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[en] Full text.Friction Stir Processing (FSP) is a new advanced material processing technique used to refine and homogenize the microstructure of sheet metals. FSP is a solid state processing technique that uses a rapidly rotating non-consumable high strength tool steel pin that extends from a cylindrical shoulder. The rotating pin is forced with a predetermined load into the work piece and moved along with the work pieces, while the rotating pin deforms and stirs the locally heated material. It is a hot working process in which a large amount of deformation is imparted to the sheet. FS processed zone is characterized by dynamic recrystallization which results in grain refinement . this promising emerging process needs further investigations to develop optimum process parameters to produce the desired microstructure. In this work, we present preliminary results on the effects of rotational and translational speeds on grain refinement of AA5052. Under certain processing conditions, sub-micron grain structure was produced using this technique
[en] This paper investigated the effects of melt thermal-rate treatment and Al-3Ti-3B-1Y grain refiner on the microstructure and mechanical properties of hypoeutectic Al-9Si-0.5Mg alloy. The results showed that the grain refining effect of the melt thermal-rate treatment was more remarkable than that of Al-3Ti-3B-1Y grain refiner. After the appropriate melt thermal-rate treatment (MTRT), the microstructure and mechanical properties of alloy were significantly optimized and the α-Al phase changed from dendritic grains to columnar grain. The MTRT technique compound with Al-3Ti-3B-1Y grain refiner could further refine the microstructure. In addition, the change of vacancy concentration induced the morphology change of α-Al phase. The mechanism of the refinement and the toxic effect of Y element were clarified, which provide a reference for developing a new type of Al-Ti-B-RE grain refiner and the melt treatment method. (paper)
[en] The experimental results, thermodynamic equilibrium and kinetic theory of the metal/gas interaction in refractory metals are reviewed. The adsorption and desorption of nitrogen, hydrogen and CO are reversible, whereas those of oxygen are irreversible, with adsorption of an oxygen atom and volatilisation of the metal oxide. Based upon this fact, a new electron beam refining technology is proposed for niobium, consisting of four points: preparation of an electrode by aluminothermic reduction; zone refining in the first melt; kinetic refining in subsequent melts and compact design of the refining plant. Experimental results from a 300 kW pilot plant were in complete agreement with the technology proposed, giving 2.4 times the productivity predicted by the conventional technology. (Author)
[pt]Sao revisados os resultados experimentais, teoria termodinamica de equilibrio e teoria cinetica de interacao metal-gas nos metais refratarios. O processo de absorcao e degaseificacao do nitrogenio, hidrogenio e CO e reversivel, enquanto o do oxigenio e irreversivel, com absorcao do atomo de oxigenio e volatilizacao do oxido metalico. Baseando-se neste fato e proposta uma nova tecnologia de refino de niobio por feixe eletronico a partir de quatro pontos, preparacao de eletrodo reduzido por aluminotermia; refino por zona na primeira fusao; refino cinetico nas fusoes subsequentes; configuracao compacta da instalacao do refino. Resultados experimentais numa instalacao piloto de 300 kW mostraram concordancia completa com a tecnologia proposta, fornecendo produtividade 2,4 vezes maior que a prevista pela tecnologia convencional. (Autor)
[en] The influence of various Fe contents on the grain refinement of commercial purity aluminum was investigated. After commercial purity aluminum melted, given amounts of Al-Fe master alloy were added into the molten in this study. Macroscopic observation indicates that the degree of grain refinement of commercial purity aluminum depends on the additions of Al-Fe master alloy. The case of 0.5 wt%Fe content was founded to be more effective in refining grain of commercial purity aluminum compared to the other Fe contents within the range studied. Basing on scanning electron microscopy analyses grain refining mechanism of Fe was discussed in this research
[en] Highlights: • Combined addition of Al-5Ti-1B ribbon and Zr element achieves a very efficient refining effect on ZA22 alloy. • The refining mechanisms of the grains of ZA22 alloy are discussed in detail. • With the decrease of grain size, the tensile strength, elongation and hardness of ZA22 alloy increase. • With the decrease of grain size, the damping of ZA22 alloy shows different variation patterns at different temperatures. A novel Al-5Ti-1B ribbon was prepared and used as inoculant to refine the grains of Zn-Al eutectoid (ZA22) alloy with the aim to significantly enhance the mechanical properties while remaining the high damping capacity. It was found that compared with the commercial Al-5Ti-1B rod the present ribbon had better refining effect on the ZA22 alloy due to its finer and more uniformly distributed TiB2 and L12-Al3Ti particles formed during rapid cooling process. It has been confirmed that both of the two kinds of particles could act as effective heterogeneous nucleation sites of α-Al phase, and then led to the refinement of α-Al grains. The combined addition of Al-5Ti-1B ribbon and Zr element could achieve the best refining effect because Zr could further promote the heterogeneous nucleation and hinder the growth of α-Al grains. Properties tests illustrated that with the decrease of average grain size, the tensile strength, elongation and hardness of the ZA22 alloy increased obviously because of the fine-grain strengthening and dispersion strengthening effects, while the damping showed different variation patterns within different temperature regions, which has been ascribed to the synthetic effect of two opposite influencing factors.
[en] Summer Lecture Series 2006: Andy Sessler, Berkeley Lab director from 1973 to 1980, sheds light on the Lab's nearly eight-decade history of inventing and refining particle accelerators, which continue to illuminate the nature of the universe.
[en] High-intensity ultrasonic treatment (UT) for grain refinement of magnesium alloys has been investigated using a novel theoretical approach in order to better understand its grain-refining potential and the mechanism of nucleation. The process demonstrated significantly superior grain-refining potency to carbon inoculation for Al-containing magnesium alloys but inferior potency to zirconium for Al-free alloys. Details revealed by applying the theoretical approach to ultrasonic grain refinement provide new clues to understanding the mechanism of grain nucleation by UT
[en] The grain size of as-cast Ti-6Al-4V is reduced by about an order of magnitude from 1700 to 200 μm with an addition of 0.1 wt.% boron. A much weaker dependence of reduction in grain size is obtained for boron additions from >0.1% to 1.0%. Similar trends were observed in boron-modified as-cast Ti-6Al-2Sn-4Zr-2Mo-0.1Si
[en] The problems associated with boride agglomeration and the poisoning effect of Zr in Zr-bearing alloys have created a big demand for boron-free grain refiners. The potential benefits of TiC as a direct nucleant for aluminium grains have thus generated a great deal of interest in TiC-bearing alloys in recent years. In Al-Ti-C grain refiners commercially available today, Al3Ti particles are introduced into the melt along with the TiC particles. Since the latter are claimed to nucleate α-Al directly, it is of great technological interest to see if reducing the Ti:C ratio further, i.e., increasing the C content of the grain refiner, will produce an increase in the grain refining efficiency of these alloys. A series of grain refiner samples with the Ti concentration fixed at 3% and a range of C contents between 0 and 0.75 were obtained by appropriately mixing an experimental Al-3Ti-0.75C alloy with Al-10Ti alloy and commercial purity aluminium. The grain refining efficiency of these grain refiners was assessed to investigate the role of the insoluble TiC and the soluble Al3Ti particles. The optimum chemistry for the Al-Ti-C grain refiners was also identified
[en] The commercial thin sheet has a low plasticity and anisotropy in mechanical properties due to the hardening phenomenon in the roll forming process. Using the rolled thin sheet, the manufacturing of the micro-size parts is easy to cause poor formability and poor forming quality. A repetitive roll-bending and straightening (RRBS) method suitable for micro-size materials is proposed, and RRBS based severe plastic deformation and recrystallization annealing of pure copper sheets are investigated experimentally for improving its micro forming formability. With the increase of the pass number of RRBS, the work hardening phenomenon is serious, and the hardness of the material increases. At the same time, the inhomogeneity factor (IF) value decreases as the number of RRBS passes increases, which improves deformation uniformity of the material. The grain size of the sample deformed by the 20 RRBS passes and annealed at 400 °C for 60 min is approximately 17 μm. The investigation in this paper provides a guideline for a potential grain refining process of the rolled thin sheets/foils metal as a blank directly used for micro-forming. (paper)