| Summary: | The effects of heat treatment on the microstructure, mechanical properties and electrochemical property of the as-extruded Mg-5Zn-1Mn (ZM51) alloy tube are investigated by optical microstructure (OM), X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electrical microscope (TEM), uniaxial tensile test, and electrochemical test. The results show that the as-cast structure is a typical dendritic structure, mainly composed of α-Mg and Mg<sub>7</sub>Zn<sub>3</sub> eutectic compounds. After homogenization, most of Mg<sub>7</sub>Zn<sub>3</sub> eutectic phases are dissolved in the Mg matrix. During the extrusion process, the ZM51 alloy has undergone complete dynamic recrystallization and has a good elongation, reaching 21.4%. T6, especially T4 + double aging treatment, can significantly improve the mechanical properties of the as-extruded tube. The microstructure reveals that the precipitation strengthening of the finely dispersed MgZn<sub>2 </sub>precipitates is the main reason for the strength increase. The fracture micromorphology of the as-extruded tube is mainly composed of dimples and cleavage facets, which is a typical ductile fracture. The fracture mode of the as-aged alloy tubes belongs to cleavage fracture. In addition, the electrochemical test results show the solution-treated ZM51 alloy tube has the best corrosion resistance. The improvement of corrosion resistance is mainly due to the microstructure uniformity and low phase volume fraction.
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