Study of the microstructure and mechanical properties of Cu–Sn alloys formed by selective laser melting with different Sn contents

The microstructure and the mechanical properties of α-phase Cu–5Sn alloy, Cu–10Sn alloy, and Cu–15Sn alloy (wt.%) prepared by selective laser melting have been studied in this work. Under the same process condition, the laser absorption of the alloys increases continuously with the increase in Sn content. The optimal process parameters of the three alloys were obtained by Response Surface Method. The Sn content was found to have a significant effect on the relative density of the Cu–Sn alloys, as well as the laser power. The effect of laser power on the relative density of the alloys is weakened by the increase in laser absorption as the Sn content increases. Comparing the melt pool of the three alloys, they all show mainly columnar grains. As the Sn content increases, the size of the columnar grains becomes larger, and when the Sn content reaches 15 wt%, the columnar grains can penetrate through several melt pools. With the increase of Sn content from 5 wt% to 15 wt%, the tensile strength of the alloy increased from 382 MPa to 738 MPa, but the plasticity decreased significantly and the elongation decreased from 26% to 9%. As the Sn content increases from 5 to 15 wt%, the amount of solid-soluble Sn in the α-phase alloy increases, creating a lattice distortion stress field that effectively prevents dislocation movement. Thus, the stress field effectively increasing the yield and tensile strength of the alloy. Meanwhile, the increase in Sn content leads to the appearance of many brittle, hard and rich phases on the micron scale and precipitation from grain boundaries within the lattice, resulting in an increase in strength and a decrease in plasticity of the alloy. In conclusion, Cu–10Sn alloy has more excellent tensile properties and higher yield and tensile strengths with good ductility compared to Cu–5Sn and Cu–15Sn alloys.