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The detrimental effects arising from the presence of an excess of dissolved hydrogen in aluminium are numerous. Hydrogen causes porosity in aluminum products leading to many casting defects, reduced mechanical properties like fatigue and lower corrosion resistance. Several methods are used to reduce
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The closed loop recirculation is a proven method of directly monitoring hydrogen in molten aluminium. A small volume of carrier gas, usually nitrogen, is brought in contact with the melt by means of an immersed probe, and is continuously recirculated in the closed loop until its hydrogen content
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A hydrogen analyzer can be used for direct measurement of hydrogen in liquid aluminium. Direct monitoring of hydrogen is possible using an on-line quantitative measurement technology based on a closed-loop gas recirculation method though a porous ceramic probe.
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An on-line method of measuring hydrogen in aluminum is then required to characterize and optimize the process, which helps ensure the quality of outgoing products and monitors the performance of these degassing processes. Traditional laboratory methods, such as
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Bernd
Prillhofer, Holm Böttcher, Development and Practical Performance Characteristics of a New Impeller for Metal Treatment in Casting/Holding Furnaces, Light Metals 2009, The Minerals, Metals & Materials
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of hydrogen in solid aluminium is much smaller than in liquid aluminium. As the aluminium freezes, some of the hydrogen comes out of solution and forms bubbles, creating porosity in the solid aluminium.
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Hydrogen forms whenever molten aluminium comes into contact with water vapor, and easily dissolves into the melt. The gas tends to come out of the solution and forms bubbles when the melt solidifies.
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concentration in the gas is measured and converted into a reading of the gas concentration in the metal. This method is fast, reproducible, and accurate, and can be used online on the factory floor.
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An example of analyzer for direct hydrogen measurement in liquid aluminium is the
Accurity. It works with a probe immersed in liquid aluminium and it uses the closed-loop recirculation method.
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want to produce high-quality aluminum castings with minimum porosity. Hydrogen porosity can be reduced by reducing the amount of hydrogen in the liquid aluminium alloy, by
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the amount of dissolved hydrogen from the melt, such as furnace fluxing prior to the casting process or using in-line degassing equipment during the casting process.
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Peter D. Waite, IMPROVED METALLURGICAL UNDERSTANDING OF THE ALCAN COMPACT DEGASSER, Light Metals 1998, The
Minerals, Metals and Materials Society, 1998, pp 791-796
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Since its introduction in 1989, this gas recirculation method has been increasingly used by major aluminum producers.
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In Situ
Hydrogen Measurements in Liquid Al-Si foundry Alloys, Florence Paray, McGill University
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in the gas loop of the instrument is determined by a
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235:Accurity Hydrogen Measurement in Liquid Aluminium
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217:Hydrogen Gas Analyser
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325:Metallurgy
314:Categories
272:References
156:Aluminium
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166:sparging
138:hydrogen
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96:May 2010
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