Hu Guangshan

Neodymium-based Conversion Coating on AZ31 Magnesium Alloy

Abstract A neodymium-based (Nd-based) conversion coating was obtained on the surface of AZ31 magnesium alloy. The formation process of the Nd-based conversion coating was examined by a weighing experiment and an open circuit potential (OCP) test. The coating morphology, microstructure and composition were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The variation of morphology for the bare sample and the coated sample immersed in 3.5 wt% NaCl aqueous solution was investigated. The results show that the Nd-based conversion coating can effectively reduce the corrosion speed in 3.5 wt% NaCl aqueous solution. The composition and corrosion resistance of Nd-based conversion coating after post-treatment were measured by XRD and electrochemical experiments. The post-treatment can perfectly improve the corrosion resistance of the Nd-based conversion coating.

Microstructures and Elevated Temperature Mechanical Properties of As-extruded ZM61-Sn Alloys

Abstract Microstructures, elevated temperature mechanical properties and fracture mechanisms of the as-extruded ZM61- x Sn ( x =2, 4, 8, wt%) alloys were investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and high temperature tensile tests. The results reveal that the addition of Sn can refine microstructures and the refinement effect increases with the increase of Sn content. The average grain sizes of the as-extruded ZM61- x Sn ( x =2, 4, 8) alloys are 11, 8 and 4 μm, respectively. With the increasing of Sn amount, the strength of experimental alloys increases at first and decreases afterward. ZM61-4Sn alloy shows the highest strength, whose ultimate tensile strength and yield strength are 216 and 173 MPa tested at 180 °C, respectively. The ductility increases with the content of Sn increasing, and the elongation of as-extruded ZM61- x Sn ( x =2, 4, 8) alloys are 183.8%, 235.8% and 258.6%, respectively, when tensile temperature reaches 300 °C. The ZM61-4Sn alloy has the optimal coalescence of strength and ductility. The localized necking leads to the final fracture of the specimens and the micro-void coalescence is the main fracture mechanism. Incomplete dynamic recrystallization occurs when tensile tests are carried out at 260 and 300 °C.

Effect of Extrusion Temperatures on Microstructures and Mechanical Properties of Mg-6Zn-1Mn-4Sn-0.5Y Alloy

Abstract The microstructural evolution and the mechanical properties of Mg-6Zn-1Mn-4Sn-0.5Y wrought alloy extruded at 360 and 420 °C were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back scattered diffraction (EBSD) and tensile test. The results show that the phase compositions of as-cast and extruded alloys consist of α-Mg, Mn, Mg7Zn3, Mg2Sn, and MgSnY phases. As the extrusion temperature increases from 360 °C to 420 °C, dynamic recrystallization completes and grain growth occurs. The yield strength, the ultimate tensile strength and the elongation decrease from 259 MPa, 350 MPa and 18.3% to 239 MPa, 332 MPa and 12.5%, respectively. The theoretical calculations combined with the experimental results reveal that fine grain strengthening and solid solution strengthening play the dominating role in the enhancement of yield strength.