Influence of Annealing Treatments on Microstructure and Mechanical Properties of an Extruded Mg AZ31/Al 7050 Laminate

Abstract

Mg AZ31/Al 7050 laminate was fabricated by co-extrusion directly from the as-cast Mg AZ31 and Al 7050 billets. The influence of annealing temperature and annealing time on microstructure and mechanical behavior of the extruded Mg/Al laminate was systematically studied. Results show that annealing treatments at 250 °C for 3 h or at 350 °C for 3 h do not result in an obvious grain coarsening of Mg layer and cannot remove the heterogeneous structure. Annealing does not vary texture in the Mg layer, a large fraction of <0002>//ND and a small fraction of <0002>//TD, but the intensity of component <0002>//ND weakens to some extent. Lamellar microstructure in the Al layer remains after annealing at 250 °C for 3 h or at 350 °C for 3 h. High fractions of the texture components S and cube exist in the extruded sample, and annealing treatment hardly changes their fractions. Post-annealing treatment will largely reduce yield strength of extruded plate and increase plasticity slightly. The yield strength drops from 302 MPa to 206 MPa after annealing at 250 °C for 3 h and to 141 MPa after annealing at 350 °C for 3 h. The elongation to fracture increases from 1.5% to 5.4% after annealing at 250 °C for 3 h and to 4.8% at 350 °C for 3 h. The corresponding mechanism was discussed.