Kinetics of natural aging in Al-Mg-Si alloys studied by positron annihilation lifetime spectroscopy

Abstract

The process of natural ageing in pure ternary Al-Mg-Si alloys was studied by positron annihilation lifetime spectroscopy in real time in order to clarify the sequence and kinetics of clustering and precipitation. It was found that natural ageing take place in at least 5 stages in these alloys, four of which were directly observed. This is interpreted as the result of complex Within the first 10 minutes after quenching, a period of nearly constant positron lifetime was found for those Mg-rich alloys that later show an insufficient hardness response to artificial ageing, the so-called 'negative effect'. The various processes observed could be described by two effective activation energies that were found by varying the ageing temperature from 10°C to 37°C.

Design strategy for controlled natural aging in Al–Mg–Si alloys

“…), which starts directly after quenching from solution heat treatment, the material hardness increases due to solute clustering of Mg-and Si-atoms [11][12][13][14][15]. This generates two problems for the transportation industry: first, dynamic hardening during n.a.…”

Solute-Vacancy Clustering In Al-Mg-Si Alloys Studied By Muon Spin Relaxation Technique

“…2(b) is almost independent of temperature, and there is little variation among the present samples. The temperature variations of the trapping rates of the Al-1.6%Mg 2 Si samples in Fig. 2(c) closely resemble each other in the low temperature region; the ν t decreases as temperature increases.…”

“…2) The heat treatments on the Al-1.6%Mg 2 Si samples made an effect on the trapping rates around 200 K. The largest trapping rate was found with the Al-1.6%Mg 2 Si annealed 100 • C for 1000 min, suggesting this treatment yielded the densest Mg-Si-vacancy clusters. 3) With the as quenched Al-0.5%Si sample, there formed dense Si-vacancy clusters, but theses clusters easily disappeared after the sample was stored at room temperature for 12 days.…”

“…Figures 1(a)˜1(d) show the zero-field relaxation spectra at selected temperatures with the samples of Al-1.6%Mg 2 Si as quenched, base-Al, Al-0.5%Mg and Al-0.5%Si after natural aging. It is obvious that the muon spin depolarization rates depended on temperature.…”

“…The positron annihilation spectroscopy (PAS) has been widely used for studies of defects, such vacancies, dislocations, voids, impurities, etc. [1,2], in which relatively lower (negative against surroundings) electrical potential produced by defects attract positive charged positrons. The annihilation lifetime of positron depends on the defect concentrations and the trapping rate per defect.…”