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Lijing Lin,Xin Xian,Zhihong Zhong,Yucheng Wu,Peter K. Liaw 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.8
The effect of long-term thermal exposure at 700 °C on the microstructure and mechanical behavior of as-castCrMnFeCoNiAl0.25was investigated. Results indicated that microscopically, the as-cast alloy was not an equilibrium alloyto maintain a single FCC structure after long-term aging. The strip-like sigma phase (Cr-rich σ phase) and B2 phase (NiAl)precipitated in the FCC matrix and coarsened when the exposure time was increased. Due to the increased volume fractionand the strengthening of these precipitates, the yield strength and Vickers hardness increased considerably with increasingthe thermal exposure time up to 2000 h. The yield strength increased from 272 MPa for the as-cast alloy to 993 MPa for thealloy exposed for 2000 h. The hardness increased up to 322 Hv for the alloy exposed for 2000 h. However, the yield strengthdecreased to 664 MPa for the alloy exposed for 4000 h, owing to the coarsening of precipitates. The alloy maintained a goodcompressive plasticity after long-term aging.
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Self-adjusting strategy based on rotating injection for sensorless control of high-power PMSM drives
Xiaofan Wang,Xiaochun Fang,Zhi Wang,Zhihong Zhong,Yizhi Wang,Fei Lin,Zhongping Yang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
As a sensorless control method suitable for permanent magnet synchronous motor (PMSM) at lowspeed, rotating high-frequency injection method will face some special problems in high power applications. On the one hand, the low switching frequency limits the injected signal frequency, which is very close to the fundamental frequency. On the other hand, under heavy load conditions, the fundamental current amplitude is several hundred times of the negative sequence current. This will result in difficulty in signal extraction. In this paper, current spectrum is analyzed quantitatively based on the parameters of PMSM drive for rail vehicles, which illustrates the limitations of conventional bandpass filters. A method based on self-adjusting filter is proposed. The negative sequence current is successfully extracted, and the precise rotor position is obtained under the condition of variable speed and variable load. Based on a fullscale test platform the effectiveness of the proposed method is proved.
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Kuijing Song,Xinquan Liu,Yukai Ji,Yong Wei,Junrui Luo,Fei Liu,Dashuang Liu,Zhihong Zhong 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.4
Aluminum/magnesium (Al/Mg) alloys have good metallurgical compatibility as well as similar melting and recrystallizationtemperatures. Therefore, the formation of deleterious IMCs is considered as a major problem in dissimilar Al/Mgalloys joining. In this paper, the metallurgical reaction behavior and atomic diffusion in Al/Mg solid state joining interfaceare studied. Based on the thermodynamic, kinetic and crystallographic characteristics of ordered phase transformation andatomic diffusion database, a phase field calculation framework of the polycrystalline β–Al3Mg2 and γ–Al12Mg17 evolutionis developed. Diffusivity, D and interface mobility, M, which significant kinetic parameters are defined as alloy compositionsand joining conditions dependent. By a series of simulation, it is proved the simulated interdiffusion microstructuralcharacteristics and element distribution across the joining interface are in coincidence with the corresponding experimentaldata. The thermally activated IMC evolution in diffusion bonding is in thermodynamic equilibrium, while accelerated IMCevolution in friction stir welding results from thermomechanically activated D and M. The present study contributes to theunderstanding of interfacial microstructures evolution in solid state joining of dissimilar alloys.
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