Papers by Author: Wu Xin Yu

Abstract: In this paper, the commercial AZ91 Mg alloy with mixed rare earth (RE) Y、Gd and Nd has been investigated and effects of RE on die-casting microstructure and properties of die-casting Mg alloy has been also explored. The results indicate that RE can effectively refine the grain size of the alloy and improve inner microstructures transforming the reticular structure of Mg₁₇Al₁₂ phrase into granular or dotlike structure. At the same time, the amount of the compound at crystal boundary is less than that in the alloy without RE. In addition, the mechanical properties of AZ91 Mg alloy with mixed RE has been improved efficiently, and its tensile strength s_b can reach over 260MPa; its elongation δ can also reach over 4.5％. When the amount of mixed RE exceeds 5%, it will form coarse Al-RE compounds, which can low the mechanical properties of Mg alloy.

Abstract: The residual stress in cold rolling could decrease the accuracy of ring parts. Because many factors could cause residual stress, it’s difficult to calculate it theoretically. At present, a measurement method was generally used to study the residual stress. For example, X ray could be used to measure residual stress in rings. Through the measurement of residual stress, it could not only obtain the residual stress level after ring rolling, but also validate the finite element model to predict the residual stress distribution. However, because the ring surface was circle, it needs to cut a plane for X ray measure, and it increases measurement inaccuracy. This method only could be suited for qualitative analysis of residual stress in cold ring rolling, and it is not suitable for quantitative analysis of residual stress distribution.

Abstract: Experiments for a new type of electric discharge machining (EDM) were conducted with the water film dielectric formed by tap water and compressed air. An energy factor E is introduced and employed to estimate unit-area effective power input. The experiments show that the flushing conditions with lower air jet pressure can get lower relative tool wear and higher material removal rate (MRR). Higher discharge current and higher energy factor E obtain the higher MRR in air-aided water EDM with positive polarity tool.