A novel two-stage reheating process with new alloy design has been developed to improve the microstructure morphology of semi-solid Al-Si casting aluminum alloy for thixoforming. The process consists of first reheating the material to the liquidus temperature, holding for 5 minutes, and then lowering to the predetermined two-stage reheating temperature between 843 -863 K and holding for 10 minutes. The experimentally-obtained grain diameter, roundness, and the amount of liquid trapped within the solid phase were characterized, along with the microstructure obtained using the traditional feedstock reheating process. The Wilcox test (with α=0.05) was then applied to statistically analyze the measured differences in the microstructures obtained using the two different processing routes. It was found that a refined near-spherical structure with uniform globule size, higher sphericity, lower coarsening rate constant, and less entrapped liquid was obtained via the new two-stage reheating process in comparison with the microstructure obtained using the traditional feedstock reheating process.
According to the technical features and maintenance support of Electronic Counter Measures (ECM) equipment, this paper proposes a classification scheme for heterogeneous spares based on fuzzy analytic hierarchy process (FAHP). Firstly, the hierarchical structure of the multi-criteria was established by analyzing the criteria impacting item classification; and then the weight vector of each criterion was calculated using FAHP; furthermore, fuzzy comprehensive evaluation was made to construct the fuzzy classification decision model with a sorting method based on the weight vector of triangular fuzzy number using possibility degree. The research work can provide theoretical basis and data support for decision-making of the equipment support sectors.
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