Effect of Mould Coating on Skin Formation and Nodule Characteristics of Thin Wall Ductile Iron Casting

Abstract

Thin wall ductile iron (TWDI) has the potential alternative for lightweight aluminium use in automotive parts. The main problem in TWDI, however, is the formation of skin during the casting, which may reduce its mechanical properties. This casting skin is formed by the decomposition of nodular graphite at the mould interface during the casting process. One of the ways to work around this problem is by using mould coating to control the cooling process. In this work, three variables of mould coatings were used, i.e. graphite, MgO, and MgO/graphite double layers. The results showed that the average casting skin thickness in double layer coating was the lowest (30.41 μm), 57% lower than that of in MgO (71.46 μm) and 60% lower than that of graphite (74.44 μm). The reduction of casting skin thickness increased the mechanical properties of TWDI (346 MPa), 69% higher than that of MgO (223 MPa) and 26% higher than that of graphite (297 MPa). The same is true for ductility (2.7%), which was higher than that of MgO (1.43%) and that of graphite (1.43%).