Papers by Author: Dang Hui Wang

Abstract: The corrosion resistance of Ultra-fine grain (UFG) chromium bronze, prepared by Equal-channel angular pressing (ECAP) processing, was investigated in HCl solution at room temperature and atmospheric pressure by electrochemistry technique and immersion experiment. The results shows that the corrosion potential of chromium bronze is decreased with ECAP processing. But the corrosion resistance is deteriorated slightly. According to the immersion tests, the weight-loss of UFG chromium bronze, compared with its counterpart, is higher in the initial stage and lower in the later stage, and the gap is in the range of 5%-15%. The corrosion mechanism on the UFG chromium bronze is deduced from the experiment data and corrosion morphology.

Abstract: The effects of the atomizing pressure on the microstructures and properties of the lead-free solder powder by the supersonic atomizer method were investigated. The microstructures of the brazed joint of solder paste were also observed. The results showed that with increasing atomizing pressures from 0.4 to 0.7 MPa, the powder particles are refined significantly and the effective atomization efficiency increases rapidly, but the oxygen content slightly rises. When the atomizing pressures increases from 0.7 to 0.9 MPa, the effective atomization efficiency only increases slightly, meanwhile both sphericity and roughness of the powder deteriorate. The atomized powder exhibits high effective atomizing efficiency, uniform size distribution, good sphericity and smooth surface when the atomizing pressure is 0.7 MPa. The diffusion layer brazed welded by Sn3Ag2.8Cu paste with Cu substrate is thicker and more irregular than that of by Sn37Pb paste.

Abstract: An investigation on the melt delivery tube tip pressure and the effective atomizing efficiency of atomizing powder was carried out. The results show that all of melt delivery tube tip pressures are negative value in the atomization gas pressure range of 0.4~0.9 MPa, and they monotonously increase with increasing the atomizing pressure; when the atomizing pressure is higher than 0.7 MPa, the negative pressure of the melt delivery tube tip is slowly increasing with continuously increasing the atomizing pressure; the atomized powder possesses higher effective atomizing efficiency, more uniform size distribution, better sphericity and smoother surface at the atomizing pressure of 0.7 MPa and the pressure of the melt delivery tube tip of -39.44 kPa.

Abstract: The microstructures and properties of Sn3Ag2.8Cu and Sn3Ag2.8Cu-0.1Ce solder alloys were investigated by means of OM, SEM and EDX and compared to that of Sn37Pb. The results show that the wettability of Sn3Ag2.8Cu-0.1Ce is more favorable, Sn3Ag2.8Cu exhibits poorer wetting behaviour compared to that of Sn37Pb solder; the conductivities of Sn3Ag2.8Cu-0.1Ce and Sn3Ag2.8Cu soldesr are almost 20 percent and 8 percent higher than that of Sn37Pb respectively; the fractography of tensile specimen of Sn3Ag2.8Cu is smooth and light, and is a quasi-cleavage fracture mechanism, whereas that of Sn3Ag2.8Cu-0.1Ce is dark and rough, and has a fibrous pattern, and is a ductile fracture mechanism; the fractography of Sn3Ag2.8Cu-0.1Ce includes more compact and more uniform dimples than that of Sn3Ag2.8Cu, this is cause of the trace amounts of Ce refining the microstructure; brazing with the Cu substrate, the diffusion layer of Sn3Ag2.8Cu solder with Cu substrate includes more irregular IMC compared to Sn3Ag2.8Cu-0.1Ce and Sn37Pb..