A micro-ultrasonic powder moulding method to fabricate Sn–Bi alloy micro parts

•Micro-UPM was proposed and adopted to fabricate Sn–Bi alloy micro parts.•The feasibility of micro-UPM was verified by fabricating micro gears.•The reasonable process parameters for micro-UPM were determined.•The forming mechanism of micro-UPM was proposed. The Sn–Bi eutectic alloy powder in the micro-cavity was melted by ultrasonic vibration and rapidly cooled to form micro parts; no subsequent sintering process was required. Three kinds of Sn–Bi alloy micro gears were successfully fabricated, which verified the feasibility of the micro-ultrasonic powder moulding method. The effect of ultrasonic exposure time on the microstructure and mechanical properties of the micro parts was investigated respectively by metallographic analysis, XRD and tensile testing. Reasonable process parameters for this method were determined, which were sonotrode pressure of 63.5MPa, ultrasonic output power of 2475W and ultrasonic exposure time of 1.5s.