Design of mechanical properties of a Zn27Al alloy based on microstructure dendritic array spacing

The present work focuses on the influence of the as-cast dendritic microstructure of a ZA27 alloy (Zn–27 wt%Al) on tensile mechanical properties. A low carbon steel chill was used in a unidirectional solidification experimental set-up in order to permit a wide range of dendritic spacings to be obtained along the casting. Experimental results include transient metal/mold heat transfer coefficients (hi), tip growth rate (VL), secondary dendrite arm spacing (λ2), ultimate tensile strength (σU) and yield strength (σy) as a function of solidification conditions imposed by the metal/mold system. Experimental laws relating σU and σy with secondary dendrite arm spacing are proposed. It was found that both tensile properties increase with decreasing λ2. A predictive theoretical dendritic growth model has been compared with the present experimental observations. Expressions correlating tensile properties, dendritic spacing and solidification thermal variables have been established. Such expressions permit the control of as-cast microstructures by manipulating casting variables, such as the cooling rate and the tip growth rate and can be used as an alternative way to design mechanical properties.