Catarina Vidal

Optimization of FS Welding Parameters for Improving Mechanical Behavior of AA2024-T351 Joints Based on Taguchi Method

In the present study, the design of an experiment technique, the Taguchi method, has been used to optimize the friction stir welding (FSW) parameters for improving mechanical behavior of AA2024-T351 joints. The parameters considered were vertical downward forging force, tool travel speed, and probe length. An orthogonal array of L9 (34) was used; ANOVA analyses were carried out to identify the significant factors affecting tensile strength (Global Efficiency to Tensile Strength—GETS), bending strength (Global Efficiency to Bending—GEB), and hardness field. The percentage contribution of each parameter was also determined. As a result of the Taguchi analysis in this study, the probe length is the most significant parameter on GETS, and the tool travel speed is the most important parameter affecting both the GEB and the hardness field. An algebraic model for predicting the best mechanical performance, namely fatigue resistance, was developed and the optimal FSW combination was determined using this model. The results obtained were validated by conducting confirmation tests, the results of which verify the adequacy and effectiveness of this approach.

Mechanical Characterization of Friction Stir Channels under Internal Pressure and In-Plane Bending

Friction Stir Channelling (FSC) is a simple and innovative technique of manufacturing integral and continuous channels (also referred as conformal channels) in monolithic plates in a single step. This paper is focused on the mechanical behaviour of integral and continuous FS channels produced in a monolithic plate of the aluminium alloy AA7178‑T6 with 13mm of thickness, typically used in structural aircraft applications. Internal pressure tests were conducted on specimens with a longitudinal friction stir channel. In-plane bending tests were carried out in specimens with longitudinal and transversal channels; different conditions were analysed for each FSC parameters set. Results were analysed and compared concerning the FS channels microstructure and base material mechanical properties. Bending tests results show that tool rotation speed has more influence in the FSC specimens bending strength than tool travel speed and internal pressure tests show that increase tool rotation speed increases the minimum pressure that leaking points arise.

Role of Friction Stir Channel Geometry on the Fatigue Behaviour of AA5083-H111 at 120°C and 200°C

Friction StirChannelling (FSC) is an innovative solid-state manufacturing technology able toproduce, in a single step, continuous integral channels in monolithic platesthat can be used to produce conformal cooling systems as well as heatexchanging devices. FSC is based on the same principles of Friction StirWelding (FSW) process and the features of the channels produced by FSC can becontrolled by the processing parameters and tool geometry. Bending fatiguetests have been performed using friction stir channelling specimens of 5083‑H111aluminium alloy with different channel geometries. Fatigue tests have beencarried out at 120°C and 200°C in a servo-hydraulic testing machine coupledwith a furnace, in order to understand the role of channel geometry on thefatigue behaviour at elevated temperature. Results were compared with thoseobtained at room temperature. The specimens were tested until fracture or up to 3x106 cycles. For the channel geometries tested, the fatiguestrength of friction stir channelling specimens is dependent on the testingtemperature, decreasing with the temperature increased. At all temperaturesstudied, for both channel geometries, fatigue-crack always initiated into theinterior of the specimen, namely on the boundary between the channel nugget andthe thermo‑mechanically affected zone. It was observed that crack initiationhas been occurred earlier at elevated temperature than at room temperature.

Modelling Microstructural Effects on the Mechanical Behaviour of a Friction Stirred Channel Aluminium Alloy

Friction stir channelling (FSC) is a relatively new solid-state manufacturing technology able to produce conformal channels in a monolithic plate in a single step. During the FSC process the metal workpiece material is softened by the heat energy generated from dissipation during: plastic deformation, internal material flow and frictional work between the tool and the metal workpiece. The mechanical performance of a friction stirred channel aluminium alloy is affected by microstructure surrounding the channel. A new methodology that simulates a realistic 2D microstructure from experimental metallographic characterization and tensile tests was developed using the commercial software ABAQUS to study the mechanical behaviour of the friction stirred channel 5083-H111 aluminium alloy. Fourpoint bending tests were simulated and compared with experimental results. The RambergOsgood model was also adopted in the finite element analysis. It is seen from this investigation that microstructure can significantly affect the bending strength of friction stirred channel plates.