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Hydrogen gas porosity is an aluminium casting defect under the form of a porosity or void in an aluminium casting caused by a high level of hydrogen gas (H2) dissolved in the aluminium at liquid phase. Because the solubility of hydrogen in solid aluminium is much smaller than in liquid aluminium, when the aluminium freezes, the dissolved hydrogen gas creates porosity in solid aluminium. Aluminum smelters and aluminum foundries want to produce high quality aluminum and shape castings with minimum porosity. This can be obtained by reducing the amount of hydrogen in the liquid aluminium alloy. ==The hydrogen problem== 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. 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 the amount of dissolved hydrogen from the melt, such as furnace fluxing prior to the casting process or using in-line degasing equipment〔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 Society〕 during the casting process. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hydrogen gas porosity」の詳細全文を読む スポンサード リンク
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