Ductile Aluminium Cast Irons

Abstract

The authors demonstrate how they developed spheroidisation and inoculation treatments for ductile Al cast iron and subsequently examined the microstructure and tensile properties in the as-cast and normalised conditions at 2.2 and 3.2% of Al. The results show that the sequence of spheroidisation of ductile Al iron differs significantly from that observed in ductile Si iron. Whilst the treatment to introduce some Mg into the melt is required in both irons to alter the growth habit of graphite from flake to spheroidal, the behaviour of the irons towards the subsequent inoculation with various inoculating alloys is quite different. A wide range of mechanical properties in ductile Al irons can be obtained, similar to ductile Si irons, in the as-cast or heat treated conditions. In the as-cast condition, the tensile strength, proof stress and hardness decreased with an increasing Al content, whilst the elongation increased sharply. The tensile properties and hardness values of as-cast ductile Al cast iron were found to be greater than those of ductile iron of equivalent composition. Normalising had a relatively marked effect on the tensile properties at the lower level of aluminium, but most of these properties improved further at the higher level. Microstructural examination showed that the observed changes in properties correlated well with the corresponding changes in the microstructure.