| With the rapid development of the micro-electromechanical systems(MEMS) and electronics industry, the quantity demanded of the powder metallurgy microminiaturized products is more and more larger, which put forward new requirements for the powder metallurgy in the fabrication of microminiaturized products requiring it to high performance, high precision, low power and low cost direction. In view of the problems of the several common application of powder metallurgy technology, such as the processing cycle is long, the process is complex, the range of applicable materials is narrow and cost is high, the micro-ultrasonic powder molding method(Referred to micro-UPM) was proposed to fabricate micro parts of the low melting point alloy powder in this study. This method was used to form metal micro parts directly. Because the dimensions of the parts are extremely small, the ultrasonic energy is highly concentrated. Under the pressure of an ultrasonic sonotrode, ultrasonic vibrations are used to generate heat from the mutual compressive deformation of the alloy powder particles and the strong friction between the powder particles and the inner surface of the micro-cavity to melt the alloy powder. The powder melt in the micro-cavity is rapidly cooled to form micro parts. The micro parts contained fine grains, exhibited high density and good mechanical performance, and did not require subsequent sintering processes. Advantages of this method include a short forming cycle, low energy consumption and low production costs. This paper studies the main content includes:(1) Micro-UPM was proposed to fabricate micro parts of the Sn42Bi58 alloy powder in this study. The process of micro-UPM includes the mould assembly, powder filling and compaction, ultrasonic forming and micro parts extraction. A combined micro mold with micro cavity without channel was designed. Three kinds of Sn42Bi58 alloy micro gears were fabricated using micro-UPM. These micro gears had a clear contour, good forming quality. Thus, the feasibility of micro-UPM was verified.(2) To study the effect of ultrasonic exposure time on the microstructure of micro-UPM micro parts by the metallographic image analyser, two groups of the Sn42Bi58 alloy micro specimens were moulded using different ultrasonic exposure times and one group of specimens was heat treatable. The X-ray diffraction analysis was used to investigate the variations in the crystal phase during the formation of Sn-Bi alloy micro parts using micro-UPM. The DSC Q200 thermal analyzer was used to determine the melting temperature and melting enthalpy of micro part samples with different ultrasonic duration time. Though the tensile tests, the effect of ultrasonic exposure time on the mechanical properties of the Sn42Bi58 alloy micro parts was investigated. Reasonable process parameters for micro-UPM method were determined, which were sonotrode pressure of 63.5 MPa, ultrasonic output power of 2475 W and ultrasonic exposure time of 1.5 s. By the analysis and summary, the forming temperature distribution curve of micro-UPM was proposed.(3) Micro-UPM was used for the fabrication of copper wires/Sn–Bi eutectic alloy micro-composite(preferred to x-Cu_w/Sn–Bi, where x refers to the number of copper wires). Microstructures and tensile properties of the micro-composite were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and tensile tests. Microstructures indicated that the interface bonding of the copper wires and Sn42Bi58 alloy matrix was fairly good, which guaranteed the interface bonding strength. During the tensile tests, the micro-composite’s tensile strength increased significantly with increasing the number of copper wires; however, the elongation first improved and then decreased. The reinforced copper wires failed by two mechanisms during the tensile tests. In one mechanism, the copper wire fractured in the middle position, while in the other, it pulled out from the Sn42Bi58 alloy matrix. |
PDF Full Text Request