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Influences of Cu Content on the Microstructure and Strengthening Mechanisms of Al-Mg-Si-xCu Alloys

1
Hunan Provincial Key Defense Laboratory of High Temperature Wear-resisting Materials and Preparation Technology, Hunan University of Science and Technology, Xiangtan 411201, China
2
School of Materials Science and Engineering, Central South University, Changsha 410083, China
*
Authors to whom correspondence should be addressed.
Metals 2019, 9(5), 524; https://doi.org/10.3390/met9050524
Received: 11 April 2019 / Revised: 28 April 2019 / Accepted: 3 May 2019 / Published: 7 May 2019
(This article belongs to the Special Issue Phase Transformations in Aluminium Alloys)
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Abstract

The effects of the Cu content on the microstructure and strengthening mechanisms of the Al-Mg-Si-xCu alloys were systematically investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and mechanical tensile tests. The results show that, the strengthening mechanisms change with the Cu content. For as-quenched alloys, solution strengthening (σSS) is predominant when the Cu content ≥2.5 wt.%, and of equivalent importance as grain size strengthening (σH-P) when the Cu content ≤1.0 wt.%. With respect to peak-aged alloys, precipitation strengthening (σppt) is predominant when the Cu content ≥2.5 wt.%, but σSS becomes predominant when the Cu content is 4.5 wt.%. As the Cu content increases from 0.5 to 4.5 wt.%, the main type of precipitates in alloy tends to change from a β″ phase to Q′ phase, and then to a θ′ phase. Among the three types of precipitates, θ′-precipitate causes the largest increase in yield strength (σ0.2) and the largest decrease rate in elongation. β″-precipitate leads to the smallest increase in σ0.2 and the smallest decrease rate in elongation. The increase of Cu content reduces Si solubility in the Al matrix and thus decreases the nucleation rate of β″ phase during subsequent aging. View Full-Text
Keywords: Al-Mg-Si-Cu Alloy; Cu Content; microstructure; mechanical properties; high-resolution transmission electron microscopy Al-Mg-Si-Cu Alloy; Cu Content; microstructure; mechanical properties; high-resolution transmission electron microscopy
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Chen, Y.; Hu, Q.; Pan, S.; Zhang, H.; Liu, H.; Zhu, B.; Liu, X.; Liu, W. Influences of Cu Content on the Microstructure and Strengthening Mechanisms of Al-Mg-Si-xCu Alloys. Metals 2019, 9, 524.

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