Efficiency of different commercial TiBAl grain refiners on refinement of pure aluminum cast structures

¹ Physical Metallurgy Group, Advanced Materials Division, Mintek, 200 Malibongwe Drive, Randburg, 2125, South Africa.
² Hulamin Rolled Products Research and Development, Hulamin Operations (Pty) Ltd. Moses Mabhida Road, Edendale, Pietermaritzburg, 3201, South Africa.

Abstract

Industries largely rely on empirical tests to determine what composition and amount of TiBAl grain refiners to add during the casting of aluminum alloy for cast grain structure refinement. TiBAl grain refiners are aluminum master alloys having intermetallic particles within the aluminum matrix, these particles are mainly made of Ti and Al borides, having higher melting point than aluminum matrix. Addition of them to the melt, induces heterogeneous nucleation of aluminum cast grain structures, which promotes solidification of fine equiaxed grains at expense of columnar grain structures. This yields in grain refinement of cast structures, and is beneficial to mechanical and surface treatment properties on the final product. Very often in industrial practice during casting, whether a grain refiner is suitable for a given alloy, the amount to be added in the melt, and what cooling rates to use, are questions remain and reaching the balance becomes a cumbersome practice, and leads to pernicious material’s properties. This study aims to explore the refinement efficiency of three variants of locally supplied TiBAl grain refiners on the microstructure of cast pure aluminum (CPAl). A standard test method of TP-1 was adopted and the efficiency of TiBAl grain refiners was determined according to the average grain sizes. It was found that Al-3Ti-1B alloys from different suppliers yield different grain sizes, however, Al-5Ti-1B alloy has better efficiency than Al-3Ti-1B alloy system on CPAl material. The optimum holding time for CPAl melt at 750℃ is 5 minutes to achieve a fine grain size.