چكيده به لاتين
Non-heat-treatable 5xxx series aluminum alloys have been widely used in marine industries, coastal structures, fuel tanks, and chemicals transportation, aerospace, and also military industries due to their combination of mechanical and chemical properties. These alloys acquire their tensile strength through the solubility of magnesium atoms as a substitution solid solution in the aluminum, but during heat treatment, these atoms leave from solid solution and precipitate as β (Al3Mg2) phase at the grain boundaries which reduce the strength and cause the alloy highly susceptible to intergranular corrosion. Combination of cold rolling and stabilizing annealing is the common temper used in these alloys (H321). This temper enhances the strength and provides the best properties for corrosion resistance. The optimal thermo-mechanical treatment is difficult to be found due to two problems that exist in these alloys called age softening and Portevin - Le Chatelier phenomena. In this study, the optimal thermo-mechanical cycle has been determined for producing 1 mm thick AlMg6 sheets. The effect of deformation and annealing temperature on the microstructure, hardness, and tensile strength of the alloy were also investigated. For this purpose, optical microscopy (OM), scanning electron microscopy (SEM), field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), Brinell hardness measurement (HB), micro Vickers hardness (mHV) and tensile test were used in this research. A method including mass reduction in Nitric Acid (NAMLT) solution was used in order to determine the optimum conditions for stabilization and calculation of corrosion resistance. The temperature and time of the complete annealing of the samples were determined. Its mechanical properties were compared with the stabilized samples and also with the standard annealed samples. In this research, a structure with micrometric precipitates of 4μm, nano-scale precipitates of 30 nm, and grains with a mean diameter of 15μm were obtained. The yield stress and tensile strength of the stabilized sample increased 23 and 20%, respectively and reached to 343MPa and 420MPa, respectively. Its elongation increased about 44% from the original sample and reached 13%. The yield strength, tensile strength, and elongation in annealed conditions increased by 65, 30, and 33%, respectively; and reached to a 160MPa, 310Mpa, and 21%, respectively.
Keywords: Cold Roll, Anneal, Thermomechanical Process, NAMLT Corrosion, AlMg6
