications are also reviewed.

Keywords:Differential scanning calorimetry,Precipitation,Aluminium,Modelling,Transformation IMR/419

Introduction

Calorimetry is an analysis technique that is part of a group of techniques collectively known as thermal analysis methods.In its broadest sense,thermal analysis refers to the measurement of changes in properties of substances under a controlled temperature program. Thermal analysis techniques can be classified according to the type of temperature program that the sample is subjected to and the measured(output)signal.The most commonly used temperature programs are either iso-thermal hold or heating(scanning)at constant rate, while more recently,temperature modulated scanning and reaction controlled heating have also found application.The signals measured in thermal analysis can include heatflows,temperature changes,mass, evolved gasses,length changes,elastic modulus,and many other properties that characterise properties or reactions of interest.Calorimetry refers to thermal analysis methods that measure the heat evolution from a sample under a controlled temperature program. The two most often applied calorimetry techniques are isothermal calorimetry and differential scanning calorimetry(DSC),which,as the name suggests,is by definition non-isothermal(i.e.a temperature scan). Apart from the more common applications to polymers,glasses and pharmaceuticals,calorimetry has also been applied extensively to the analysis of light metals;especially Al based alloys,but also Ti and Mg based alloys.For light metals for structural applications, DSC is used mostly for analysis of solid–solid reactions, including precipitation,dissolution and recrystallisation, for determining temperatures of incipient melting,and for solidification studies.The present paper presents a review of the techniques and analysis methods of isothermal calorimetry and DSC that are relevant to the study of Al based alloys.The aim is to bring together and critically review the published work that is of direct use to researchers working in thefield of calorimetry of light metals.The focus is mostly on work published in the past10years.

Aluminium based alloys studied by calorimetry can broadly be divided into three groups.The most often

*Materials Research Group,School of Engineering Sciences,University of

Southampton,Southampton S0171BJ,email m.j.starink@soton.ac.uk

ß2004IoM Communications Ltd and ASM International

Published by Maney for the Institute of Materials,Minerals and Mining

and ASM International

DOI10.1179/095066004225010532International Materials Reviews2004VOL49NO3–4191

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