Extraordinary Flooding of Aluminum Alloy Castings

Processy litʹâ, 2020, Tom 141, №3, p.3-7

Abstract

Received 26.08.2020

UDC 669.715:788

The content content hydrogen in castings of aluminum alloys depends mainly on its content in the melt before casting. However, you should pay attention to some processes that take place outside the furnace space and are not always controlled. Thus, a significant increase in the hydrogen content is observed when casting in crude sand molds as a result of the interaction of the melt with the wet molding mixture: every 100 mm of the path traveled by the melt in this form, add approximately 0.3 cm3 / 100 g of hydrogen. The gas saturation of the melt with the molding mixture can be equated to moistened asbestos. The intensity of this process increases sharply with the introduction into the melt of the modifier in the form of sodium salts: with the introduction of 3% of the modifier increase the gas content of the casting from 1.9 to 3.5 cm3 / 100 g. Flooding can also occur during the crystallization of the casting. Moreover, curing in a humid atmosphere reduces the density and mechanical properties more than melting in a humid atmosphere. In some cases, this effect is used to eliminate the lack of shrinkage defects such as cracks and weights by spraying water on the relevant areas of the painted mold. Flooding is also not excluded after complete curing of the casting due to the interaction with atmospheric water vapor, for example, during heat treatment. Out-of-furnace flooding of aluminum alloys potentially participates in future hydrogen refining of the metal during remelting. To increase the density and mechanical properties of the cast metal, it is necessary to organize not only accelerated hardening, but also cooling of the hardening casting, especially near the liquidus.