Hot-tearing in Aluminium Copper Alloys

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Abstract
An experimental technique has been developed to investigate hot tearing. In this technique either the load or strain built up during casting could be measured as a function of the mould wall temperature. Experiments were carried out in Al—Cu alloys. Although there was considerable scatter in the results, it was concluded that strength began to build up in the casting when either the liquid volume fraction reached about 4% or when the eutectic temperature was reached. It was also concluded that the initial crack or hot tear occurred in a thin film of liquid or in the solid just below the eutectic temperature. It is suggested that the crack occurs in the liquid when the alloy composition is less than the most susceptible hot tearing composition and in the solid for higher compositions. The crack occurs in the liquid when the liquid volume fraction reaches about 2%. A numerical analysis was made of the heat flow in the casting so that corrections could be made to the thermocouple readings and a technique was developed to calculate the heat transfer coefficient from temperatures measured near the mould wall.

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