Papers by Keyword: Magnesium Alloy

Abstract: Microstructures of the long period stacking ordered (LPSO) phase deformed by compression test or rolling at room temperature were investigated. The Mg₈₅Ni₆Y₉ (at.%) alloy was composed mostly of plate-type phase with 10H-type LPSO structure. The Mg₈₅Ni₆Y₉ alloy exhibited compression yield stress of 365 MPa and fracture strain of 30 % at room temperature. After compression test with applied stress of 25 %, a bend, delamination between basal planes and crack initiation at boundary of the LPSO phase were observed. From these microstructural features, it was considered that the deformation of the LPSO phase significantly influenced by a kink deformation. The Mg₈₅Ni₆Y₉ alloy could be rolled with 30 % reduction at room temperature. The kink deformation was frequently observed in the LPSO phase of the alloy sheet. The basal plane texture was formed in plane sheet of the alloy sheet. However, it was more difficult to form basal plane texture in the LPSO phase than in the pure-Mg due to introduce the kink deformation. Therefore, it was considered that better rollability of the Mg₈₅Ni₆Y₉ alloy compared with the pure-Mg was brought for the kink deformation.

Abstract: The formability of the magnesium-lithium alloy was examined by multi-stage deep drawing. Long cups of magnesium alloy were formed at ambient temperatures by multi-stage deep drawing processes. In multi-stage deep drawing, the magnesium-lithium alloy sheets were employed and a flat sheet blank is formed into a cylindrical by a punch. Various cups were drawn by exchanging the punch and ringed die. The die was flat in the first stage, and was taper without a blankholder in the subsequent stages. The effects of the ratio of blank diameter to punch diameter and blank thickness on the deep drawability were examined. It was confirmed that the Mg-Li alloy long-cups were successfully formed by a multi-stage deep drawing operation in cold.

Abstract: Microstructural factors that govern the plastic deformation of the long-period stacking ordered (LPSO) phase were clarified. The decrease in length of the long-axis for the plate-like shape of LPSO-phase grains increases the yield stress of the alloy in which basal slip is predominant in deformation. On the other hand, the yield stress tended to increase as the thickness of the plate-like shapes of the grains decreased for the alloy in which the formation of deformation kinks carried the strain.

Abstract: AS is a relatively new series of Magnesium alloys. The microstructure of this alloy can be improved for semisolid processing. The current research is concerned with the microstructure evolution of AS21 under the strain induced melt activated (SIMA) process. For this purpose, the AS21 alloy is cast and compressed 10-40% at 200 °C. The semisolid heat treatment is completed in a carbonate salt bath at different temperatures between 600-620 °C. The microstructure studies show that there is no favourable microstructure evolution between 600-610 °C. At 615 °C fine globular grains are obtained with the most desired mean grain size and sphericity of 67 µm and 81%, respectively. At 620 °C an undesirable coarsening phenomenon occurs that damages the microstructure globularity. SEM micrographs show that in a successful SIMA processing, the Mg₂Si phases are broken into fine particles distributed within the grains and grain boundaries.

Abstract: A way to overcome the low deformability of magnesium alloys at room temperature is toincrease the temperature of forming operations. The stress exponent n, which is known to be a keyparameter in the control of plastic stability, generally decreases when temperature increases.Nevertheless, low n-values are not enough to ensure large capacity of deformation since fracturecan also result from strain induced cavitation. In the present investigation, both the mechanisms ofhigh temperature deformation and damage were studied in selected Mg alloys. Since damage datacan also give information on the deformation mechanisms, the strain induce cavitation behaviourwas mainly studied thanks to X-ray micro tomography which provides 3D information like thecavity shapes or the variation with strain of the number of cavities. Moreover, additionally toconventional post mortem analyses, it was attempted to perform the 3D damage characterisation inin situ conditions, namely directly during high temperature deformation tests.

Abstract: In this study, long period stacking ordered structure (LPSO) type magnesium alloys have been developed. They consist of LPSO phase and α-Mg phase and have excellent mechanical properties at both ambient and elevated temperatures. In the present study, the influence of electromagnetic stir (EMS) on the structure of LPSO type Mg₉₆Zn₂Y₂ (at. %) billets of φ200 mm in diameter was investigated in order to establish the large-scale casting technology of LPSO type Mg alloy. EMS refined the grain size of α-Mg up to approximately 1/3.5, and reduced the size difference between the surface and the center of the billets. By applying EMS, it was found possible to provide large-scale casting billets with fine and homogeneous microstructure.

Abstract: Friction Stir Processing (FSP) has attracted much interest as a tool for refining grain size and achieving high angle boundary misorientation in magnesium alloys. These characteristics have a great influence in key engineered properties such as strength and ductility, which could be markedly improved by means of this technique. The main objective of this work is to study the microstructural modifications produced when FSP is applied to homogenized cast AZ91 and wrought AZ61 magnesium alloys. Several attempts were made for achieving a homogenous microstructure without defects and enhancing the refinement of the grain size in the stir zone. It was revealed that is of great importance to break the initial microstructure, of coarse grains unfavourably oriented for deformation, in order to facilitate the process, particularly in the case of cast AZ91 alloy. It is highlighted that, after breaking up the initial microstructure, is possible to process the material, in subsequent passes, Furthermore, the use of different backing materials as heat sink and a previous heating treatment of the sample were evaluated. Changing the backing plate can improve more the reduction of the grain size during a second pass. Using a copper plate instead of a steel one can promote a refinement up to 700 nm in AZ91 and 1 μm in AZ61. A coolant agent can be used for inhibiting the grain growth causing a little more reduction of the grain size.

Abstract: The developed Mg-based metallic glass shows great potential as implants in biomedical applications instead of crystalline Mg alloys, which may possesses acceptable corrosion properties. In this study, corrosion behaviors of melt-spun amorphous Mg₆₇Zn₂₈Ca₅ ribbons were investigated in physiological saline solution. Electrochemical testing and hydrogen evolution rate indicated that the glassy ribbons obtained at lower wheel speed were more noble with smaller corrosion current, and possessed a comparatively lower corrosion rate in physiological saline solution. Surface morphology analysis revealed that glassy Mg₆₇Zn₂₈Ca₅ ribbons exhibited a strong susceptibility to localized pitting corrosion. A Zn-rich passive layer was formed on the surfaces of the glassy ribbons, indicating that Zn was an effective alloying element to enhance the corrosion resistance of amorphous Mg₆₇Zn₂₈Ca₅ alloys.

Abstract: The curves of true stress-strain of AZ80 Magnesium alloy had been tested with thermal simulation experiment, at the conditions of the experimental temperature being 260°C~ 410°C, and strain-rate being 0.001~ 10s-1, and the deformation degree being 50％. According the Arrhenius equation, a kind of constitutive equation of AZ80 Magnesium alloy which considered the strain had been put forward, and the relative errors between calculation results by the stress-strain model and experiment results are less than 10.5%.

Abstract: The microstructures and phase constituent of as-cast Mg-5Sn-5Zn-xSr (x=0, 0.5, 1, 2) alloys were analyzed by the optical microscopy (OM), the scanning electron microscope (SEM) and the X-ray diffraction (XRD). The results indicate that an addition of 0.5%-2% (mass fraction) Sr to the Mg-5Zn-5Sn alloy not only refines the dendrite arm spacing of -Mg but also results in the formation of MgSnSr phases. Furthermore, it was found that the increase of Sr results in Mg2Sn phase decreasing and MgSnSr phase increasing. While the MgZn phase which is attached with Mg2Sn phase exists in the form of -Mg+MgZn eutectic structure.