چكيده به لاتين
The rolling process is used as one of the methods of production and deformation on aluminum alloy sheets. In order to achieve the optimum properties of strength and formability of aluminum sheets, in addition to cold work, it is necessary to perform heat treatment on these sheets. Since microstructure is an important factor in determining the properties of this alloy, in this study, the effect of heat treatment on the microstructure, tensile properties and plastic deformation of an AlMg6 alloy sheet has been investigated in order to achieve optimum conditions. In this research, the sheet was first subjected to heat treatment, uniaxial tensile test and hardness measurement in order to use the results of tensile test to calculate the work hardening and anisotropy parameters. Optical Microscopy (OM), Scanning Electron Microscopy(SEM), X-Ray Diffraction(XRD) and Energy Dispersive Spectroscopy(EDS) were used to study the microstructure. The average grain size was calculated using OM and SEM results and the existing phases in the field were identified and analyzed using EDS and XRD. Dislocation densities are calculated based on Williamson-Hall theory using X-ray diffraction results peaks. By comparing the results of tensile and microstructure tests, the optimum heat treatment conditions were 415°C and 15 min. The values of yield stress, ultimate tensile strength and percentage of plastic uniform elongation under optimum conditions were 166.5MPa, 354MPa and 15.2% in the rolling direction, respectively. The amount of hardness in the As recieved sample was 106HV, which was reduced to 80 HV5 in the Optimum sample. The amount of strain-hardening exponent has also increased from 0.139 to 0.276 in the optimum sample. The anisotropy parameter values in the As recieved sample were 0.57 which changed to 0.54, which indicates that little change in anisotropy occurred. In the As recieved sample and the optimum sample, the mean of the grain sizes were 44.1μm and 35.6μm, respectively, and the density of dislocations was 10.2×109(cm-2) and 8.58×109(cm-2) respectively. The results of this research showed that the applied heat treatment have reduced the density of dislocations, increased the hardness, reduced the grain size and increased the percentage of plastic uniform elongation, as factors to increase the formability. Also, microstructural studies showed that the distribution of secondary phases, especially phase, plays a key role in the strength of the alloy. Examination of fracture levels of uniaxial tension tested specimens showed that the fracture in the optimum specimen occurred ductile or soft, while in the optimum sample the fracture mechanism was semi-soft.
