Microstructure and properties of an AZ61 alloy after extrusion with a forward-backward oscillating die without preheating of the initial billet

We have investigated the microstructure, mechanical and corrosion properties of an AZ61 alloy that was extruded using a newly developed technique with an oscillating die (KoBo). The KoBo method allows the extrusion of AZ61 without preheating of the initial billet at high deformation ratios. The combined SEM, EBSD and TEM investigations of the microstructure revealed significant microstructure refinement as well as changes to the intensity of the texture and the distribution of the Mg17Al12 phase. The size of grains was reduced from coarse (davg 20.4 & mu;m for the initial billet) to fine (davg 6.6 & mu;m for the extrusion ratio of R1 7:1 and davg 4.5 & mu;m for R2 10:1). However, in this study, it does not improve the strength and the corrosion properties of the AZ61 alloys. The continuously precipitated Mg17Al12 phase along the grain boundaries overwhelms the strengthening due to grain refinement. Intense corrosion occurs in the case of the KoBo-extruded samples, and the main mechanism of the corrosion is microgalvanic, taking place between the matrix and the Mg17Al12 formed at grain boundaries.& COPY; 2023 Elsevier B.V. All rights reserved.