Papers by Keyword: AZ61

Abstract: The current paper focuses on enhancing the manufacturability of AZ61 magnesium alloys by heat treatment. Specimens are subjected to solution heat treatment. First, all samples underwent a 15-hour treatment at 415°C before aging at 50°C, 100oC, and 150°C. The specimens were furnace cooled and quenched after achieving the precise aging temperature. The results have been extracted from tensile and cupping tests. The outcomes of each test have been compared with the data taken without heat treatment, so the ductility increase can be observed. Tests revealed better results for furnace-cooled specimens. The increase in formability of about 9% along with a decrease in strength of only 11% is observed for 150°C aging temperature.

Abstract: We chose cast and extrude magnesium alloy AZ61 as materials and studied the influences of temperature, humidity, pressure and NaCl atmosphere on the corrosion products and corrosion mechanism by means of SEM, EDS and XRD. we could indicate the corr osion rate of extruded AZ61 magnesium is faster than that of cast AZ61 magnesium. Both th e rearrange of second ph ase and smaller grain size, which owing to the extrusion process, change the morphologies of corrosion products.

Abstract: The effects of Y and Gd on the microstructure and mechanical properties of AZ81 magnesium alloy were studied by alloy preparation, microstructure analysis and mechanical property testing. The results show that moderate addition of Y and Gd to AZ61 magnesium alloy can obviously refine grains of AZ61 alloy, and decrease the amount of Mg₁₇Al₁₂ phase. With the increase of alloying elements, the tensile strength and elongation of aged AZ61 magnesium alloy at the temperature ranging of 25°C～175°C rise at first and then drop.When content of Y and Gd is up to 2.7%，the values of tensile strength of the alloy at room temperature and 175°C are up to their maximums, 254MPa and 164MPa respectively, while the elongation of the alloy are 22.9%,18.7% respectively. Y and Gd improve the mechanical properties of AZ61 alloy because of the grain refining strengthening, solution strengthening and the dispersion strengthening.

Abstract: Grain refinements during hot compression of continuous casting AZ80 alloy bars and extrusive AZ61, AZ80 alloy bars were observed. The hot compression true stress-true strain curves of extrusive AZ61 and AZ80 alloy had similar tendencies, which were that the true stress increased and had a peak around 0.2 true strain, and then the stress decreased and was almost even from about 0.4 true strain. The stress peaks shifted to the high strain side as the compression speed, true strain speed, increased. However, the stress peaks did not shift at different compression temperatures. Fine grains were obtained under the condition of high strain speed and low temperature, but the grain sizes were uneven at low temperature compression. The stress peaks in the hot compression true stress-true strain curves of continuous casting AZ80 did not shift at different compression temperatures. AZ80 forging products with fine grains are expected to be formed under various conditions by using continuous casting AZ80.

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 effect of Ca, Sc and Er microalloying on the microstructure and properties of AZ61 alloys by electromagnetic casting are investigated. Experimental results show that an addition of Ca, Sc and Er refine the grains and compounds of AZ61 alloy. Mg17-xCaxAl12 phase are obtained after Ca addition. When the Ca, Sc and Er added in AZ61 alloy, some new phase contain Ca, Sc and Er are appeared. The tensile properties are improved as a result of grains and compounds refinement arter Ca, Sc and Er microalloying.

Abstract: In this paper, the solution mainly containing Zn(H2PO4)2 was used to prepare phosphating coatings on AZ31,AZ61 and AZ91 magnesium alloys. The effects of the phosphating parameters and the composition of phosphating solution on the formation of the coatings were investigated by orthogonal tests. The corrosion behaviors of the phosphating coatings were also studied and it is found that there was no hydrogen evolution in at least 1h. In the last, 60~80μm organic coatings were painted on the phosphated magnesium alloys,the organic coatings adhered to the phosphating coating, and the anti-corrosion abilities were improved .

Abstract: The fatigue crack propagation (FCP) behavior of magnesium alloy AZ61 at room temperature (RT), elevated temperature (60°C, 120°C) , and in ambient and wet air was investimated. The mechanisms of FCP were discussed in detail. It was demonstrated that The FCP rate of AZ61 magnesium alloy increased with increasing temperature and relative humidity (RH). Obvious change in the microstructure occurred during fatigue at elevated temperature, particularly at 120°C, compared to its original microstructure. Grain growth, deformation twin, grain boundary (GB) immigration and precipitates were observed in the microstructure at 120°C after fatigue. A bend occurred in the curves of FCP rate versus stress intensity factor at 120°C, which corresponded to a transition of failure mode from a mixed intergranular and transgranular fracture to a transgranular fracture. At first stage, the FCP rate increased sharply, and then went up slowly due to the growth of grain size. Secondary phase particles facilitated the fatigue crack initiation. The Hydrogen embrittlement (HE) may be primarily responsible for accelerating FCP rate in wet air.

Abstract: The effect of second phase on the mechanical properties of AZ61 and AZ91 Mg-Al-Zn magnesium alloy processed by equal-channel angular extrusion (ECAE) has been investigated. The results revealed that cracks initiated at and propagated through the α-Mg/β-Mg17Al12 interfaces and grain boundaries of Mg-Al-Zn alloys during tensile deformation. For AZ61, the elongation increased with the increase of ECAE pass number and the decrease of grain size. However, the elongation of AZ91 with more second phase particles decreased with the increase of ECAE pass number and the decrease of grain size.

Abstract: In this study, AZ31 in form of sheet, plate and extruded rod and AZ61 wire with different initial grain sizes were used to investigate the effect of initial grain size on recrystallization behavior and the formation of fine recrystallized grain (the so-called necklace) structure. Nucleation and growth of recrystallized grains along grain boundaries has been examined. In order to observe the effect of initial grain size and deformation on static recrsytallization and necklace formation, the specimens were annealed at 100-250°C for 10min--2hr. Specimens are also stretched to a total strain of 10, 20 and 40% at 300°C at an initial cross head speed of 1x10-3 s-1 for dynamic recrystallization studies. The results suggest that there exists a grain size limit, below which a necklace structure is not observed.