Compositionally complex alloys with the aim of light weight, high strength and high ductility were developed as medium entropy ones using four elements, Cu, Al, Zn and Mg. In order to investigate possibility of improving ductility of the alloys, high temperature deformation and subsequent properties were examined in Cu4Al4ZnMg (4411) alloy with the highest compressive strength at room temperature and the fundamental composition CuAlZnMg (1111) alloy. Flow stress had a peak immediately after yield point and decreased gradually with strain in true stress –true strain curve in both alloys. It was found that cracks at the apex of the indentation in the Vickers hardness test, which showed brittle, were also observed in the specimens subjected to high temperature compressive test at various temperatures and strain rates as well as as–cast alloys before the test. Higher fracture toughness was, however, obtained in the specimens after the compressive test compared with ones before in both alloys. This fact suggested desirable possibility of improving ductility by controlling the microstructure through deformation at elevated temperatures.
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