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2 2024

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Research of Hybrid Aluminium Castings with the Use of Porous Cores

Brůna M., Medňanský Martin, Oslanec P.

Archives of Foundry Engineering

2024

Vol. 24, iss. 3

18--24

The paper focuses on the research of hybrid aluminium castings produced by overcasting technology. This is an advanced technology for ensuring the lightness of castings by using the principle of overcasting a core with a porous cellular structure produced by foaming. Process parameters in the foaming phase of the material have a great influence on the resulting porous structure. The article focuses on controlling the influence of pressure during the foaming process on the resulting porosity and evaluating by X-ray tomograph and measuring the relative density. Variants using an initial pressure of 0.3 MPa appear to be the most satisfactory. The challenge of this technology is to ensure adequate bonding of the metals at the interface between the porous core and the solidified metal without penetrating the coating layer. For this reason, the surface treatment of foamed cores with various etchants has been proposed to disrupt the oxide layer on their surface. Macrographs of the uncoated sample and samples etched with 0.5% HF and 10% H3PO4 demonstrated the need for core surface treatment to prevent liquid metal penetration. EDX analysis confirmed the presence of AlPO4 at the core/casting interface in the treated sample.

Effect of Core Temperature at HPDC on the Internal Quality of the Casting

Matejka Marek, Bolibruchová D., Podprocká R., Oslanec P.

Archives of Foundry Engineering

2024

Vol. 24, iss. 3

81--87

High pressure die casting (HPDC) is one of the most productive casting methods to produce a wide range of aluminum components with high dimensional accuracy and complex geometries. The process parameters of high-pressure casting generally directly affect the resulting quality of the castings, such as the presence of pores in the casting or the microstructure. In addition to air entrapment, porosity can also be caused by the dissolution of hydrogen. Hydrogen is released by the reaction of water vapor and melt at high temperatures and is released during solidification. These defects can lead to a significant reduction in mechanical properties such as strength and ductility and especially fatigue properties. The aim of the presented article is to describe the effect of the temperature of the core of the high-pressure mold on the presence and distribution of porosity and the microstructure of the aluminum casting in two geometric variants. The temperature of the core was changed due to the use of two flowing media in the thermoregulation circuit of the core, i.e. demineralized water and heat transfer oil and worked with a core temperature of 130 ± 5 and 165 ± 5 °C. With both geometric variants, a higher porosity was achieved when using water (core temperature 130 ± 5 °C) than when using oil (core temperature 165 ± 5 °C). The opposite results were observed for microporosity, where higher microporosity was observed for tempering oil. The microstructure of the casting with water-cooled cores was more characterized by finer grains of phase α (Al) and eutectic Si. In tempering oil, the microstructure was characterized by coarse grains of the α phase (Al) and the Si lamellae were in the form of sharp-edged formations.