Dunwen Zuo

Effects of rare earth additions during surface boriding on microstructure and properties of titanium alloy TC21

Abstract In the present paper, the effects of rare earth (RE) additions to the solid state boriding of titanium alloy TC21 have been studied. The microstructural evolution and phase transformations of the borided layers were examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction. Moreover, the microhardness for the borided layer was also determined by Vickers hardness test. The results showed that the addition of a small amount of RE elements in the boriding process can lead to an increased boron concentration in the surface layer coupled with the improved surface hardness and coating layer thickness. Furthermore, the presence of trace quantities of RE oxide (Ce2O3) in boride layers indicated that the RE elements as catalysts could not only influence but also accelerate boriding process.

Force response characteristics and mechanical properties of friction stir welded AA2024 sheets

Process force and tensile properties in friction stir welding of AA2024 sheets were studied. Results show that the forces present a periodic variation with the same periodicity which is nearly equal to the time of one tool rotation, and thus it only depends on rotation speed. With increasing welding speed the forces increase gradually, while with increasing rotation speed the forces first decrease and then increase. Joints with superior strength-ductility synergy are produced at 900 rev min−1–300 mm min−1 and 1000 rev min−1–350 mm min−1. These joints experience nearly the same peak temperature and axial force. As heat input increases the failure initiates from the interface between nugget zone (NZ) and thermo-mechanically affected zone to heat-affected zone continuing to NZ.

Application of Stir Tool Force Measuring Dynamometer for Friction Stir Welding of Aluminum Alloys

In this study, a stir tool force measuring dynamometer was designed and manufactured to be suitable for use during the process of friction stir welding. The dynamometer meets the requirements needed for actual force measurements, with error percentage values in the x-, y-, and z-axis directions of 1.1, 1.3, and 1.2%, respectively, and a three-directional sensitivity range of 0.4–2.1%. At the same time, stir tool forces were measured under different process parameters using the manufactured dynamometer. The stir tool force mathematical model, to be used for friction stir welding processes, was established by function approximation and regression analysis methods. The model was set up with a significance level under 90%. Finally, a comparison between the model-calculated values and experimental values yielded a stir tool force average error of 10.4, 4.66, and 7.11% in the x-, y-, and z-axes direction, respectively. Therefore, calculated and experimental values are in agreement.

Study on dispersion property of sub-micro α-Al2O3 powders in water suspension by physical-chemical process

ABSTRACT Sub-micro α-Al2O3 polishing liquid is often used as the slurry in chemical mechanical polishing (CMP). At present, water is usually used as dispersion medium to disperse sub-micro α-Al2O3 powders, but the sub-micro α-Al2O3 powders easily subside in aqueous solution. In previous studies, researchers usually used single method to disperse superfine powders, however, the dispersion effect was non-ideal. In order to solve the difficult problem of sub-micro α-Al2O3 powders dispersed in water suspension, firstly, using physical method, the effects of milling time, ultrasonic time on the dispersion property of sub-micro α-Al2O3 powders in water suspension was studied by single factorial test. Then, using chemical method, the effects of dispersant type, dispersant concentration and pH value on the dispersion property of sub-micro α-Al2O3 powders in water suspension was studied by orthogonal test. Absorbance was used to evaluate the dispersion property of sub-micro α-Al2O3 powders. The results show that the optimal dispersing conditions are milling time 60 min, ultrasonic time 20 min, mass percent concentration of STPP 1% and pH value 9.