Effect of Adding Methods of Nucleating Agent on Microstructure and Mechanical Properties of Zr Modified Al-Cu-Mg Alloys Prepared by Selective Laser Melting
WANG Kaidong, LIU Yunzhong(), ZHAN Qiangkun, HUANG Bin
National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510640, China
Cite this article:
WANG Kaidong, LIU Yunzhong, ZHAN Qiangkun, HUANG Bin. Effect of Adding Methods of Nucleating Agent on Microstructure and Mechanical Properties of Zr Modified Al-Cu-Mg Alloys Prepared by Selective Laser Melting. Acta Metall Sin, 2022, 58(10): 1281-1291.
Selective laser melting (SLM) technology is gaining increasing attention in the field of additive manufacturing. Al-Cu-Mg alloy parts manufactured using SLM technology exhibit significant advantages in lightweight design and the integrated formation of complex structural parts in the aerospace field. However, because of their wide freezing ranges, Al-Cu-Mg alloys have a high cracking tendency at a high cooling rate. SLM technology was used to prepare Zr-modified Al-Cu-Mg alloys in this study. Al3Zr particles were synthesized to directly add to Al-Cu-Mg alloy powders, and ZrH2 particles were chosen to form Al3Zr in-situ during SLM processes. The differences between the effects of adding Al3Zr particles directly and forming Al3Zr in-situ on the microstructures and the mechanical properties of SLMed Al-Cu-Mg alloys were analyzed. The results show that the common hot tearing in as-built Al-Cu-Mg alloys all disappear due to the addition of Al3Zr nucleating agent and the in-situ formed Al3Zr is more conducive to refining grains and improving the plasticity and the processing efficiency of SLMed Al-Cu-Mg alloys. When the laser energy density is 370 J/mm3, the grain size of the samples containing Al3Zr and in-situ formed Al3Zr particles are 1.88 and 1.28 μm, respectively. L12-Al3Zr and undissolved or unmelted Al3Zr particles are the nucleation particles generated by initial Al3Zr particles; whereas, they are all metastable Al3Zr (L12-Al3Zr) synthesized in-situ. L12-Al3Zr has a better nucleation ability than initial Al3Zr particles. The ultimate strength of the heat-treated samples with initial Al3Zr particles or in-situ formed Al3Zr can reach (493 ± 2) or (485 ± 10) MPa, respectively. The elongation of the samples with the in-situ formed Al3Zr is more than 30% higher than that of the samples containing Al3Zr particles. SLMed Al-Cu-Mg alloys with in-situ formed Al3Zr are more suitable for medium-high-speed processes because strong Marangoni flow aroused by high laser energy density is unnecessary for in-situ formed Al3Zr to realize the dispersion of the grain refiner.
Fund: Research and Development Program Project in Key Areas of Guangdong Province(2019B090907001);Major Special Project for Science and Technology Program of Guangdong Provinces(2014B010129002)
About author: LIU Yunzhong, professor, Tel: (020)87110081, E-mail: yzhliu@scut.edu.cn
Fig.1 Morphologies of coarse ZrH2 particles (a), high-pure Al powders (b), Al3Zr particles (d), fine ZrH2 particles (e), and Al-Cu-Mg alloy powders (f), and XRD spectrum of Al3Zr particles (c)
Fig.2 Low (a, c) and high (b, d) magnified morphologies of Al3Zr/Al-Cu-Mg (a, b) and ZrH2/Al-Cu-Mg (c, d) alloy composite powders
Fig.3 Cross-sectional OM images of as-built Al-Cu-Mg (a, d), Al3Zr/Al-Cu-Mg (b, e), and in-situ Al3Zr/Al-Cu-Mg (c, f) alloys prepared with the laser energy density of 370 J/mm3 (a-c) and 154 J/mm3 (d-f)
Fig.4 Relative densities of as-built Al-Cu-Mg alloys with or without nucleating agents
Fig.5 Microstructures of vertical-section in as-built Al-Cu-Mg (a, d), Al3Zr/Al-Cu-Mg (b, e), and in-situ Al3Zr/Al-Cu-Mg (c, f) alloys prepared with the laser energy density of 370 J/mm3
Fig.6 Inverse ploe figures (IPFs) (a-c) and grain size distribution images (d-f) of the vertical-section of Al-Cu-Mg (a, d), Al3Zr/Al-Cu-Mg (b, e), and in-situ Al3Zr/Al-Cu-Mg (c, f) alloys prepared with the laser energy density of 370 J/mm3 (Insets in Figs.6e and f are partial enlarged figures)
Fig.7 XRD spectra of as-built Al-Cu-Mg alloys with or without nucleating agents
Fig.8 Bright field TEM image (a), SAED patterns of L12-Al3Zr/Al with (b) or without (c) coherent interface, and EDS element maps (d) of as-built Al3Zr/Al-Cu-Mg alloys prepared with the laser energy density of 370 J/mm3
Fig.9 Bright field TEM image (a) and SAED patterns of L12-Al3Zr/Al interface along [001]Al (b) and [112]Al (c) of as-built in-situ Al3Zr/Al-Cu-Mg alloys prepared with the laser energy density of 370 J/mm3
Fig.10 SEM backscatter images of as-built Al3Zr/Al-Cu-Mg (a, c) and in-situ Al3Zr/Al-Cu-Mg (b, d) alloys prepared with the laser energy density of 370 J/mm3 (a, b) and 154 J/mm3 (c, d) (Inset in Fig.10a shows the L12-Al3Zr precipitates)
Element
Mass fraction
Atomic fraction
Al
52.86
78.41
Cu
2.63
1.66
Mg
0.34
0.55
Zr
44.17
19.38
Table 1 EDS analysis results of agglomerated phases in Fig.10c
Fig.11 SEM backscatter images of heat-treated Al3Zr/Al-Cu-Mg (a) and in-situ Al3Zr/Al-Cu-Mg (b) alloys prepared with the laser energy density of 370 J/mm3
Fig.12 Mechanical properties of Al-Cu-Mg alloys with different components in as-built condition (a) and heat-treated condition (b) prepared with different laser energy density (UTS—ultimate tensile strength, YS—yield strength, El—elongation)
Fig.13 Fracture morphologies of Al3Zr/Al-Cu-Mg (a, c) and in-situ Al3Zr/Al-Cu-Mg (b, d) alloys in the as-built condition (a, b) and after heat-treated condition (c, d) prepared with the laser energy density of 370 J/mm3 (Insets show the fracture morphologies at high magnifications)
Fig.14 Schematics of Zr phase evolution in as-built Al3Zr/Al-Cu-Mg (a) and in-situ Al3Zr/Al-Cu-Mg (b) alloys
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