Existing Ideals about the Influence of Hydrogen on the Properties of Aluminum Alloys. Report 2

• Main Author: F. M. Korlyarskiy
• Format: Article
• Language: English
• Published: PH «Akademperiodyka» 2020-03-01
• Series: Процессы литья
• Subjects: aluminum alloys; casting; hydrogen; dual influence; modifier; refining
• Online Access: https://plit-periodical.com.ua/en/arhiv/existing-ideals-about-influence-hydrogen-properties-aluminum-alloys-report-2
• ISSN: 0235-5884; 2707-1626

The presented literature review chronologically describes the development of the double influence of hydrogen on the formation and quality of castings of aluminum alloys and, accordingly, the ambiguous treatment of it by scientists and foundry men. Until the middle of the last century, there was a unanimous opinion that hydrogen is a very harmful impurity, the cause of various types of defects, a decrease in the yield of suitable and worsening economic indicators of production, so it is necessary to minimize its content in ingots and shaped castings. However, studies carried out in the following years have shown that the use of dissolved hydrogen in aluminum alloys as an alloying or modifying element can significantly strengthen a number of alloys in the deformed state while maintaining a satisfactory plasticity, for the first time to provide the possibility of cold plastic deformation of eutectic silumin. Hydrogen plays a particularly important role in the formation of complex shaped castings with parts, the feeding of which with melt, in order to eliminate concentrated shells and weights, requires an increase in the number of overlaps, technological overlaps and slopes with high unproductive costs of liquid metal, which is not economically profitable. At the same time, increasing the content of hydrogen in the melt allows you to replace the malignant shrinkage defects with a permissible dispersed gas microporosity, keeping the configuration of the casting close to the parts drawing and improving the tightness of metal-intensive units. In addition, the generally recognized positive effect of hydrogen porosity on increasing fracture toughness and reducing heat brittleness. The mechanical properties remain at the level of operational requirements. In practical terms, hydrogen refining of aluminum alloys deserves attention as the cheapest environmentally friendly refining method which, unlike other methods, provides for the selective removal of the largest fraction of solid inclusions, leaving small ones to play the role of nuclo crystals. In this method, the melting of pre-flooded charge materials is transformed from a traditionally polluting melt into a refinery. The review includes the latest developments of the PTIMA of the NAS of Ukraine, which first answered the question: if in some organizations (VILS, MATI) bubbling melt water treatment is used for contamination (for research purposes) by Al2O3 inclusions, and in others (PTIMA of the NAS of Ukraine) using the same operation selectively remove the largest fraction of the same inclusions, so what really happens?; mechanism for replacement of gas porosity by shrinkage at autoclave and low-pressure casting is disclosed; the properties of porous metal are studied, which is important for the evaluation of the operational state of metal capacitive nodes of castings with a porous structure; cases of local leakage in the gas porosity zone; hydrogen porosity - an indicator of the content in the melt of Al2O3 inclusions with the possibility of using the results of the analysis in the course of melting; hydrogen as part of the liquid state structure; combining flooding with other types of melt treatment.