3D atom probe study of solute atoms clustering during natural ageing and pre-ageing of an Al-Mg-Si alloy

Philosophical Magazine Letters (Impact Factor: 1.27). 04/2006; DOI: 10.1080/09500830600643270
Source: OAI

ABSTRACT The pair-correlation function applied to 3D Atom Probe reconstructed volumes has been used to study the influence of a pre-ageing treatment (363 K) on the early stages of precipitation at 458K in an Al-Mg-Si 6016 alloy. Mg-Si short-range positive pair correlation (clustering) is shown to form after a pre-ageing treatment. The hetero-atomic clusters are thought to act as preferential nucleation sites and lead to a finer dispersion of precipitates after ageing.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of the study was to evaluate the accuracy of heat treatment guidelines, generally followed in industrial practices, about the T6 heat treatment of A356 aluminum alloy. In particular, the effect of the delay between quenching and artificial aging (pre-aging time) on microstructure, hardness, and tensile behavior was studied using specimens extracted from different locations of a cylinder head, characterized by different cooling rates and, consequently, by different secondary dendrite arm spacing values. Hardness and tensile tests confirmed the detrimental effect of pre-aging with a 20% reduction in hardness and strength after approximately 1 h of pre-aging, both for samples with fine and large SDAS. Differential scanning calorimetry analyses on samples that were solutionized, quenched, and pre-aged between 0 and 96 h, suggested that the nature and composition of the clusters formed during pre-aging, rather than their size, influenced the subsequent precipitation process and the final mechanical properties of the alloy.
    Journal of Materials Engineering and Performance 01/2012; 22(1). · 0.98 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Atom-probe tomography was used to investigate phase separation and copper (Cu) clustering in the ferrite phase of a 25Cr-7Ni super duplex stainless steel. The steel was subjected to a tensile load during aging at 325°C for 5800 h. The degree of phase separation into α (Fe-rich) and α′ (Cr-rich) was small, but still, it was the highest in the steel subjected to the highest load. Cu was found to cluster, and the number density of clusters increased with increasing load. In the material subjected to the highest load, Cu was enriched in regions that were neither Fe-rich nor Cr-rich. These regions also had the highest number density of Cu clusters.
    Philosophical Magazine Letters - PHIL MAG LETT. 01/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Muon spin methods are very sensitive to nanoscale defects such as trace elements and vacancies in metals. This sensitivity is required when investigating Al-Mg-Si alloys, a complicated system in which diffusion-controlled phase transformations are responsible for the most important hardening mechanisms. We present muon spin relaxation experiments conducted on Al-Mg-Si alloys at measurement temperatures in the range 20–300K. Varying the alloy composition and heat treatment, we find differences in muon depolarization in several temperature regimes. This reflects differences in concentration of several types of muon-trapping defects. We identify free solute atom and vacancy regimes, and confirm that the concentration of these defects decreases when an alloy is annealed at low temperature. We further attribute one regime to Mg-Si vacancy clustering, a mechanism required for precipitation hardening during aging. After storage at room temperature, muon trapping in this regime is more pronounced for a Mg-rich alloy than a Mg-Si-balanced alloy.
    Physical review. B, Condensed matter 09/2012; 86(10). · 3.66 Impact Factor

Full-text (2 Sources)

Available from
Jun 1, 2014