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A New Method for Melt Refinement of Al Cast Alloys in Sand Casting Process

Ganpat Rai and D B Karunakar
Mechanical and Industrial Engg. Department, Indian Institute of Technology Roorkee, Roorkee - 247667, India

Abstract—Aluminium castings have played an integral role in the industrial growth since their inception during the late 19th century. Their early applications include domestic components, such as cooking utensils, decorative parts, etc. These early applications rapidly expanded to address the requirements of a wide range of engineering specifications, particularly, in automobile and aerospace industries. In the present work, an attempt was made to modify the micro-structure of Al-17.0Si-0.5 mg alloy by adding barium to the melt at 4.0% and 5.0% and the modified melts were cast in sand moulds. The cooling conditions were varied for different experiments. Barium metal additions refined the primary and eutectic silicon phases of Al-17.0Si-0.5 mg alloy through simultaneous refinement of both primary and eutectic silicon morphology. Results clearly indicate that barium metal in varying proportions at faster cooling rate exhibited remarkable refinement over the existing methods of refinement for hyper-eutectic Al-Si alloys. The SEM micrographs of the samples, modified by 4.0% Ba and 5.0% Ba, show that when barium was added to the melt, the morphologies of the primary silicon and eutectic silicon changed from coarse blocky shape / irregular morphology to fine blocky columnar shape with reduced primary silicon size. The quantity of refinement increased with the amount of modifier addition and cooling rate. Appearances of such morphology of silicon in the alloy can be attributed to the crystallization behaviour of silicon that has barium in the form of solid solution. Hardness of the modified samples of Al-17.0Si-0.5 mg-4.0Ba and Al-17.0Si-0.5 mg-5.0Ba increased by 10% and 12% respectively in comparison to an unmodified sample (Al-17Si-0.5 mg). Experiments were also conducted with the combined additions of Barium and Al-5.0Ti-1.0B grain refiner and the results were found to be favourable.

Index Terms—Al-Si alloy, Micro-refinement, Barium addition, Grain refiner addition, Crystallization of silicon, Hardness

Cite: Ganpat Rai and D B Karunakar, "A New Method for Melt Refinement of Al Cast Alloys in Sand Casting Process," International Journal of Mechanical Engineering and Robotics Research, Special Issue, Vol. 1, No. 1, pp. 136-149, January 2014.