Characterization of the Density and Spatial Distribution of Dispersoids in Al-Mg-Si Alloys

Abstract

Al-Mg-Si alloys often contain small additions of, for example, Mn or Cr, to form dispersoids, which may act as nucleation sites for Mg2Si particles after homogenization. The purpose of adding Mn and Cr is to ensure a high density of uniformly distributed small β’-particles, which can be dissolved during further processing prior to the final age hardening step. However, their density and spatial distribution are critically dependent on the homogenization procedure. It is therefore important to have a robust and reliable method for assessing their spatial distribution. In the present work, an existing methodology for assessing spatial uniformity, the Global Shannon Entropy (GSE), was implemented and evaluated for different dispersoid structures characterized by scanning electron microscopy. This metric is highly dependent on the parameters used, but by careful selection of adequate parameters, it can be effective in detecting non-uniformity. An important weakness with the GSE was identified, and a modification to improve on the ability to differentiate degrees of non-uniformity is suggested. To evaluate the proposed methodology, the effect of heating rate on dispersoid precipitation behaviour during homogenisation of four Al-Mg-Si alloys with different Mn/Cr-content was investigated. In general, the dispersoid density increased with decreasing heating rates as longer times in the furnace resulted in particle coarsening. Slower heating rates were found to promote a more uniform dispersoid structure for most alloys investigated in this study. The metric with the new term demonstrated promising results, and improved the ability to differentiate degrees of spatial uniformity.

Investigation of microstructure, hardness and residual stresses of wire and arc additive manufactured 6061 aluminium alloy

“…Their effect on mechanical behaviour comes from the following phenomena: they may act as nucleation sites for β-particles (Mg2Si) after homogenisation. Therefore, a high number density and a uniform size distribution of small β-particles lead to a better dissolution during further heat treatment prior to the final age hardening step [80]. High temperature (up to 400°C) are repetitively applied during WAAM process, which could explain the presence of large dispersoids.…”

Effect of Dispersoids and Intermetallics on Hardening the Al‐Si‐Cu‐Mg Cast Alloys

“…e effect of Cr and Mn addition and heat treatment on AlSi3Mg casting alloy was investigated by Tocci et al [3] who found that Cr-and Mn-based dispersoid particles improve Vickers microhardness of the aluminum matrix compared to the base alloy after solution treatment and quenching, which is in accordance with the dispersion-hardening mechanism. In a similar study, Remøe et al [4] recommended decreasing heating rates which would increase the dispersoid density.…”

Dispersoids in Al-Mg-Si Alloy AA 6086 Modified by Sc and Y

“…Their properties can be improved by Zr-additions [45,46]. Remoe et al [47] revealed that in Al-Mg-Si alloys with different Mn-contents, the heating rates affect the density and spatial distribution of α-AlMnSi dispersoids. It was found that the additions of Cd [48] and Mo [49] can enhance the elevated properties of 3xxx alloys.…”