Heat Treating Microstructures of a CuAlZn Shape Memory Alloy

Heat Treating Microstructures of a CuAlZn Shape Memory Alloy Dr. Francisco Ambrozio Filho and Dr Maria do Carmo Amorim silva, and Ms. Eizi Tozaki, Mercedes Bens do Brasil This paper presents heat treating microstructures of a ternary CuZnAl alloy. A nominal alloy composition of Cu-25%Zn-3%Al weight percent was prepared by melting and casting and the determination of the ingot chemical analysis presented almost the same value. Heat treatments of small samples were performed by heating, homogenization at temperatures from 700 to 950 °C and quenching by room temperature water. Room temperature microstructures were analyzed by optical (OM) and scanning electron (SEM) microscopes. All the heat treated samples presented two phases (á and â) at the heated temperatures with a decrease of á for higher temperatures. This result agree with the calculated thermocalc expected â for these temperatures. The region correspondent to â phase presented martensite or widmanstatten á structure depending on the heat treating temperature , consequence of the different â composition. When â phase composition in the heat treating temperature has martensitic transformation temperature above room temperature the â phase transform to martensite, otherwise â changes to widmanstatten á morphology. The â to martensite transformation in the cooling is analysed by considering â composition and cooling speed in the heat treatment. Differential scanning calorimetry (DSC) was performed in the samples with martensite in the microstructure to determine the martensite reversible transformation temperature