Impacts of Rare Earth Element La on Properties and Microstructure of AlMgSi Alloys

doi:10.11900/0412.1961.2022.00298

Acta Metall Sin

2024, Vol. 60

Issue (1): 107-116 DOI: 10.11900/0412.1961.2022.00298

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Impacts of Rare Earth Element La on Properties and Microstructure of AlMgSi Alloys

ZHENG Xiong¹, LAI Yuxiang²(

), XIANG Xuemei¹, CHEN Jianghua²

1 College of Materials Science and Engineering, Hunan University, Changsha 410082, China
2 Pico Electron Microscopy Center, Center for Advanced Studies in Precision Instruments, Hainan University, Haikou 570228, China

Cite this article:

ZHENG Xiong, LAI Yuxiang, XIANG Xuemei, CHEN Jianghua. Impacts of Rare Earth Element La on Properties and Microstructure of AlMgSi Alloys. Acta Metall Sin, 2024, 60(1): 107-116.

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Abstract

The 6xxx series aluminum alloys Al-Mg-Si(-Cu) are widely used in the automotive industry owing to their high strength-to-weight ratio, good formability, and corrosion resistance. Micro-alloying is an effective technique for enhancing the properties and microstructure of Al alloys. The effects of varying La additions on the microstructure and properties of Al-0.75Mg-0.75Si (mass fraction, %) alloy have been investigated using hardness, electrical conductivity, and tensile tests, as well as SEM and TEM. As the La content increases, the following observations are made: (1) the ductility and electrical conductivity of the alloy gradually increase due to the increase in the fraction of the AlSiLa secondary phases induced by the La addition and the amount of Si solute atoms consumed by these phases; (2) the strength of the alloy first increases due to the increase in the secondary-phase strengthening contribution of the AlSiLa phases and the grain refinement contribution, and then decreases owing to the decrease in the solid-solution strengthening contribution; and (3) the types of precipitates formed during aging gradually change; besides the β″ phase, polycrystalline β″ precipitates are also precipitated in the peak-aged alloys with La addition, while β″/U2, β′/U2, and β′/U2/β″ composite precipitates are precipitated in the over-aging condition of the La-added alloys.

Key words: Al-Mg-Si alloy micro-alloying secondary phase precipitate mechanical property electron microscopy

Received: 16 June 2022

ZTFLH:

TG113

Fund: National Natural Science Foundation of China(52001119);National Natural Science Foundation of China(51831004);National Natural Science Foundation of China(52171006)

Corresponding Authors: LAI Yuxiang, associate professor, Tel: (0898)66275138, E-mail: yxlai123@hainanu.edu.cn

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	ZHENG Xiong
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https://www.ams.org.cn/EN/10.11900/0412.1961.2022.00298 OR https://www.ams.org.cn/EN/Y2024/V60/I1/107

Table 1 Chemical compositions of the four alloys used in the experiment

Fig.1 Variations of hardness (a) and electrical conduc-tivity (b) of the four alloys aging at 180^oC (AQ—as-quenched, PA—peak-aging)

Fig.2 Engineering strain-stress curves of the four alloys under the AQ and PA conditions

Table 2 Tensile properties of the four alloys under the AQ and PA conditions

Fig.3 Back-scattered electron (BSE) images (a-d) and EBSD inverse pole figures (IPFs) (e-h) of 0La (a, e), 0.2La (b, f), 0.4La (c, g), and 0.6La (d, h) alloys under the PA condition

Fig.4 XRD spectra of the four alloys under the PA condition (a), and BSE image of the 0.4La alloy (b) and EDS result of the particle marked with dot in Fig.4b (c) (Inset in Fig.4a shows the enlarged XRD spectra in the angular range 20°-30°)

Fig.5 Secondary electron (SE) images (a-d) and corresponding BSE images (e-h) of the tensile fracture morphologies of 0La (a, e), 0.2La (b, f), 0.4La (c, g), and 0.6La (d, h) alloys under the PA condition (Arrows show the cleavage planes, blue dashed circles show the dimples, orange dashed circles show the secondary phases)

Fig.6 Typical TEM bright field images (a, c, e, g) and precipitate length distributions (b, d, f, h) of 0La (a, b), 0.2La (c, d), 0.4La (e, f), and 0.6La (g, h) alloys under the PA condition

Fig.7 Schematics of the unit cell of β", β', and U2 (a), and HAADF-STEM images of 0La (b, f) and 0.4La alloys (c-e, g-i) peak-aged (b-e) and 96 h-aged (f-i) at 180^oC (Cyan circle, orange and red hexagons depict the sub-unit(s) of β", β', and U2, respectively; z—fractional coordinate of atoms along precipitates' longest dimension; LDC—low density cylinder; a, b, c—lattice parameters)

Fig.8 Atomic-resolution HAADF-STEM image (a) and the corresponding EDS analyses (b-f) of the β″/U2 composite precipitate

Fig.9 DSC curves of the four alloys under the AQ condition

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