Nonequilibrium solidification microstructures and mechanical properties of selective laser-melted Cu–Sn alloy
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摘要: 對具有重要工程應用價值的Cu?5%Sn合金進行激光選區熔化（SLM）成形，在激光功率160 W、掃描速度300 mm·s?1、掃描間距0.07 mm條件下，合金樣品相對密度可達99.2%，熔池層與層堆積密實，表面質量良好。研究發現所獲合金具有非平衡凝固組織特征，其中以α-Cu(Sn)固溶體相為主，且涉及具有超結構的γ相、δ相。顯微形貌主要由柱狀晶與富錫網狀組織構成，伴隨有不同尺度界面Sn元素偏析及晶界、晶內納米尺寸超結構合金相顆粒析出。所獲合金的力學性能與同成分鑄態合金或較低Sn含量SLM合金相比得到顯著強化，表面硬度可達HV 133.83，屈服強度326 MPa，抗拉強度387 MPa及斷裂總延伸率22.7%。Abstract: Cu-based alloys can be used as a selective laser melting (SLM) material for advanced engineering applications, such as aerospace, 5G mobile networks, and high-speed transportation. The mechanical properties and solidification microstructures of Cu alloys prepared using the casting technique differ from those prepared using the SLM technique, and SLM-built alloys can involve more complex microstructures and phase transformations developed in micromolten pools produced by high-power laser beams. However, nonequilibrium solidification microstructures and mechanical properties of SLM-built Cu–Sn alloys have seldom been studied in the literature. In this work, the Cu–5%Sn alloy was investigated using the SLM technique, along with cast Cu–Sn alloys for comparison. The high quality Cu-based alloy samples were fabricated using the SLM technique, with optimized processing parameters of 160 W laser power, 300 mm·s?1 scanning speed, and 0.07 mm line spacing. The samples exhibit a relative density of 99.2%, and virtually no pores and spheroidizing phenomena or warping defects were observed. The microstructural analysis of SLM-built Cu–5% Sn alloy reveals a nonequilibrium solidification feature under high cooling rates and rapid alternative thermal conditions during the SLM fabrication process, in which the α-Cu(Sn) solid solution is the major phase along with γ and δ phases. Columnar grains and reticular microstructures dominate the solidified SLM-built alloy, while segregated Sn appears in the boundaries of all levels within the alloys. The Sn-rich nanoparticles with super-lattice structures precipitates along the grain boundaries and inside the grains. With the combined effects of grain fining, super-lattice-structured nanoparticles precipitation, solid solution, and thermal residual stress, the SLM-built Cu–5%Sn alloy shows significantly enhanced mechanical properties, such as HV 133.83 Vickers hardness, 326 MPa yield strength, 387 MPa tensile strength, and 22.7% fracture extension. Such scientific information is very useful for improving the alloy composition design and optimizing the SLM processing parameters.
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圖 1 SLM成形Cu?5%Sn合金及表面光學顯微觀察。（a）SLM成形塊體；（b）頂表面形貌；（c）側表面形貌
Figure 1. Cu–5%Sn alloy prepared using the SLM technique and corresponding optical observation of the alloy surfaces: (a) SLM built block; (b) top surface image; (c) side surface image
圖 2 氣霧化Cu?5%Sn合金粉末與SLM成形合金X射線衍射圖譜
Figure 2. X-Ray diffraction patterns for atomized prealloyed powder and as-built Cu–5%Sn
圖 3 SLM成形Cu?5%Sn合金掃描電子顯微分析。（a）橫截面；（b）縱截面
Figure 3. Scanning electron microscopy (SEM) image of Cu–5%Sn alloy prepared using the selective laser melting technique: (a) transverse cross-section; (b) longitudinal cross-section
圖 4 銅錫二元合金平衡相圖[22]及本文研究所獲Cu?5%Sn合金鑄態組織
Figure 4. Cu–Sn equilibrium binary phase diagram and microstructure of as-cast Cu–5%Sn alloys
圖 5 SLM成形Cu?5%Sn合金樣品透射電子顯微分析。（a）明場像；（b）選區電子衍射；（c）暗場像；（d）高角環形暗場像
Figure 5. Transmission electron microscopy (TEM) image of the Cu–5%Sn alloy fabricated using the selective laser melting technique: (a) bright field image; (b) selected area electron diffraction; (c) dark field image; (d) high angle annular dark field image
圖 6 α相、β相、γ相、δ相單胞(001)面示意圖
Figure 6. Schematic of (001) faces for lattice of α, β, γ, and δ phases
圖 7 Cu?5%Sn合金SLM成形樣品準靜態拉伸試驗工程應力?應變曲線圖
Figure 7. Engineering stress–strain curves of the SLM-built Cu–5% Sn alloy using quasistatic tensile tests
表 1 Cu?5% Sn合金激光選區熔化成形參數與相對密度匯總
Table 1. Selective laser melting parameters and corresponding relative densities of as-prepared Cu–5% Sn alloys
Experimental number Laser power/
WScanning speed/
(mm·s?1)Line spacing/
mmEnergy density/
(J·mm?3)Relative density/% 1 120 300 0.03 666.66 91.47 2 120 600 0.05 200.00 90.77 3 120 900 0.07 95.24 91.09 4 140 600 0.07 166.66 95.77 5 140 900 0.03 259.26 93.36 6 140 300 0.05 466.66 96.34 7 160 300 0.07 380.96 99.19 8 160 600 0.03 444.44 96.28 9 160 900 0.05 177.78 94.70 R 5.61 2.62 1.65 
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