Papers by Keyword: Wrought Magnesium Alloy

Abstract: The traditional extrusion and thixo-extrusion processes of wrought magnesium alloy were studied with both computer numerical simulation and experimental methods. The thixo-extrusion set-up was made. The constitutive model of semi-solid AZ61 alloy was established in our prior literature. The comparison of two forming processes had been done. Results indicated that smaller load and uniform strain & stress were acquired in thixo-extrusion process. Simulation results were in good agreement with experimental ones.

Abstract: The fatigue performance of one widely used wrought magnesium alloy AZ31B in rolled form was studied using acoustic emission (AE). AE energy release during corrosion fatigue (CF) testing was measured at room temperature. It is found that AE energy release can express corrosion fatigue damage experienced by the material.

Abstract: In Mg-Al-Zn and Mg-Al-Mn alloys containing 2.0~6.0mass%Al and 0~1.5mass%Zn, grain refinement in the as-rolled (F) specimens containing large amount of Al and Zn are achieved by both dynamic recrystallization and dynamic precipitation during hot rolling and leads to high strength and high ductility at room temperature. At high temperatures, the tensile strength of the investigated alloys is almost the same, while the elongation of the F-specimens increases with increasing Al and Zn contents, leading to 150% in Mg-4.5%Al-1.5%Zn alloy. High Al and Zn contents alloys significantly accumulate large working strain in grain interiors, and involve large amounts of high angle grain boundaries and fine spherical precipitates, which can become the nucleation sites for recrystallization. Therefore, dynamic recrystallization in such alloys occurs at small strain region during tensile test. This dynamic recrystallization causes reduction of flow stress and large elongation by grain boundary sliding at high temperatures. Furthermore, .fine recrystallized grains contributes to deformation in normal direction, resulting in isotropic deformation behavior. Authors attempt to improve proof stress and its anisotropic property of Mg-Al-Zn wrought alloys by grain size and precipitates controls utilizing dynamic recrystallization and dynamic precipitation during hot extrusion. In the alloy specimens extruded at lower temperatures increasing Al and Zn contents enhance dynamic recrystallization and dynamic precipitation, resulting in grain refinement and large amount of Mg17Al12 precipitates. As a result, the extruded Mg-9%Al-1%Zn alloy specimen shows high tensile strength of 370MPa, 0.2% tensile proof stress of 240MPa and moderate elongation of 20%, which are almost same as standard values of tensile properties of T5-treated 6N01 Al extruded alloy. Furthermore, a ratio of compressive proof stress to tensile proof stress of the as-extruded specimen improves up to a higher ratio of 0.9 than that of Mg-3%Al-1%Zn alloy specimen with no precipitation, 0.5, due to prevention of tensile twin, which easily occurs during compressive deformation even under a low applied stress perpendicular to the extrusion direction, by dynamic precipitation of Mg17Al12 phase.

Abstract: This paper reviews the latest research and development status of processing technologies for wrought magnesium alloys including extrusion, forging, (twin-roll) thin strip casting, rolling, stamping, and superplastic forming. Existing problems and the development trends of these processing technologies are analyzed and discussed. Up to the present, the R&D on the processing technologies of wrought magnesium alloys has made great global progress. Nevertheless there is a long way to achieve large-scale industrialization and application of wrought magnesium alloys.

Abstract: A recent trial investigated the effect of solidification grain refinement of billet on the grain refinement and properties of alloy ZM20. It was found that even at levels of 0.4Mn, significant grain refinement could be obtained when 0.7Zr was added. At 0.2Mn grain sizes as low as 60μm were obtained. Billets of Mg-2Zn-0.2Mn with four different grain sizes, due to different Zr and cooling rates were then cast via vertical direct chill casting and extruded conventionally. Benefits of grain refinement of the billet on extrusion were found to be a slight increase in the size of the operating window, and a reduction of the grain size in the extrudate. However, the effect of the reduction in extrudate grain size due to refinement of the billet was small compared with the amount of grain refinement obtained due to recrystallisation on extrusion.

Abstract: The thixoforming of wrought magnesium alloy was analyzed with computer numerical simulation based on rigid plastic/rigid viscoplastic finite element method. The simulated parameters were chosen and depended on the constitutive model of semi-solid AZ61 alloy that was established using the multiple nonlinear regression method in our prior literature. Thixo mechanical properties of semi-solid AZ61 alloy in high solid volume fraction were also analyzed. Behaviors of metal flow and temperature field were obtained, which were also compared with experimental data in literature. Research showed that the hard deformation magnesium alloy had great filling ability in semi-solid state, and the stress and strain distributions in workpiece after thixoforming were uniform. The semi-solid thixoforming technology has taken priority of the traditional processing.

Abstract: The structural changes of the wrought magnesium alloy AZ31B in semisolid state were clarified using optical microscopy and hot-stage microscopy. The influence of heat treatment variables was assessed. Compression tests covering a range from room temperature to 673 K were carried out for mechanical property assessment; flow stress and breaking strain were determined. The following are the results: (1) The grain growth of the hot-extruded AZ31B without preprocessing sensitively reacted at temperature and retention time. (2) The hot-extruded AZ31B with 30 % preprocessing showed an almost perfectly spheroidized structure in a semisolid state under certain conditions. (3) Heating velocity markedly affected the spheroidizing rate of grains. (4) From the direct observation of the hot-extruded alloy AZ31B by hot-stage microscopy, spheroidization was observed in some crystal populations. (5) Spheroided materials in the semisolid temperature range had a lower flow stress and a larger breaking strain than nonspheroidized materials. These results indicate the possibility of manufacturing wrought magnesium alloy by cold working.

Abstract: Comparing the formability with each other, extrusion and various rolling experiments were carried out to make fine-grained AZ31 Mg sheets, and uni-axial tensile tests were carried out at different strain rates and temperatures to investigate the effect of different variables. A warm deep drawing tool setup with heating elements, which were distributed under the die surface and inside the blank holder, was designed and manufactured, and deep drawing was performed. Extruded Mg alloy AZ31 sheets exhibit the best deep drawing ability when working in the temperature range 250-350°C. Extruded and rolled sheets of 0.8 mm thick were also deep drawn in the lower temperature range 105-170°C，showing good formability and reaching a Limit Drawing Ratio up to 2.6 at 170°C for rolled sheets. At last, a sheet cup 0.4 mm thick was deep drawn successfully at 170 °C.

Abstract: Recent research and development status of wrought magnesium alloys in China is reviewed, and more attentions are paid to structure controlling, plastic processing, welding, surface treatment and product application. The control of alloy phases, grain refinement, deforming behavior and twin-roll strip casting process are discussed. The existing problems on the research and development of wrought magnesium alloys in China are analyzed.

Abstract: Alloy phases in the as-aged (T6) ZK60 magnesium alloy were investigated. More attentions were paid to types and morphologies of main alloy phases in the as-aged ZK60 magnesium alloy. The experimental results indicated that there was an abundant flower-shaped segregation in the solution-treated ZK60 magnesium alloy. A small quantity of undissolved compounds, MgZn2, was also found. They distributed irregularly in the form of similar parallelogram, with a dimension of 200nm~500nm and not sensitive to heat-treatment. Mg2Zn3 was found to be a main secondary compound in the as-aged ZK60 alloy, which precipitated during aging. Another precipitation phase, MgZn, in the as-aged ZK60 magnesium alloy was also found in the form of long and thin rods with a dimension of 500nm.