On the role of dissolution of the β-phase on the hardening and fracture characteristics of Al–2 wt% Mg

Abstract

Work‐hardening tests are made on the precipitating binary alloy Al–2 wt% Mg. The yield and fracture stresses and the fracture strain are determined for test samples in the form of circular wires differently pre‐annealed at relatively high temperatures to produce different grain sizes. The precipitation of the β‐phase is fully effected by proper heat treatment at the start of the test. Controlled dissolution of the precipitate is then made in steps and the corresponding stress‐strain relations recorde dat constant strain rate. The yield stress, fracture stress, and fracture strain show a somewhat parallel behaviour indicating a peak value at a particular time of dissolution at each dissolution temperature. This peak is found to shift towards lower times of dissolution as the dissolution temperature increases. Taking the position of the peak as indicative to a certain degree of dissolution, the activation energy characterizing the process is found to be (1.22 ± 0.1) eV comparable with the diffusion energy of magnesium atoms in the aluminium matrix. The dislocation slip distance, as calculated from the parabolic work‐hardening coefficient, is found to be minimum near the forementioned peak conditions. Testing the present results with the Cottrell‐Petch relations indicates that the fracture mechanism is not located at the grain boundaries.

Influence of Si concentration on the precipitation in Al-1at.% Mg alloy

“…The obtained value is in good agreement with that obtained by Dutta and Allen (33.1 kJ/mol) [21]. The migration energy of Si is calculated from the activation energy of Si diffusion in Al (124.0 kJ/mol) [22] and the formation energy of vacancies in Al (71.3 kJ/mol) [23]. By the same way as the diffusion energy of Mg in Al (125.2 kJ/mol) [22], the migration energy of Mg in Al can be determined.…”

Study of the developed precipitates in Al–0.63Mg–0.37Si–0.5Cu(wt.%) alloy by using DSC and TEM techniques

“…(i) Clustering of Si-Mg-vacancy: As has been treated elsewhere [16], the activation energy of clustering of Si-Mg-vacancy (53.0 kJ/mol) is approximately equal to the migration energy of Si in Al (52.7 kJ/mol) which is calculated from the activation energy of diffusion of Si in Al (124 kJ/mol) [26] and the formation energy of vacancies in Al (71.3 kJ/mol) [27]. On the other hand, the determined value of the activation energy of the clustering process is, also, very close to the migration energy of Mg atoms, 54 kJ/mol which is calculated from the activation energy of Mg diffusion in Al (125.2 kJ/mol) and the formation energy of vacancy [26].…”

STUDY OF PRECIPITATION KINETICS OF AN Al-Mg-Si ALLOY USING DIFFERENTIAL SCANNING CALORIMETRY

“…where α is the heating rate, Tp is the temperature of the peak maximum, and R is the gas constant (8.314 J mol -1 K -1 ). From the quenched alloy results, the activation energy for the first peak (GP zones) is about 66.894 KJ/mol which is much smaller than the ones for diffusion of silicon and magnesium in aluminum and very close to the one for vacancy migration (71.3 KJ/mol) [15]. This reaction can be explained in terms of vacancy cluster formation.…”