铜锡合金激光选区熔化非平衡凝固组织与性能

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

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%.

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 theα-Cu(Sn)solid solution is the major phase along withγandδphases.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.