Precipitation Kinetics of an Al-15% Mg Alloy Studied by Microcalorimetry and TEM

Abstract

The kinetics of β′ formation from supersaturated Al-15mass%Mg solid solutions was studied by microcalorimetry and transmission electron microscopy (TEM). It is shown that the transformation can not be described by the commonly used equation:The function f(α) is different at different temperatures. Apparent activation energies decrease with amount transformed from 1.07 eV to 0.7 eV. These findings are discussed in terms of overlapping of the nucleation and growth processes for β′. IntroductionAlthough different symbols for the zones and phases have been used, most work on the precipitation in Al-Mg [1,2,3,4] [4,7], it is the main hardening precipitate [8], and β is the equilibrium phase (approximate composition Al 3 Mg 2 ) having an FCC structure with a = 2.824 nm [4,7]. When solid solutions with up to 17 mass%Mg are aged at temperatures in excess of about 110°C no L1 2 ordered structures or zones form. In solid-quenched and liquid-quenched Al-Mg aged between about 110°C and 250°C the β′ phase forms first and the β phase only appears in the later stages of ageing when the Mg depletion of the matrix is nearly completed [4,9].In the present work the kinetics of precipitation in an Al-15mass%Mg alloy was studied by TEM and microcalorimetry. The latter technique allows the determination of the progress of the reaction at constant temperature with a very high precision. ExperimentalA high purity alloy with nominal composition Al-15Mg was produced by conventional casting and subsequent rolling at Centre de Recherches de Voreppe (Aluminium Pechiney). Chemical analysis revealed the composition 14.5 ± 0.2 mass % Mg (corresponding to 15.8 at %), with typical total impurity content about 0.03 mass % (mainly Si). The grain size is very large: about 1 to 2 mm.

Role of magnesium and minor zirconium on the wear behavior of 5xxx series aluminum alloys under different environments

“…The wear rate of the alloys in dry sliding condition is found to decrease with the increased hardness of the alloys and this result is found to be consistent with the Archard's theory (Fig. 4) [29].…”

Thermal stability of Al–Mg alloys after solidification under high pressures

“…For example, the precipitation sequence in the Al(Mg) solid solution prepared by solution treatment was found as follows [1][2][3][4][5][6][7][8]:…”

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“…For the purpose of the present paper, data on a number of reactions have been considered: isothermal calorimetry data on precipitation of β' at 180ºC on an air-cooled Al-16at%Mg alloy, isothermal calorimetry data precipitation of the L1 2 ordered phase in air-cooled Al-16at%Mg at 80 and 85°C, precipitation of the L1 2 ordered phase in water quenched Al-Li and isothermal calorimetry data on precipitation of the Si phase in an air cooled Al-6at%Si alloy (for experimental details see [52]). In line with previous publications [21][22][23][24][25][26][27] this new data could be fitted well by Eq.…”