Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Physics of metals > The liquid structure of the metal and solidification theory

Metal melt structure changes with temperature regularity of time lag

Author WeiChaoFeng
Tutor JianZengYun
School Xi'an University of Technology
Course Materials Processing Engineering
Keywords Melt structure Resistivity Nucleation undercooling Gallium Al-Si alloy
CLC TG111.4
Type Master's thesis
Year 2008
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Preparation of many materials contain liquid - solid transition, as the parent structure and properties of the liquid phase formed on the microstructure and properties of solid materials have a major impact. Although it is the structure of liquid metal melt a lot of experimental and theoretical studies, however, focused on domestic and foreign research melt at a certain temperature the structure and function of temperature, and there was no change in temperature after its structural variation with time study. This paper studies the melt temperature changes, the resistivity, nucleation undercooling and solidified the variation with time. The main results obtained are: a four-electrode method for continuous non-continuous heating and cooling down after a mild heat and cold resistance of liquid gallium were determined. The results showed that after a temperature change of the resistivity of the liquid gallium with the holding time and change. Fast temperature rise, the resistivity of the liquid gallium with increasing holding time, lowering the temperature quickly, the resistivity of the liquid gallium with the holding time decreases. This shows changes in the structure of gallium melt delay its temperature. The lag time than 20 minutes. Heating and cooling in a continuous process, the liquid gallium at the same temperature in the heating process is less than the resistivity of the resistance of the cooling process, after which the temperature quickly becomes liquid gallium resistivity variation with time is the same. First discovered gallium melt resistivity changes with temperature around the melting point temperature of a discontinuity. Heating process, the cold resistance of gallium melt near the melting point of gallium has a mutation. Continuous heating, the time required to complete mutation about 6 minutes; rapid heating, the time required for complete mutation about 7 minutes. After cooling to overheating gallium melt below its melting temperature, its resistance mutation there is a very significant lag, gallium melt resistivity mutated start lag time over 67 minutes, the melt resistivity gallium used mutated The time is 7 minutes. By DSC thermal analysis techniques were studied after cooling the overheated gallium melt holding time and nucleation undercooling and the exothermic peak area relationship. It was found that gallium nucleation undercooling and cooling the exothermic peak area increased with the holding time after the decrease, which is the gallium melt resistivity is consistent with experimental results. Established to predict the size of the liquid metal atoms theoretical model. According to this model to determine the maximum liquid metal atomic group size and temperature. From the model predicted the maximum liquid Ga atoms size variation with temperature in accordance with the resistivity, the undercooling latent heat of crystallization experiments with temperature variation law. The effects of melt heating temperature and holding time on Al-11.6% Si alloy microstructure and properties. The results showed that: the liquid alloy heating temperature and holding time not only affects the solidification of tissue, but also affects its mechanical properties. The alloy liquid temperature rose from 720 ℃ 900 ℃, the coarse eutectic silicon dots or flakiness into short rod, alloy tensile strength increased 6.33%, 10.83% elongation increases. After heating holding time on microstructures and mechanical properties of different cooling time after the holding time, with the temperature holding time after, Alloy thinning, tensile strength and elongation increase; with holding time after cooling extension, Alloy thicker, lower tensile strength and elongation.

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