RESUMEN
The aim of this research was the selection of friction stir welding (FSW) parameters for joining stiffening elements (Z-stringers) to a thin-walled structure (skin) made of 1 mm-thick EN AW-2024 T3 aluminium alloy sheets. Overlapping sheets were friction stir welded with variable values of welding speed, pin length (plunge depth), and tool rotational speed. The experimental research was carried out based on a three-factor three-level full factorial Design of Experiments plan (DoE). The load capacity of the welded joints was determined in uniaxial tensile/pure shear tests. Based on the results of the load capacity of the joint and the dispersion of this parameter, multi-criteria optimisation was carried out to indicate the appropriate parameters of the linear FSW process. The optimal parameters of the FSW process were determined based on a regression equation assessed by the Fisher-Senecor test. The vast majority of articles reviewed concern the optimisation of welding parameters for only one selected output parameter (most often joint strength). The aim of multi-criteria optimisation was to determine the most favourable combination of parameters in terms of both the smallest dispersion and highest load capacity of the joints. It was found that an increase in welding speed at a given value of pin length caused a decrease in the load capacity of the joint, as well as a significant increase in the dispersion of the results. The use of the parameters obtained as a result of multi-criteria optimisation will allow a minimum load capacity of the joints of 5.38 kN to be obtained with much greater stability of the results.
RESUMEN
In this study, the influence of sandblasting process parameters as a surface preparation method on the strength of single-lap adhesive joints of EN AW 2024 T3 aerospace aluminium alloy sheets was determined. Eleven sets of sandblasting parameters were used, which were determined according to a determined experimental plan. The variable factors in the sandblasting process were pressure, nozzle distance, and workpiece displacement speed. The sand jet incidence angle was constant. Garnet 80 E+ was the abrasive material that was used. The joints were made using an epoxy adhesive composition of Epidian 5 epoxy resin and a PAC curing agent. The influence of the surface preparation method on the surface roughness and contact angle to determine the surface free energy was evaluated. The shear strength of the adhesive joints was also determined, which finally allowed the evaluation of the applied surface treatment variants. The obtained results were subjected to statistical analysis, which indicated that the highest shear strength of the adhesive joints was obtained for samples whose surfaces were treated by sandblasting at parameter configurations in which the pressure was 5-6 × 105 Pa; the distance between the nozzle and the sandblasted surface should not be greater than 97 mm, and the speed at which the workpiece moves in relation to the nozzle should not be greater than 75 mm/min.
RESUMEN
This work concerns mechanical properties in relation to microstructural changes in hardenable EN AW-2024 aluminium alloy in wrought and heat treated condition. The treated material benefits from synergistic effects of hardening mechanisms. Grain boundary strengthening and work hardening were activated in this material by rotary swaging. Rotary swaging is a method which shows great promise for industrial use. Precipitation hardening was achieved thanks to the material's age hardening ability. First, the material was artificially-aged in a furnace at 140-180 °C. Second, natural ageing was used. Mechanical properties of the as-treated material were tested and microstructural processes were explored using electron microscopy and differential scanning calorimetry. The treatment route which delivered the best results was as follows: solution annealing 500 °C/1 h + water cooling + rotary swaging + artificial ageing 160 °C/21 h. This led to a yield strength close to 640 MPa, and ultimate strength above 660 MPa, and elongation of 8%. Electron backscatter diffraction observation revealed that in this condition, the ratio of Low-angle to High-angle grain boundaries is 80:20. The microstructure contains both T-phase in the interior of grains, whose particles are normally oval-shaped, and S-phase, which is present in two shapes: small oval particles or coherent needles aligned to <100> direction.