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The cooling gradient of Mg–3Zn–1Ca–0.5Sr alloy in cast ingots under different cooling methods (air cooling, warm-water cooling and ice–water-mixture cooling) was examined and the effect of cooling rate on the structure and corrosion properties was studied. The microstructure of the alloy was composed of α-Mg, Ca2Mg6Zn3 and Mg17Sr2 phases. As the solidification cooling rate increased, the grain was refined, Zn and Sr were less segregated, the distributions of Zn and Sr were more uniform, and corrosion rate was found to first increase and then decrease; this contradicts the findings of recent research. With cooling rate increasing, the number of corroded microcouples comprising second phase and α-Mg increases. More α-Mg participates in corrosion, leading to a layered and deep corrosion pit and an increased corrosion rate. However, as the microstructure became sufficiently dense, the corroded structure protected the deep α-Mg from participating in corrosion, thus reducing the corrosion rate. [ABSTRACT FROM AUTHOR]

The extruded Mg–7Y–1Nd–0.5Zr (wt%) alloy were performed to the same strain hot rolling with different temperatures. The microstructure and texture evolution of the sheets were investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and electron back-scattered diffraction (EBSD). The results indicate that the microstructure becomes homogeneous after hot rolling process and precipitated phase distributes at grain boundaries along rolling direction. With the increase in rolling temperature, the grains of sheet grow up. The sheet rolling at 400 °C is composed of recrystallization grains, the necklace of the precipitated phase in the grain boundaries and excessive dislocations. The structure of necklace of the precipitated phase is fcc structure with lattice constant of a = 0.75 nm. With rolling temperatures increasing from 400 to 450 °C, the content of recrystallized grains in volume fraction with relatively random orientations increases significantly. Compared with the rolling process at 400 °C, the amount of precipitated phases is reduced at the grain boundary, and the precipitated phase begins to appear in the grain interior when rolling at 450 °C. The structure of the precipitated phase is fcc with lattice constant of a = 2.22 nm. The recrystallization grains begin to grow in the rolling process at 500 °C. The basal texture is obviously produced during the rolling process at 400 and 450 °C; however, the basal texture is weak in the rolling process at 500 °C. The pole point of the (0002) pole figure is concentrated in the center. It can be seen that the basal surface is parallel to RD–TD surface of the rolling sheets. Compared with as-extruded alloy, the basal texture is significantly enhanced with a small increase in basal texture intensity from 6.127 to 7.175, and (10 1 ¯ 0) and (11 2 ¯ 0) textures change to random textures. [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of Mg–7.0 wt%Y–1.0 wt%Nd–0.5 wt%Zr magnesium alloy were investigated both in as-cast condition and after homogenization heat treatment by differential scanning calorimetry (DSC), optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and hardness measurement. The results indicate that the as-cast alloy consists of α-Mg matrix, Mg24Y5 and Mg41Nd5 phases, which are eutectic phases (cubic Y-rich phase). With the increase in homogenization temperature and time, the Mg24Y5 and Mg41Nd5 phases are completely dissolved into matrix, and only yttrium of intermetallic compounds leaves around boundary. After homogenization heat treatment, the elements distributed uniformly and the grains grow up not obviously, only yttrium element of intermetallic compounds left around boundary. The optimum homogenization condition is at 537 °C for 16 h. The mechanical properties are improved after homogenization, with tensile strength of σb = 181 MPa, yielding strength of σ0.2 = 144 MPa and elongation of δ = 5.5 %, which are better than those of as-cast alloy. [ABSTRACT FROM AUTHOR]

The corrosion behaviors of T5 (225 °C, 6.5 h) and T6 (460 °C, 2 h + 225 °C, 12 h) peak-aged Mg-7Gd-5Y-1Nd-0.5Zr alloys with oxide films were investigated by optical microscope (OM), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The weight loss rates and electrochemical tests were also analyzed. The thicknesses of T5 and T6 oxide films are roughly 0.6 and 1.0 μm, respectively. The components of oxide films mainly consist of O, Mg, Y, Nd, and Gd, and the T6 oxide film results in surfaces with larger peaks than T5 oxide film. In addition, Y, Nd, and Gd peaks are all higher than those of Mg-7Gd-5Y-1Nd-0.5Zr alloys, but Mg peak is consistently far below than that of the alloys. The specimens could be arranged in decreasing order of corrosion rates and corrosion current densities: T6 oxide film < T5 oxide film < T6 without oxide film < T5 without oxide film. The oxide films are compact to increase the corrosion resistance for Mg-7Gd-5Y-1Nd-0.5Zr alloys, which will provide a guiding insight into the corrosion and protection of Mg-RE alloys in atmospheric environments. [ABSTRACT FROM AUTHOR]

By means of optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses, the microstructures of as-cast and heat-treated Mg-4Zn-1Y (wt%) alloy containing quasi-crystal phase were studied. The microstructure of the as-cast alloy consists of α-Mg solid solution grains, intermetallic particles and eutectic phases (W-phase and I-phase), and huge grains with serious dendritic segregation are clearly observed. After heat treatment, phase transformation and dissolution occur in the alloy and many phases remain. When the alloy was treated above 410 °C, the eutectic phases transform into spherical shape as the I-phase turns to W-phase. After heat treatment for long time, the alloy is over burnt and the W-phase decomposes to Mg-Y binary phase. [ABSTRACT FROM AUTHOR]

Mg-Zn-RE (Gd, Y) alloys with different Gd/Y atomic ratios were prepared by conventional casting, and the microstructure of the alloys was studied by multiple means. Icosahedral quasicrystal phases are observed in all alloys. The different Gd/Y atomic ratios affect the microstructures of the alloys irregularly. The alloy with more Gd has large dendritic structure and more complicated phase composition which are composed of I-phase lamellar eutectic, W-phase divorced eutectic, Mg-RE cuboid particles and Mg-Zn binary phases. Other two alloys show similar microstructures and phase compositions with very thin lamellar eutectics which distribute along the interdendritic region, and the lamellar eutectics are formed by I-phase and Mg. The element contents of the I-phases and Mg-RE phases are partially controlled by the Gd/Y atomic ratio. [ABSTRACT FROM AUTHOR]