Microstructural and mechanical characterization of a superplastic 6xxx aluminum alloy

A new thermomechanical process has been developed which produced a fine grain structure in an Al–Mg–Si–Cu alloy. The alloy under investigation falls within the composition limits of both 6013 and 6111. The refined microstructure has an average grain diameter of approximately 10 μm and an average aspect ratio near 1.6. Superplasticity was investigated using ambient pressure, uniaxial tensile tests and cone tests with backpressure. The refined material exhibits superplasticity above 500°C. Uniaxial tests indicated a strain rate sensitivity of 0.5 at 540°C, where the elongation reached 375% for a flow stress of 680 psi (4.7 MPa). Cone tests revealed excellent overall formability, and the suppression of cavitation with backpressure. The effects of strain on grain size and porosity were determined.