MEASURING THERMOMECHANICAL PROPERTIES OF AA7050 NEAR THE SOLIDUS TEMPERATURE

The flow stress and ultimate tensile stress of the solid-liquid mushy zone of AA7050 were measured at solid fractions greater than 0.9 using a tensile testing procedure modified to capture the non-equilibrium microstructural conditions in castings. Tensile testing was conducted by reheating as-cast AA7050 tensile bars above the equilibrium solidus to produce an interdendritic liquid region. The samples were then cooled to the solidus temperature calculated by either the lever rule or Scheil analysis. The samples were strained at different temperatures during the cooling stage. This method produced much lower stress values than heating the specimen directly to the desired test temperature. Microstructures and fracture surfaces after testing using the modified procedure were compared to those of the original as-cast microstructure, confirming the presence of an interdendritic liquid film during testing.