Papers by Keyword: Mg-Al Alloys

Abstract: Magnesium and magnesium alloys offer high potential as lightweight materials. Current works are mainly focused on the metal forming technologies and material development for sheet and strips to provide magnesium flat products for industrial applications. However, the technology for the production of magnesium long products for fasteners or other connecting elements is exclusive the extrusion process. A cost-efficient alternative can be the caliber rolling technology for magnesium rods and wire with regard to refined microstructure and specific required properties. But this whole process is rarely applied up to now and all material-specific as well as deformation relevant basics must be developed and additionally validated under industrial conditions. This paper gives the overview for a magnesium-specific wire rolling technology under consideration of chemical composition (AZ31, AZ61, AZ80) and their influence to final mechanical properties in correlation with the microstructure evolution along the whole process line. Therefore, the process-and material-dependent microstructural evolution during rolling process was investigated. The structural constitution is detailed by the grain size and the precipitation conditions. For the determination of the mechanical properties hardness measurement as well as tensile testing was carried out. To preliminary design and determine the material flow, the temperature distribution, and the logarithmic strain, a commercial numerical simulation tool was applied on base of the implemented material-specific deformation and recrystallization behavior. Hence, it was possible to design a magnesium specific caliber sequence for the production of fine-grained magnesium wires with Ø 8 mm and excellent mechanical properties.

Abstract: The Mg-Al alloys are the best-known and most commonly used magnesium alloys (especially AZ91 alloy). However, the AZ91 alloy offers insufficient corrosion resistance. Many investigations show that hydrogen is the main corrosive factor appearing during chemical reactions between magnesium and water in electrolyte solution. The main intermetallic phase in the AZ91alloy is the Mg₁₇Al₁₂ (β phase), which is a hydrogen trap. During corrosion, magnesium hydride forms inside the β phase, and this phase is brittle fractured when the inner stress caused by hydrogen pressure and expansion stress due to the formation of magnesium hydride is higher thanthe fracture strength. We examined the corrosion behaviour of AZ91 and AE44 magnesium alloysin 0.1M Na₂SO₄ solution and 3.5% NaCl solution. We analysed two Mg-Al alloys in order todetermine the various effects of hydrogen on these materials.

Abstract: A systematic investigation was carried out in the present study to study the impact of solidification variables like thermal gradient (G), solidification velocity (V) and cooling rate on the second phase fraction and microsegregration in Mg-Al (3, 6 , 9 wt.%) binary alloys. Solidification experiments such as directional solidification and gravity castings were conducted to obtain a cooling rate in the range of 0.05-700 K/s. The experimental results were tested against the microstructural modeling data and a reasonable agreement was obtained between them.

Abstract: Recrystallization kinetics of Mg alloy has been investigated in this study. Mg alloys such as Mg-3Al and Mg-6Al in weight percents were cast into rectangular shaped ingots of 20mm thickness. Solution treatment at 400°C for 24 hrs has been carried out on these ingots and pure Mg for comparison. Heat treated ingots including pure Mg were rolled at room temperature by thickness reductions of 10, 20, and 30 percents. Annealing treatment for recrystallization has been conducted on these cold-rolled plates at temperatures of 200, 300, and 400°C for various times from 1 min to 24 hrs. The microstructure observation and hardness measurement conducted on the recrystallized specimens revealed that static recrystallization at 200°C was very slow and expedited with increasing temperature, regardless of Al contents. While recrystallization behavior of Mg at 300°C appeared to be retarded by increase in Al contents, that of Mg was not affected at 400°C.

Abstract: We studied the effects of solution RPM, bath temperature, and time in anodizing AZ91 under a constant current density of 750 mA/cm2 in a 1 M NaOH solution. In general, increasing the anodizing time, RPM, and temperature of the bath improved the corrosion resistance. The thickness of the anodic oxide film likely grew by increasing the time required to generate the active dissolution reaction. When anodizing at 750 mA/cm2, we evaluated a 300–3600-s range in anodizing time, 0–1500 RPM, and 296–373 K bath temperatures, and determined that 3600 s, 1500 RPM, and 373 K comprised the optimum conditions.

Abstract: Heterodiffusion of 65Zn in Mg, Mg – x Al (x = 1.77, 3.9 and 9 wt.% Al) and in the commercial AZ91 alloy was studied in the temperature interval 498 – 848 K by serial sectioning and residual activity methods. The concentration and temperature dependence of Zn bulk diffusion coefficient D is described by the relation D = exp (0.1 × cAl – 9.16) × exp (-125.8 kJ mol-1/RT) m2 s-1 (cAl – concentration of Al in wt.%). Zn grain boundary diffusivity P = s δ Db (s – segregation factor, δ - grain boundary width and Db – diffusion coefficient in grain boundary) was also determined and it was found that it obeys the Arrhenius law P = 7.2 × 10-15 × exp (-46 kJ mol-1/RT) m3 s-1.

Abstract: A small amount of Zn or Sn was added to Mg-3%Al alloy to improve the formability of alloy. The elongation of as-rolled alloy was increased at both room temperature and 300oC by addition of Sn or Zn, even though the tensile strength at room temperature was remarkably increased only by Zn. When the as-rolled alloy was annealed to be fully recrystallized, the ductility at room temperature was significantly enhanced, however the elongation at 300oC was rather decreased probably attributed to the dynamic recrystallization occurred during the tensile test.

Abstract: This paper investigated the effects of anodizing time on the formation of anodic oxide films on a Mg-Al alloy in alkaline solution. The thickness of the anodic oxide film was increased by increasing the time required to generate the active dissolution reaction. When anodizing at various anodizing time, the potential after passivity increased with time, which implies growth in film thickness. When the anodizing time was varied, the quantity of oxygen increased with time in the white areas (the film), i.e., more film was observed in the SEM and EDX analyses.

Abstract: The fundamentals of grain refinement are reviewed with particular focus on magnesium alloys. This is followed by considerations of the theoretical and practical aspects of grain refinement of Mg-Al alloys by carbon-based grain refiners. Finally, experimental results using Al4C3 as a potential grain refiner are presented and discussed.

Abstract: The effects of sealing solutions on the corrosion resistance of anodized Mg-Al alloys were investigated. As the proportion of Mg(OH)2 increases with the increase in the NaOH concentration, the corrosion potential improves. The sealing effects were further improved by increasing the temperature of distilled water, the pH of solutions, and the proportion of Mg(OH)2 present in the anodic film.