Development of a New Hot-cracking Test for Aluminium Alloys

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Abstract
A new hot-cracking test has been developed for aluminium alloys which allows investigations of hot-tearing to be carried out under well-controlled solidification conditions. The stress which develops in the solidifying ingot is perpendicular to the macroscopic growth direction and so columnar structures are tested normal to the growth axis of the columnar grains. A localised hot-spot must be imposed on the system if a macroscopic hot-tear is to form. Temperatures were recorded at various locations in the solidifying ingot so that the build-up of fraction solid could be monitored. The hot-cracking susceptibility of Al-Cu alloys has been investigated as a function of alloy composition and maximum susceptibility occurred in the range 0.5–2.0 wt% Cu. At a fixed composition of 6 wt% Cu, the grain structure/type was found to greatly influence cracking susceptibility as measured by this test. Hot-tears were always intergranular.