Effects of casting conditions on AlSi21CuNi hypereutectic alloy structure modified with P/Sr microadditions

Purpose: The study aims to evaluate the influence of selected modification parameters with phosphorus and strontium on the structure of the AlSi21CuNi alloy. Design/methodology/approach: Test smelting was conducted using a metal bath heating temperature of 850°C for 30 minutes. Once the temperature of the liquid metal was reduced to 750°C, the modification procedure was carried out. Casting was carried out using a metal mould at 10, 30 and 60 minutes after the modifiers were introduced into the metal bath. The first smelting involved the application of an AlCuP modifier at 350 ppm P by weight of the alloy. The next three smeltings were carried out by simultaneously introducing AlCuP (180 ppm P) and AlSr modifier (150, 250, 350 ppm Sr) into the metal bath. The last smelting was carried out to obtain samples of unmodified silumin. The smelting was carried out using the same procedure as for the modified alloy, omitting the introduction of modifiers into the metal bath. Findings: The conducted modification treatments were evaluated using qualitative and quantitative analysis methods of the microstructure of samples taken from test castings. The metallographic studies were carried out using a scanning electron microscope (SEM) and computer image analysis software. Research limitations/implications: It has been found that the simultaneous modification, i.e. with phosphorus and strontium additives of primary silicon crystals and refinement of the eutectic, represents a compromise between satisfactory fragmentation of the primary silicon crystals and the degree of refinement of the eutectic. The contact time of the modifiers with the metal bath is an important modification parameter in the given context. Further studies on the complex modification with phosphorus and strontium of other alloys from the group of hypereutectic silumins are justified in order to obtain material properties satisfactory to customers, i.e. manufacturers of various types of products. Practical implications: The simultaneous modification of primary and eutectic silicon into hypereutectic silumins is the key to improving their mechanical properties and wear resistance, which translates into the possibility of producing lightweight components for the automotive industry. Originality/value: The paper presents the results of metallographic studies of the AlSi21CuNi alloy before and after modification treatments in the form of qualitative and quantitative analyses of the microstructure of primary and eutectic silicon.