Structure-Property Relationships in Dual-Phase Cu-Al Alloys: Part II. Alloy Behavior

The mechanical behavior of dual-phase Cu-Al alloys was investigated and properties were correlated to the relevant parameters: martensite volume fraction, martensite strength, and dual-phase morphology. The yield strength is markedly influenced by all parameters, being an increasing function of both martensite fraction and strength. With respect to component phases it is established that such function does not follow the law of mixtures. On the other hand, ultimate tensile strength exhibits linear dependence on volume fraction of martensite. On comparing theory with experiment, good agreement was established between true uniform strains calculated according to Mileiko's theory of composites and experimental results. High ductility levels are reachable over a rather broad range of martensite volume fraction. Depending on quench temperature, enhancement of ductility occursvia stress-induced phase transformation of martensite to fcc structure. Macrohardness measurements carried out on dual-phase structures showed linear dependence on martensite volume fraction. The data indicate that macrohardness could be predictedvia linear combination of microhardness of component phases and their volume fractions. Strengthening of dual-phase alloys could be achieved, at practically no loss of ductility, by means of short time annealing. Moreover, remarkable strengthening is attainablevia combinations of cold work and annealing while maintaining useful levels of ductility.