Control of peritectic phase content and its effect on properties of CuSn20P1 alloy by semi-solid rheological forming

CuSn20P1 alloy has a wide range of applications in aerospace, automobile and other fields, but the mismatch between strength and plasticity in conventional casting has greatly limited its application field. In the paper, a melt enclosed cooling slope channel (ECSC) was used to prepare CuSn20P1 alloy semi-solid slurry, and then the casting was prepared by rheo-squeeze casting (RSC) and liquid squeeze casting (LSC). The effect of high mold temperature (500 °C, 525 °C, 550 °C, 575 °C) on peritectic phase content and properties of CuSn20P1 alloy was studied. The results show that the higher mold temperature is conducive to the formation of peritectic β phase, and the content of peritectic β phase increases from 36.18% to 57.88% with the mold temperature increasing from 500 °C to 575 °C. Interestingly, the δ-phase content decreased significantly with the increase in mold temperature. In addition, the β are tightly bound to the α-Cu and exist semi-coherent interface matching in (101) β //(-1-10) α-Cu . On the contrary, the β/δ interface is clear and well-bonded but no orientation relationship exists. The tensile strength and elongation increase from 282.9 MPa to 0.16% to 346.9 MPa and 0.26% with the mold temperature from 500 °C to 575 °C, respectively. The tensile strength and elongation of RSC at 575 °C are 29.3% and 116.7% higher than those of LSC-550, respectively. It is likely attributed to increased peritectic phase content with the semi-coherent interface, fine grain strengthening, and solid solution strengthening. Moreover, the fracture mechanism indicates that the peritectic phase can effectively prevent crack propagation. This work can make a significant contribution to the preparation of Cu alloy casting with high performance and high Sn content.