Search

The friction stir welding process was simulated for joining AA6082 aluminum alloy with the use of the computational fluid dynamics method. Two different tool geometries were used—a tapered cylindrical pin (simple pin) and a hexagonal pin with grooves (complex pin). The analysis of the simulations performed was discussed in terms of temperature evolution during the process, total heat input, residual stresses and material flow. Simulations revealed that a 5% higher temperature, equal to maximum 406 °C, was provided when using the complex pin than with the simple pin. Higher temperature and higher shear stresses during the welding with the complex pin caused the introduction of higher residual stresses in the weld. Experimental results on the produced welds allowed observation of the microstructure of the joints, hardness tests in cross sections and tensile strength tests. Due to the higher temperature during the process with the complex pin and the more efficient recrystallization process, grain refinement in the SZ was more pronounced. The average grain size in the stir zone for the weld produced with the complex pin was equal to 11 ± 1 µm, and in the case of the simple pin 14 ± 1 µm. The presented hardness profiles revealed that the weld produced with a complex pin had higher hardness in the stir zone, equal to 89.5 ± 1.3 HV, which is consistent with the Hall-Petch relationship. The obtained UTS values corresponded to the joint efficiency of 72.5 ± 4.9% and 55.8 ± 8.6% for the weld produced with the complex pin and the simple pin. [ABSTRACT FROM AUTHOR]

The Friction Stir Welding (FSW) method was employed to join AA6082 sheets. The welds were produced with different tool traverse speed (200 and 250 mm/min), rotational speed (1000 and 1250 RPM) and tool tilt angle (0 and 2 deg). Based on the analysis of XRD patterns, the total precipitation volume fractions in the nugget zones and the base material were calculated. The FSW process resulted in a reduction in the fraction of precipitates up to 64 pct compared to the parent material. Based on the Williamson–Hall analysis and indentation tests, the residual stresses were calculated. The highest tensile residual stresses of − 89.09 ± 6.19 MPa were observed for the base material, and the welding process reduced the residual stresses. The calculated dislocation density in the parent material AA6082 was equal to 8.225 × 1013 m−2, while in the welds a decrease was observed up to the value of 1.419 × 1013 m−2. In addition, the FSW process changed the nature of dislocations with edge-type dislocations dominating, while screw dominating character of dislocations were prevalent in the parent material. The mobility of dislocations in the studied welds was higher and reached the value of 16.78 × 10–7 m s , while the dislocation mobility in the parent material was equal to 3.19 × 10–7 m s . Process parameters during welding have a crucial effect on the amount of heat and strains introduced during the process, and thus influence the residual stresses, dislocation density and mobility, which might have a fundamental impact on the properties of the produced welds. [ABSTRACT FROM AUTHOR]

The thermo-mechanical behavior of nanosized Al2O3 particles reinforcing aluminum was analyzed in the present paper. The material was prepared by spark plasma sintering and friction stir welding. The thermal stresses affecting the composite behavior during welding were modeled through COMSOL MultiPhysics, and the results were validated by the analyses of the composites' mechanical properties. The spark-plasma-sintered materials presented limited porosity, which was taken into account during the modeling phase. Both model and experiments revealed that higher heat input is related to better material mixing during welding and sound mechanical properties. Thermal stresses lead to residual stresses close to 300 MPa in the thermo-mechanically affected zone for processing conditions of 1900 RPM and 37 mm/min. This leads to an increase in hardness up to 72 HV. [ABSTRACT FROM AUTHOR]

Cold-spray coatings were produced by FeCoCrNiMn high-entropy alloy powders deposited on carbon steel substrate. The coatings were realized at intermediate temperature and high pressure (at 1100 °C and 7 MPa). The coating microstructure was characterized by scanning electron microscopy and X-ray diffraction, revealing a very dense deposition and high flattening ratio of the splatted particles. This had a large influence on the strong adhesion of the coating to the substrate. The hardness and residual stress profiles were measured through nanoindentation and X-ray diffraction from the peak broadening measured layer by layer. The cyclic behavior of the coatings was evaluated through three-point bending tests performed on V-notched samples coated via cold spray. Cyclic tests were performed at different maximum strokes from 0.3 to 3.6 mm in order to monitor the crack initiation and propagation during bending tests. The fracture surface aspect was analyzed by scanning electron microscopy in order to reveal the fracture mechanisms in different deformation conditions. [ABSTRACT FROM AUTHOR]