Mechanical Properties of AlSiMg Alloy Specifically Designed for Selective Laser Melting
GENG Yaoxiang(), FAN Shimin, JIAN Jianglin, XU Shu, ZHANG Zhijie, JU Hongbo, YU Lihua, XU Junhua
School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
Cite this article:
GENG Yaoxiang, FAN Shimin, JIAN Jianglin, XU Shu, ZHANG Zhijie, JU Hongbo, YU Lihua, XU Junhua. Mechanical Properties of AlSiMg Alloy Specifically Designed for Selective Laser Melting. Acta Metall Sin, 2020, 56(6): 821-830.
Using complex shapes and precise structural parts is becoming a strong trend in modern advanced manufacturing. However, traditional manufacturing technology hardly achieves the complex geometric parts directly. Selective laser melting (SLM) is an advanced manufacturing technology for metallic materials, enables production parts with complex geometry combined with the enhancement of design flexibility. The cooling rate of molten pool can reach 103~106 K/s during the SLM process. In this case, the solid solubility of the alloying elements in the matrix can be greatly enhanced. Aluminum alloy has been widely used in industry. At present, the strength of SLM-formed aluminum alloys is far lower than that of high-strength aluminum alloys obtained from a traditional process. It is necessary to develop high-strength aluminum alloy composition based on SLM technical characteristics. The present study is devoted to design high-strength AlSiMg1.5 aluminum alloy specifically for SLM using the local structure model based on the liquid-solid structural compatibility of the alloy and the technical characteristics of the liquid quenching in SLM. The effect of the ageing treatment on the microstructure, the hardness, and the compressive properties of the SLM-formed AlSiMg1.5 alloy was systematically studied. Almost completely dense samples were obtained by adjusting the parameters of SLM process. When the ageing temperature was 300 ℃, the super-solid solution Si precipitated and grew in the island-like Al-rich structure, and the reticular Si-rich structure decomposed and spheroidized gradually with the increases of ageing time of SLM-formed AlSiMg1.5 samples. In this case, the hardness and the strength of the samples decreased, but the elongation increased significantly. The microstructures of the SLM-formed AlSiMg1.5 samples did not change obviously when the ageing temperature was 150 ℃. But the hardness and yield strength of the samples significantly increased first and then decreased slightly. The maximum microhardness and compressive yield strength of SLM-formed AlSiMg1.5 samples aged at 150 ℃ were (169±1) HV and (453±4) MPa, respectively, and the elongation of samples exceeds 25%. In this study, a special Al91.0Si7.5Mg1.5 (mass fraction, %) aluminum alloy specifically for SLM with excellent formability and mechanical properties was designed.
Fund: National Key Research and Development Program of China(2016YFB1100103);National Natural Science Foundation of China(51801079);Natural Science Foundation for Young Scientists of Jiangsu Province(BK20180985);Natural Science Foundation for Young Scientists of Jiangsu Province(BK20180987);Natural Science Foundation in Higher Education of Jiangsu Province(18KJB430011)
Fig.1 [Si-Al12] (a) and [Si-Mg8] (b) clusters in the α-(Al, Si) and Mg2Si phases, respectively Color online
Powder
Si
Mg
Fe
Al
Designed chemical composition
7.5
1.5
0.0
Bal.
Actual chemical composition
8.1
1.4
0.2
Bal.
Table 1 Comparison of the designed and actual chemical compositions of the AlSiMg powders
Fig.2 SEM image (a) and size distribution (b) of AlSiMg1.5 powders (Dv is the measured particle diameter, and 10, 50 and 90 are the volume percentages of particles with a diameter smaller than the Dv values)
Fig.3 Photography of SLM-formed AlSiMg1.5 samples (SLM—selective laser melting)
Fig.4 Longitudinal section OM images of the AlSiMg1.5 samples manufactured at scanning speeds of 800 mm/s (a) and 1200 mm/s (b) with laser power of 300 W
Fig.5 Evolution of the porosity of the SLM-formed AlSiMg1.5 samples with the laser energy and the scanning speed at a laser power of 200 and 300 W
Fig.6 Longitudinal section SEM image of SLM-formed AlSiMg1.5 sample
Fig.7 TEM bright field image (a) of SLM-formed AlSiMg1.5 sample and corresponding EDS mapping of Al (b), Si (c) and Mg (d) Color online
Fig.8 SEM images of SLM-formed AlSiMg1.5 samples after ageing at 300 ℃ for 0 h (a), 0.5 h (b), 1 h (c), 1.5 h (d), 2 h (e) and 3 h (f)
Fig.9 SEM images of SLM-formed AlSiMg1.5 samples after ageing at 150 ℃ for 18 h (a) and 48 h (b)
Fig.10 XRD spectra of the SLM-formed AlSiMg1.5 samples with different ageing conditions
Fig.11 Evolution of the Vickers hardness of the SLM-formed AlSiMg1.5 samples after ageing at 150 and 300 ℃ for different time
Fig.12 Compressive stress-strain curves (a) and mecha-nical properties (b) of SLM-formed AlSiMg1.5 samples with different ageing conditions (Inset in Fig.12a shows the photography of SLM-formed AlSiMg1.5 samples before and after com-pression)
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