Effect of Mn/Fe ratio on the microstructure and properties of 6061 sheets obtained by twin-roll cast

Abstract

The effect of the Mn/Fe mass ratio on the microstructure and mechanical properties of vertical twin-roll cast 6061 sheets were investigated. The microstructure and morphology of the iron-rich phase of cast and rolled sheets were investigated using optical microscope, scanning electron microscopy, energy dispersive x-ray spectroscopy and transmission electron microscope. The effect of Mn on the equilibrium phase of 6061 aluminum alloy was analyzed by CALPHAD thermodynamic simulation. In addition, the mechanical properties of 6061 twin-roll cast sheets were tested using tensile tests. The results showed that as the Mn/Fe mass ratio increased, the iron-rich phase at the edge of 6061 twin-roll cast plates gradually transformed from acicular β-Al5FeSi phase to granular α-Al12(FeMn)3Si phase. The core gradually aggregated from a needle-like β-Al5FeSi phase to a star-like Al6(FeMn) phase, and finally to an irregular network and petal-like α-Al15(FeMn)3Si2 phase. When the mass ratio of Mn/Fe was 2.0, the twin-roll cast plates exhibited the best mechanical properties, with a tensile strength, yield strength and elongation of 204.80 MPa, 180.59 MPa and 17.83%, respectively.