Papers by Keyword: Mg-Re Alloy

Abstract: The combined strengthening effect of grain refinement by equal channel angular pressing (ECAP) and aging on a wrought Mg-12Gd-3Y-0.5Zr (mass fraction, %) alloy was investigated. The resulting mechanical properties and microstructures were examined by uniaxial tensile test, optical microscope (OM) and transmission electronic microscope (TEM). It is found that ECAP for 4 passes at 673K followed by aging treatment at 523K for 16h is the optimum condition to strengthen the selected alloy Microstructure analysis reveals that precipitates appear at grain boundaries, accompanies by a few precipitates in grain interior after ECAP and aging treatment. By contrast of as-annealed sample, the strength and elongation were improved which revealed that grain boundaries and precipitation hardening were the main contributor to the high tensile strength of the experimental alloy.

Abstract: Traditionally, Mg-Gd alloys have been strengthened by dispersed precipitates. Several reports are available about Sc addition to Mg alloys for improving a creep resistance. In this research, aging behavior of Mg-Gd, Mg-Sc and Mg-Gd-Sc alloys including the same amount of solute elements were investigated to understand the effect of Sc on microstructures and mechanical properties during aging. Hardness measurement revealed that Sc addition delayed to form precipitate. Close inspection of TEM micrographs, β” phase formed at an initial stage of aging and β’ phase was observed at a peak-aged stage in Mg-Gd and Mg-Gd-Sc alloys. In Mg-Sc alloy, there is no evidence of precipitate formation during aging at 473K.

Abstract: The RE-containing Mg alloys usually have big RE-rich intermetallic compounds distributed along grain boundaries. In this paper, a 3 wt.% RE containing Mg alloy is processed by combination of semi-solid slurry-making with ultrasonic vibration (UV) and squeeze casting. Results show that good semi-solid slurry with fine and spherical primary α-Mg particles can be obtained due to the effects of the cavitation and acoustic streaming induced by UV, and the average particle size and average shape factor are about 30 μm and 0.70 respectively. The RE-rich intermetallic compounds are refined and uniformly distributed along grain boundaries. With the increase of squeeze pressure from 0 MPa to 200 MPa during the casting of semi-solid slurry, the tensile strength and the elongation of the as-cast samples are increased continuously, which reach 182 MPa and 8.4% respectively. The microstructure is also analyzed with SEM, TEM, XRD and EDS, and the phase constitutions of this Mg-RE-Zn-Y-Zr alloy are mainly α-Mg matrix, α-Zr, W phase (Mg₃Zn₂Y₃₎, I phase (Mg₃Zn₆Y) and T phase ((La,Ce)(Mg_1-xZn_x)₁₁). The mechanism of refinement of RE-rich intermetallic compounds is also discussed.

Abstract: Currently, long period stacking/ordered phases (LPSO phases) are known to reinforceMg97Y2Zn1 type Mg-RE alloys. The LPSO phases are composed of a solid solution of Y and Znatoms placed orderly in long periods along the Mg basal plane. Also, an efficient way to strengthena polycrystalline material is to reduce its grain size. This increases the density of grain boundarieswhich impede the flow of dislocations. In many of the LPSO forming solidification processed Mg-RE alloys, the common practice is to solutionize the ingot, quench in warm water, hot extrude andthermally age. While this practice is suitable for obtaining high strength Mg-RE alloys, itconveniently employs the common idea in conventional metallurgy of fine intermetallicstrengthening while refining the grain size to within the micron regime. In this work, an alternativemethod involving boride nanoparticle addition to obtain a selected solidification processed ultrahighstrength (tensile yield strength > 400 MPa) Mg-RE alloy is discussed. Here, LPSO phaserather than fine intermetallic formation while retaining grain size under the micron regime ishighlighted.

Abstract: The magnesium alloy containing rare earth element is known to show good heat resistance. In this study, Mg-Y, Mg-Gd and Mg-Gd-Y alloys including the same total amount of solute elements have been investigated to clarified the effect of the Y atom on age-hardening and precipitation using HRTEM, SAED technique and HRTEM simulation. The diffuse scattering by SAED was obtained in as-quenched condition in all alloys. In the specimen at as-quenched condition, the row contrasts consisted of bright and dark dots lying on the {100}_Mg planes, which were considered to mono-layer were observed by HRTEM.

Abstract: By transmission electron microscopy (TEM) and optical microscopy (OM), the isochronal aging hardening law and microstructure have been studied for the Mg-8Gd-3Y-0.5Zr alloy after cold rolling. During isochronal aging process (heated from room temperature to 500 with the heating rate of 1/min), there are two peak hardness temperature points, which are corresponding to the large number of precipitation of β and β phases, and the peak aging time of the alloy substantially decreased with the increase of deformation reduction. The β phases started to precipitate at temperatures of 145, 134, 127 and 124 in the alloy after cold rolling with the reduction of 0%, 8%, 15% and 22%. The heating rate greatly affected the starting precipitation of metastable phases. β phases started to precipitate at temperatures of 109 and 124 with the reduction of 22% and with the heating rates of 3 /min and 30 /min.

Abstract: The effect of Sm content (2, 4, 6, 8wt.%) on the microstructures and mechanic properties of gravity casting Mg-xSm-0.4Zn-0.3Zr alloys were investigated. The results showed that the cast alloy mainly consists of α-Mg matrix and Mg41Sm5 phase distributed at the grain boundaries, and the amount of the second phase increased with the rise of Sm content. After the solution treatment (T4), the second phase disappeared, however small amount of cuboid-like phase were found inside the grain, and its volume fraction also increases with the rise of Sm content. It is found in the age hardening curves of the alloys at 175, 200, and 225 °C that the alloys with various components almost showed the same trend of age hardening. While the higher the Sm content, the harder the alloy. With the Sm content increases, the yield strength (TYS) of cast alloys (F state) were obviously improved, however the tensile strength (UTS) became lower because of the quick drop of the elongation. The elongations of solid solution (T4) and aging (T6) alloy became lower, while the yield strength and tensile strength increased at first and then decreased. The optimized component is Mg-4Sm-0.4Zn-0.3Zr, which the mechanic properties at T6 state are: TYS=131MPa; UTS=261MPa; δ=6.8%.

Abstract: Mg alloys were increasingly attracting attention as a potential implant biomaterials because that there will be no need for a second surgery. However, the majority of conventional Mg alloys have been developed for automotive components and were not suitable for Mg based implants. In this paper, a new Mg-RE based materials was developed for implant biomaterials, avoiding the negative influences of previous systems. Microstructure, mechanical and corrosion properties were investigated. The result exhibited that the mechanical properties and degradable rate were sufficient to satisfy the requirement of Mg-based implants. Furthermore, the deformability of the alloy was also investigated. The fine stent pipe was prepared by cold-drawing technology. The primitive results demonstrated that this new alloy was an ideal stent materials.

Abstract: HRTEM observation was performed to clarify the early stage of precipitation in Mg-Gd-Y alloy aged at 473 K. The hardness increased with increasing aging time after quenching. The hardness increased slowly at early stage of aging, increased rapidly, and then reached to peak hardness. At as-quenching and the early stage of aging, the weak spots appeared at a half 100_Mg in SAED pattern. The intensity of these weak spots changed to higher with increasing aging time. Monolayers on {100}_Mg planes and β” phase existed at this aging stage. Monolayers, β” phase, the precipitates with five layers corresponding the feature of (020)_β’ plane and β’ phase co-existed after the rapidly increasing of hardness. In the peak aged specimen at 473 K, both of β” and β’ phases co-existed and β’ phase were formed dominantly.

Abstract: High resolution transmission electron microscope (HRTEM) observations were performed to investigate the age hardening precipitates in Mg-Gd-Sc alloys. The maximum hardness of these alloys increased with Gd content. The precipitates with the features of β” phase and β’ phase in Mg-Gd alloy were observed in Mg-15Gd-6.4Sc and Mg-10Gd-6.4Sc alloys. Maximum hardness and number density of precipitate in Mg-15Gd-6.4Sc alloy were higher than that in Mg-10Gd-6.4Sc alloy, and the finer precipitates with higher number of density were contributed to the maximum hardness in Mg-Gd-Sc alloys.