Optimization of Si Content to Inhibit Inhomogeneous Deformation in Al-Mg-Si Alloy Fabricated via Twin-Roll Casting

Abstract

Herein, the effects of Si content on the microstructure evolution of Al-Mg-Si alloys during twin-roll casting (TRC) and subsequent heat treatment were characterized using scanning electron microscopy, emission electron probe micro analysis, electron backscatter diffraction, and transmission electron microscopy. The effects of insoluble Si particles, solute gradient, and recrystallization on the mechanical properties of the alloy in the T4P state were analyzed. An inhomogeneous deformation in the thickness direction of the TRC strip was observed during the pre-strain test. A premature local deformation at the element barren region (EBR) in the middle of the strip was considered to be the origin of the limited mechanical properties. By increasing the Si from 0.7 wt% to 1.1 wt%, the content and uniformity of the solute in the EBR can be effectively improved. The stronger work-hardening ability weakens the inhomogeneous deformation. Si addition significantly increased the number of insoluble Si particles during the heat treatment. The structure with a hard shell and soft core in the TRC strip significantly reduced the negative effect of insoluble Si particles on the mechanical properties. The tensile strength and uniform elongation of the strip increased from 159.44 MPa and 18.36% to 209.96 MPa and 29.791%, respectively.