Effect of low-frequency electromagnetic field on the as-cast microstructure of a new super high strength aluminum alloy by horizontal continuous casting
The super high strength aluminum alloy ingots with 100 mm in diameter were cast by the process of low-frequency electromagnetic horizontal continuous casting (LFEHC) and the effect of electromagnet ic field on the as-cast microstructure was studied. Results show that microstructure of the sample prepared by the LFEHC process was greatly refined. Microstructures at the border and the center of the ingots were fine, uniform and rosette-shaped. Electromagnetic frequency plays a key role in microstructure refining. Fine and uniform microstructures can be obtained with optimal electromagnetic frequency. In this experiment, under a frequency of 30 Hz the microstructure was the finest and the most uniform.
Present research and developing trends of ultra high strength aluminum alloys
Possessing high strength and toughness, ultra high strength aluminum alloy is a kind of structural material with light weight and high strength, which can be applied widely in the aviation and aerospace fields. Based on a tremendous amount of data and some experiments by the researching group, this paper introduces the development and applications of ultra high strength aluminum alloys, and discusses the addition, existential form and functioning mechanism of such compositions as Zn, Mg, Cu and Zr. Comparing and analyzing a number of data, the thesis discusses the microstructural mode corresponding to the best properties. Additionally, three main aging treatments and two successful stress corrosion resistance models are also reviewed in this paper. In the end, aiming at the existing problems of the present study, the paper puts some suggestions for the future exploration of the high strength aluminum alloys.
Evaluation of Quantum II microbiology system for identification of gram-negative bacteria of veterinary origin
The ability of a rapid, semiautomated bacterial identification system, the Quantum II microbiology system (Abbott Laboratories, Irving, Tex.), to accurately identify gram-negative bacteria from veterinary sources was evaluated. A total of 378 isolates were tested, including 298 organisms in the family Enterobacteriaceae and strains representing Acinetobacter sp., Aeromonas sp., Flavobacterium sp., Pasteurella multocida, Plesiomonas sp., and Pseudomonas spp. Of these isolates, 333 (88.1%) were correctly identified, 20 (5.3%) were not identified, 10 (2.6%) were incorrectly identified at the genus level, and 15 (4.0%) were incorrectly identified at the species level. The Quantum II system correctly identified 268 (89.9%) of the isolates of Enterobacteriaceae and 65 (81.3%) of the nonenteric isolates. P. multocida was not identified correctly, and some nonenteric gram-negative bacteria of clinical significance in veterinary medicine are not included in the data base. The Quantum II system provided an accurate identification system for isolates of Enterobacteriaceae but had limited usefulness for the identification of other gram-negative bacteria of clinical significance in veterinary medicine.