The influence of internal chills on the structure and properties of aluminium alloy castings

Many of the drawbacks associated with the production of conventionally cast ingots and castings, such as the presence of pipes, centre-line segregation and columnar grains, can be attributed to the manner and extent of cooling inside the mould cavity and the problems of heat transfer from the centre to the outside of the casting. These result in lowering of the average mechanical properties and the yield of the casting. In the past, the use of external chills to reduce the above defects has had limited effects. This is because the influence of external chills becomes marginal beyond a certain distance. One of the potential methods of overcoming such problems is to employ heat sinks in the form of internal chills. Despite reported work by Russian and Japanese investigators on the use of internal chills, in the form of powder or strip, in iron and steel castings, no detailed information on the use of such chills in aluminium or other non-ferrous alloys is available in the literature.This paper presents deta...