Heterogeneous Structure and Mechanical Properties of Strong and Tough Al Alloys Prepared by Selective Laser Melting

doi:10.11900/0412.1961.2022.00314

Acta Metall Sin

2022, Vol. 58

Issue (11): 1509-1518 DOI: 10.11900/0412.1961.2022.00314

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Heterogeneous Structure and Mechanical Properties of Strong and Tough Al Alloys Prepared by Selective Laser Melting

LIN Yan¹, SI Cheng¹, XU Jingyu¹, LIU Ze², ZHANG Cheng¹(

), LIU Lin¹

^1.State Key Lab for Materials Processing and Die & Mold Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
^2.Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan 430072, China

Cite this article:

LIN Yan, SI Cheng, XU Jingyu, LIU Ze, ZHANG Cheng, LIU Lin. Heterogeneous Structure and Mechanical Properties of Strong and Tough Al Alloys Prepared by Selective Laser Melting. Acta Metall Sin, 2022, 58(11): 1509-1518.

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Abstract

Aluminum alloys have been widely used in fields such as automotive and aerospace industries, owing to their excellent mechanical properties, lightweight, and low recycling costs. However, aluminum alloys processed by selective laser melting (SLM) typically suffer from insufficient strength and fracture toughness. To tackle this issue, a new strategy that integrates eutectic composition design and grain refinement has been adopted to create a heterogeneous structure that can improve strength and toughness of SLMed Al-Fe-Zr alloys. The SLMed AlFe₅ alloy consists of high-volume-fraction of coarse and columnar grains and low-volume-fraction of fine grains, and no obvious heterogeneity is visible across the microstructure length scale. With the addition of Zr, the volume fraction of fine grains significantly increases, leading to the heterogeneous distribution of coarse and fine grains in the SLMed AlFe₅Zr₁ alloy. Meanwhile, both AlFe₅ and AlFe₅Zr₁ alloys show a nanoscale cellular structure. This type of a nanosized cellular structure, together with supersaturated Fe and high-density dislocations, contributes to a high yield strength of 400 MPa for the SLMed AlFeZr alloys. The heterogeneous structure can further improve the strain strengthening capability, enabling a tensile strength as high as 450 MPa for the AlFe₅Zr₁ alloy. Furthermore, the heterogeneous structure promotes crack deflection and crack tip blunting, which can effectively increase crack growth resistance and impart superior fracture toughness to the AlFe₅Zr₁ alloy.

Key words: Al-Fe-Zr alloy selective laser melting (SLM) heterogeneous structure mechanical property

Received: 23 June 2022

ZTFLH:

TG146.2

Fund: National Natural Science Foundation of China(52061160483);National Natural Science Foundation of China(92166130);National Natural Science Foundation of China(52001075);China Postdoctoral Science Foundation(2021M701290)

About author: ZHANG Cheng, associate professor, Tel: (027)87558200, E-mail: czhang@hust.edu.cn

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https://www.ams.org.cn/EN/10.11900/0412.1961.2022.00314 OR https://www.ams.org.cn/EN/Y2022/V58/I11/1509

Fig.1 Schematics of the plate tensile (a) and the single-edge-notch tension (b) specimens (unit: mm. L—length of specimen, B—thickness of specimen, W—width of specimen, a—length of crack)

Fig.2 Relative densities of SLMed AlFe₅Zr₁ alloy with different processing parameters (a), and reconstructed 3D X-ray computed tomography (CT) image representing porosity distribution within the AlFe₅Zr₁ alloy prepared with the best SLM processing procedure (b) (SLM—selective laser melting)

Fig.3 EBSD images (a, b), pole figures (c, d), and grain size distributions (e) of SLMed AlFe₅ (a, c) and AlFe₅Zr₁ (b, d) alloys

Fig.4 Bright-field TEM images (a, c), high-angle annular dark field (HAADF) images (left) and corresponding EDS element mappings of rectangle (right) (b, d) of SLMed AlFe₅ (a, b) and AlFe₅Zr₁ (c, d) alloys (Inset in Fig.4c shows the corresponding selected area electron diffraction (SAED) pattern)

Fig.5 Room temperature quasi-static tensile engineering stress-strain curves of the SLMed AlFe₅, AlFe₅Zr₁, and AlSi₁₀Mg alloys

Table 1 Tensile properties of the SLMed AlFe₅, AlFe₅Zr₁, and AlSi₁₀Mg alloys

Fig.6 Load-displacement curves of the SLMed AlFe₅, AlFe₅Zr₁, and AlSi₁₀Mg alloys

Fig.7 Bright-field TEM images showing tension-induced microstructure evolution in the SLMed AlFe₅Zr₁ alloy

Fig.8 Crack profiles characterized on the surface of the SLMed AlFe₅Zr₁ alloy at different stages of crack extension (a-d), and 3D fracture surface morphologies for the SLMed AlFe₅Zr₁ (e) and AlFe₅ (f) alloy samples after fracture toughness testing
(a) 270 N (b) 275 N (c) 290 N (d) 295 N

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