Formability and Mechanical Properties of High-Strength Al-(Mn, Mg)-(Sc, Zr) Alloy Produced by Selective Laser Melting
GENG Yaoxiang(), TANG Hao, XU Junhua, ZHANG Zhijie, YU Lihua, JU Hongbo, JIANG Le, JIAN Jianglin
School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
Cite this article:
GENG Yaoxiang, TANG Hao, XU Junhua, ZHANG Zhijie, YU Lihua, JU Hongbo, JIANG Le, JIAN Jianglin. Formability and Mechanical Properties of High-Strength Al-(Mn, Mg)-(Sc, Zr) Alloy Produced by Selective Laser Melting. Acta Metall Sin, 2022, 58(8): 1044-1054.
Selective laser melting (SLM) has been widely used in many fields owing to its high manufacturing accuracy and excellent performance. A rapid solidification rate of 103-106 K/s is achieved during the SLM process, resulting in unique microstructures and highly supersaturated solid solutions beyond the normal solubility limits of alloying elements, thereby providing new opportunities for the development of microstructures and optimization of their properties. To date, SLM has been used for manufacturing a wide range of metallic materials, such as Ti-based alloys, superalloys, and stainless steel. However, specific difficulties are associated with melting aluminum powder using a laser owing to the high laser reflectivity, tenacious surface oxide, poor spreadability (particularly of low-density aluminum powder), high thermal conductivity, and large freezing ranges of many aluminum alloys. Consequently, high-strength aluminum alloys, such as the 2xxx, 6xxx, and 7xxx series, exhibit poor SLM formability. The SLM-formed aluminum alloys that are practically applied in industries at present are limited to the Al-Si base and Al-Mg-(Sc, Zr) alloys. Al-Mg-(Sc, Zr) alloys achieve high strength and ductility with low mechanical anisotropy, thus showing considerable advantages over conventional and SLM-formed Al-Si-Mg alloys. However, the strength of the present SLM-formed aluminum alloys is still lower than that of conventional high-performance ones. Based on the technical characteristics of liquid quenching in SLM, this study focuses on designing high-strength Al-(Mn, Mg)-(Sc, Zr) aluminum alloys specifically for SLM by simultaneously increasing the (Mn + Mg) and (Sc + Zr) contents. The effect of aging treatment on the microstructure and mechanical properties of the SLM-formed alloy was systematically studied. Results show that the alloy exhibits good SLM formability with a relative density of more than 99.0%. A typical multilayer distribution of laser tracks generated in the SLM process can be observed. Few columnar grains are observed in the center of the molten pool, and numerous equiaxed grains are present in molten pool boundaries with an average grain size of 4 μm. The mechanical properties of the alloys are considerably improved after aging treatment at a low temperature (≤ 350°C) owing to the precipitation of Al3Sc nanoparticles. The maximum Vickers hardness, maximum compressive yield strength, and maximum compressive strength of the aged alloy are (218 ± 5) HV, (653 ± 3) MPa, and (752 ± 7) MPa, respectively, with a compressive elongation of greater than 60% for all samples, higher than that of most SLM-formed aluminum alloys and T6-treated AA7075 alloys. Combining various strengthening mechanisms facilitates SLM-formed Al-(Mn, Mg)-(Sc, Zr) alloys with high strength.
Fund: National Natural Science Foundation of China(52001140);National Natural Science Foundation of China(51801079);Natural Science Foundation of Jiangsu Province(BK20180985);Natural Science Foundation of Jiangsu Province(BK20180987)
About author: GENG Yaoxiang, associate professor, Tel: (0511)84401184, E-mail: yaoxianggeng@163.com
Table 1 Chemical compositions of Al-(Mn, Mg)-(Sc, Zr) powder and selective laser melting (SLM)-formed specimen
Fig.1 Surface (a) and section (b) SEM images of Al-(Mn, Mg)-(Sc, Zr) powder (Inset in Fig.1a shows the size distribution of powder, D50—average particle diameter)
Fig.2 Photography of SLM-formed Al-(Mn, Mg)-(Sc, Zr) samples
Fig.3 Evolution of the relative density of the SLM-formed Al-(Mn, Mg)-(Sc, Zr) samples with the scanning rate
Fig.4 OM and upper surface SEM images (insets) of the SLM-formed Al-(Mn, Mg)-(Sc, Zr) samples manufacturing at the scanning rates of 700 mm/s (a), 900 mm/s (b), and 1100 mm/s (c)
Fig.5 Longitudinal section OM (a) and SEM (b) images of the SLM-formed Al-(Mn, Mg)-(Sc, Zr) sample manufacturing at a scanning rate of 900 mm/s (Inset in Fig.5b shows the composition analysis (atomic fraction) of precipitates)
Fig.6 EBSD orientation map (a) and pole figures (b) of the SLM-formed Al-(Mn, Mg)-(Sc, Zr) sample manufacturing at a scanning rate of 900 mm/s
Fig.7 OM images of SLM-formed Al-(Mn, Mg)-(Sc, Zr) samples aged at 200oC (a), 300oC (b), 400oC (c), and 500oC (d) for 2 h
Fig.8 SEM images of molten pool of SLM-formed Al-(Mn, Mg)-(Sc, Zr) samples aged at 200oC (a), 300oC (b), 400oC (c), and 500oC (d) for 2 h
Fig.9 XRD spectra (a) and local enlargement (b) of the SLM-formed Al-(Mn, Mg)-(Sc, Zr) samples aged at different temperatures for 2 h
Fig.10 Vickers hardnesses (a), compressive true stress-true strain curves (b), compressive mechanical properties (c) of SLM-formed Al-(Mn, Mg)-(Sc, Zr) samples aged at different temperatures for 2 h, and a comparison with others aluminum alloys (d)
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