Comparative study on performance and microstructure of composite water-soluble salt core material for manufacturing hollow zinc alloy castings

Abstract

The water-soluble salt core material has been successfully used for manufacturing hollow aluminum and magnesium alloy castings. However, there is rare report about the water-soluble salt core being used for lower melting point and higher density hollow zinc alloy castings. In order to obtain a high-performance composite water-soluble salt core material (CWSSC) which is suitable for manufacturing hollow-structure zinc alloy castings via high pressure die casting process, the comparative study on performance and microstructure of the salt cores fabricated by gravity casting technology was investigated using KNO3 and KCl as the base salt material with the reinforcements of bauxite or glass-fiber powder. The results show that CWSSC strengthened by reinforcements possesses many advantages of good surface quality and water-solubility rate, high bending strength and impact toughness, low shrinkage and moisture-absorption rate, and CWSSC composed of KNO3-20 mol% KCl with 15 wt% bauxite powder and 15 wt% glass-fiber powder has the better comprehensive performance, whose surface roughness is 0.4758 μm, bending strength is 46.6 MPa, impact toughness is 21.72 kJ/m2, and water-solubility rate is 178.21 kg/(min·m2) in still water at 80 °C with relatively low shrinkage and 24 h moisture-absorption rate. The scanning electron microscope analysis shows that the strengthening-toughening mechanisms of CWSSC mainly include refinement of the grain and deflection of the crack caused by KCl dendritic crystal and the rigid enhanced powders. A practical casting test has been conducted to prove that the developed CWSSC can be used to manufacture hollow-structure zinc alloy castings.