The main problem during the production of castings from aluminium alloys is the presence of the reoxidation, which negatively affects the final casting quality. Liquid metal surface reacts with the surrounding atmosphere and oxide layer of Al2O3 is formed on its surface. The problem occurs when the oxide layer is entrained to the internal volume of the melt by turbulence and double oxide layers are formed, also known as “bifilms”. Its formation is related to the melt velocity and gating system design. In paper, naturally pressurized gating system was calculated and designed. Effect of the filter media and vortex element on the melt velocity, amount of oxides, mechanical properties, and porosity were observed. Designs with 10 ppi and 20 ppi foam filters and vortex element were compared with design without filters to prove the positive (or negative) effect of filter media on melt velocity and thus on final casting quality. The melt velocity and amount of oxides were observed with the aid of simulation software. Mechanical properties, quantity of pores, bifilm index and EDX analysis were evaluated after experimental casts. It was proven that by using 20 ppi foam filter in combination with vortex element, the best results were achieved.

An oxide layer is formed on the surface of a molten aluminium alloy when it is exposed to the surrounding atmosphere. The oxide layer on the surface of the melt is not harmful. The problem occurs when it is entrained into the melt volume and solidifies in the casting. The paper deals with the formation of the oxide layer, its types and the formation of a double oxide layers.

Reoxidation is one of the main problem accompanying the aluminium alloy casting process. The oxide layer created on the melt surface during reoxidation is entrained into the bulk of liquid metal and “bifilms” are created. Bifilms have negative impact on cast quality and internal homogenity of final casting. Paper aim is to clarify the reoxidation phenomenon by visualization with the aid of ProCAST numerical simulation software. Experiemtnal work deals with the design of several types of gating systems (non pressurized and naturally pressurized) with vortex elements in order to determine how these elements affect the reoxidation processes. Achieved results clearly confirmed the positive effect of the naturally pressurized gating system with vortex elements. The evaluation focuses mainly on melt velocity and amount of oxides created in gating system and in mold cavity.

Surface of aluminium alloy melt is covered by an oxide layer when it is in contact with the surrounding atmosphere. When the oxide layer is retained on the surface of the melt it prevents the melt by hydrogen saturation. The oxide layer is harmful when it is submerged into the melt. The work focuses on the influence of the melt velocity on the bifilm formation, morphology of oxide layers and their influence on the porosity and filling the mold cavity.