Effect of initial as-cast microstructure of AZ91D magnesium alloy on its semisolid microstructure
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Dendrite (mathematics)
The influence of withdrawal rate on the microstructure of directionally solidified Mg-x%Zn (x=2, 4, 6) alloys was investigated in this paper. It was found that with the withdrawal rates increased from 20 μm/s to 60 μm/s, the morphology of the solid-liquid interface changed from planer to cellular dendrite. When the growth rate was further increased to 120 μm/s, the solidification microstructure appeared to be the typical dendrite structure with the developed secondary dendrite arms. Meanwhile, the dendrite arm spacing decreased with the increase of growth rate. Under the same solidification conditions, the microstructure went through cell branch transformation with the increase of Zn content within a lower withdrawal rate range; while the Zn content did not affect the morphology at a higher withdrawal rate. As well, the microstructure was refined gradually with the increase of Zn content. The effects of withdrawal rate and alloying content on morphology were analyzed by constitutional supercooling and the MS theory.
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The efficacy of ingot level lifetime testing has been limited due to historically poor correlation between ingot lifetime and cell performance. Studies have shown that the DC photoconductance decay is capable of determining differences in average ingot lifetime as a function of starting material, but those studies showed the effects to be a small portion of the total variation. This work looks at a new attempt to correlate ingot lifetimes and cell performance given a more stable starting material supply, and an overall accounting of the sources of variation contributing to ingot lifetime. Finally, ingots whose lifetime was particularly low relative to the predicted performance were studied leading to an indication of additional root causes. The work, as a whole, provides a perspective on the practical impact of various factors on ingot lifetime.
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The influence of melt superheat treatment on the directional solidification microstructure of Al-4.7%Cu(mass fraction) alloy was studied at 750,850,950 and 1 050 ℃,respectively.The characteristics of the melt were measured by integrated thermal gravimetric analyzer.The results show that the primary dendrite arm spacing of the superheated samples at 950 and 1 050 ℃ decreases 31.2% and 36.2%,respectively,compared with the sample treated at 750 ℃.Along with the increase of melt superheat time,the primary dendrite arm spacing decreases and the microstructure is refined.However,if the melt stays at low temperature for a long time,the primary dendrite arm spacing increases and the microstructure coarsens,which indicates that the effect of melt superheat treatment on the morphology of directional solidification microstructure declines.The radical reason is that the superheat treatment makes the alloy microstructure changed.
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In order to improve ingot structure and to refine grain size of Cu Al Ni shape memory alloys by means of electropulse modification, the effect of voltage, frequency and time of the pulse as well as the type of cooling mold on the macrostructure of ingot have been systematically studied. The results show that the above four parameters are important influencing factors on the ingot macrostructure. By appropriately adjusting the parameters, the macrostructure of polycrystalline Cu Al Ni ingot can be significantly improved and nearly fully equiaxied region of the ingot is obtained; the corresponding grain size of the ingot can be dramatically reduced to less than 1/20 of that of unmodified.
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Abstract By alloy melting, microstructure analysis and micro-hardness test, the effects of Sm addition on the microstructure of Mg-12Gd-2Y-0.5Zr alloy with solution treatment and aging treatment were investigated. The results showed that the microstructure of the tested alloy consisted of α-Mg matrix, Mg 41 Sm 5 , Mg 5 Gdm, Mg 24 Y 5 and β’ phases, and Sm improved the micro-hardness value of α-Mg matrix attributed to its better solid solution strengthening effect in α-Mg. The micro-hardness of the alloy with Sm increases obviously from HV121.4 to HV134.3 when compared with that of Mg-12Gd-2Y-0.5Zr alloy.
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Cu–10% P–6% Sn alloy rods with columnar crystal structure were synthesized in this study utilizing Cu–10% P–6% Sn alloy as the starting material. Continuous directional solidification was used to produce Cu–10% P–6% Sn (mass percentage) alloy rods with a diameter of 8 mm, and the heat treatment procedure was arried out under the condition of cast alloy. Optical microscopy and field emission scanning microscopy were then used to investigate the microstructure of the cast alloy. The impact of heat treatment on microstructure evolution was also investigated. The microstructure of a Cu–10% P–6% Sn alloy produced by continuous directed solidification had a Cu-rich dendritic structure, and the second phase structure was linear or spherical, according to the findings.
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Abstract The effect of Sr addition on the microstructure of a melt-spun Al-12% Si alloy has been investigated using X-ray diffraction and transmission electron microscopy. The Sr addition has no effect on the phase constitution but has a marked effect on the microstructure of the melt-spun alloy. The distribution, morphology and orientation of Si in the melt-spun alloy with the Sr addition are different from those in the alloy without Sr. Under rapid solidification conditions, cooling rates play a dominant role in the microstructure formation of the Al-12% Si alloy.
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AbstractAbstractMacrosegregation in heavy steel ingots was studied through numerical and experimental studies of a 500 kg ingot. The numerical model used heat conduction coupled with thermal convection. Simulation results confirm that a small 500 kg ingot poured in a sand mould has a solidification time that is equal to that of a 10 000 kg industrial ingot cast in an iron mould. Accordingly, the sand moulded ingot exhibits more severe macrosegregation compared to the iron moulded ingot, indicating the possibility that a relatively small ingot in sand can simulate conditions in a much heavier steel ingot in a conventional iron mould. Experiment demonstrated that a 500 kg ingot exhibited all the types of macrosegregation, including A- and V-segregates and negative and positive segregation commonly found in a 65 000 kg steel ingot.Keywords: MACROSEGREGATIONHEAVY STEEL INGOTNUMERICAL SIMULATION
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