Effect of Grain Refining on the Shrinkage Porosity in Thin-Walled Plates Produced by Investment Casting Integrating Controlled Solidification Technique

Advance Materials and Engineering, CSIR, Pretoria, South Africa.

^* Corresponding author: fsishuba@csir.co.za

Abstract

The production of high integrity thin-walled investment cast components can be achieved by controlling the solidification process. The aim of this work was to study the effect of grain refiner on thin-walled aluminum alloy A356.0 plates produced by investment casting using a controlled solidification process. Moulds with plate thicknesses of 0.7 mm, 1.5 mm and 2 mm were cast. The A356.0 alloy was melted in an electric resistance furnace, one mould was cast with controlled solidification process, second mould was cast using A356.0 modified with Strontium (Sr) (0.03%), grain refiner Aluminium Titanium Boron (Al-5Ti-B) (0.11%) and controlled solidification process. Melt temperature was stabilized at 700°C before being poured into the mould at 740°C. Moulds were inserted into a cooling medium at a controlled rate until the plates were submerged and held submerged for few minutes before being withdrawn. The microstructure and shrinkage porosity were assessed using optical microscope and the density was measured using the Archimedes principle. Qualitative assessment of the shrinkage porosity was measured using Image J software. Grain refinement was shown to reduce the size of primary dendrites. Shrinkage porosity decreased in samples. This was supported by the higher density observed for the grain refined casting.