The evolution of precipitate crystal structures in an Al-Mg-Si(-Cu) alloy studied by a combined HAADF-STEM and SPED approach

Abstract

This work presents a detailed investigation into the effect of a low Cu addition (0.01 at.%) on precipitation in an Al-0.80Mg-0.85Si alloy during ageing. The precipitate crystal structures were assessed by scanning transmission electron microscopy combined with a novel scanning precession electron diffraction approach, which includes machine learning. The combination of techniques enabled evaluation of the atomic arrangement within individual precipitates, as well as an improved estimate of precipitate phase fractions at each ageing condition, through analysis of a statistically significant number of precipitates. Based on the obtained results, the total amount of solute atoms locked inside precipitates could be approximated. It was shown that even with a Cu content close to impurity levels, the Al-Mg-Si system precipitation was significantly affected with overageing. The principal change was due to a gradually increasing phase fraction of the Cu-containing Q -phase, which eventually was seen to dominate the precipitate structures. The structural overtake could be explained based on a continuous formation of the thermally stable Q -phase, with Cu atomic columns incorporating less Cu than what could potentially be accommodated.

Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM): From Scanning Nanodiffraction to Ptychography and Beyond

“…The combination of scanning diffraction measurements, PED, and sample tilt to create 3D orientation tomographic reconstructions was shown by Eggeman et al (2015). Other extensions to orientation mapping include applying principal component analysis and machine learning techniques to orientation measurements in 4D-STEM datasets, for example in studies by Sunde et al (2018) and Ånes et al (2018). Figure 3e shows simultaneously recorded phase and orientation maps for LiFePO4, from an experiment performed by Brunetti et al (2011) using PED and the spot matching method.…”

Influence of Short-Term Heat Treatment on the Mechanical Properties of Al–Mg–Si Profiles

“…The resulting phases after casting, like Al 5 FeSi, are well-known and investigated by several authors [21][22][23]. The process of precipitation and the hardening phases during NA and AA have been investigated by Mondolfo [24] and other authors [25][26][27][28][29]. To analyze the different phases in detail, using another etching and a TEM is irreplaceable for further investigations.…”

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“…Результаты исследований и их обсуждение. В сплаве 6013 системы Al-Mg-Si-Cu выделяются две равновесные фазы: кубическая  (Mg2Si) − фазы (пространственная группа Fm3m типа CaF2 с периодом решетки а = 0,639 нм) и гексагональная Q (Al5Cu2Mg8Si6) − фаза с периодами решетки а = 1,032 нм; с = 0,405 нм) [14][15][16]. В работе [17] методами дифференциальной сканирующей калориметрии, просвечивающей электронной микроскопии, рентгеноструктурного анализа [18] построена диаграмма фазовых превращений при старении сплава 6013, на которой нанесены области существования фаз βи Qтипа (рис.1).…”