Effect of modification by titanium aluminide powder on the structure of aluminum castings

Purpose. Validation of proposed based on the results of computer model recommendations for modification of aluminium castings by TiAl powder and study of its effect on the characteristics of the metal structure. Methodology. Casting material is technical aluminium which contains 0,3...0,4% Mn, 0,1...0,2% Cu and less than 0,1% Si and Fe. A pre-refined processing of manganese chloride MnCl2 was performed. For modifier input capsules filled with powder including TiAl - 57%, Al powder - 29% and MnCl2 - 14% were used. Fractional composition of TiAl powder was corresponding to the parameters of the lognormal distribution ^ = 0,90 and c = 0,47. The metal processing temperature was 7 5 0 .7 6 0 ° C. Consumption of TiAl was 0,4 g/kg. Methods: Quantitative optical metallography, measurement of the Vickers hardness. Findings. By modifying the decrease in the average crosssectional areas of macro-grains in sections 6...8 times has been achieved. That corresponds to the average linear size reduction by 2.5...2.8 times. Columnar grains were eliminated. Globularization of microstructure was achieved. Approaching of the microstructure grains shape to equiaxed in the modified metal is accompanied by a decrease in the average area of their cross sections in the plane of the sample section. Microstructure refinement is most manifested in the peripheral zone and the half radius area of the casting is approximately 4x (sectional area). Structure refinement leads to an increase in their hardness up to 23.5%. Originality. It was found that the distribution of the grain size of the microstructure for both experimental and comparative castings described as lognormal, but modification significantly affects the parameters c but rather slightly to It is shown that the conditional characteristic shape of the grains in the microstructure of the unmodified casting tends to be rectangular; in modified it approaches the elliptical (centre) and rhombic (the periphery). Practical value. The effectiveness of the theoretically proposed recommendations for modification of small swiftly cooled aluminium castings was confirmed. Achieved results can significantly improve either quality of cast products from technical aluminium or technological properties of cast billets for further shaping