Papers by Author: Mei Li

Abstract: Fractal analysis based on results of high temperature X-ray diffraction experiment was used to study the temporal-spatial properties of particles in In-40wt.%Sn melt. Partially-overlapping multirange fractal structure is observed in In-40wt.%Sn melt, and as temperature decreases from 800°C to 130°C, low fractal dimension was found to range between 2.000 and 2.669, high fractal dimension is still 3.000 without alteration. Moreover, low fractal dimension reveals a discontinuous change between 600°C and 700°C. Fractal characteristics of In-40wt.%Sn melt were correlated with the evolution of microstructure. The discussion was made in detail. Multirange fractal model was proposed to calculate transition region curves of multirange fractals. The results show that values of simulation show good agreement with experimental values, the maximum error is less than 1.3%. From the analysis, the range of the transition region between two fractal regions is speculated to be related with structure properties of metal melts. In addition, ultrafine particles’ aggregation mechanism was used to analyze the fractal morphologies. Keywords: multirange fractal; In-40wt.%Sn melt; microstructure change; X-ray diffraction.

Abstract: Microstructure and mechanical behaviors of AZ91 cast magnesium alloys with melt superheating and thermal rate treatment technique were studied. Alloy grains thicken at 820°C and refine at 870°C when they contains Mn element and the crucible had no coating on the internal surface. Moreover, the strengthening γ phase is more dispersive and uniform at 870°C. Thermal rate treatment significantly improved the microstructure, mechanical behaviors and casting quality of AZ91 alloy as microstructure of AZ91 alloy reserves some characteristics of the high temperature melt.