铜锡合金激光选区熔化非平衡凝固组织与性能

对具有重要工程应用价值的Cu?5%Sn合金进行激光选区熔化（SLM）成形，在激光功率160 W、扫描速度300 mm·s?1、扫描间距0.07 mm条件下，合金样品相对密度可达99.2%，熔池层与层堆积密实，表面质量良好。研究发现所获合金具有非平衡凝固组织特征，其中以α-Cu(Sn)固溶体相为主，且涉及具有超结构的γ相、δ相。显微形貌主要由柱状晶与富锡网状组织构成，伴随有不同尺度界面Sn元素偏析及晶界、晶内纳米尺寸超结构合金相颗粒析出。所获合金的力学性能与同成分铸态合金或较低Sn含量SLM合金相比得到显著强化，表面硬度可达HV 133.83，屈服强度326 MPa，抗拉强度387 MPa及断裂总延伸率22.7%。 

Nonequilibrium solidification microstructures and mechanical properties of selective laser-melted Cu-Sn alloy

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.