Effect of welding parameters on mechanical and microstructural properties of AA6082 jointsproduced by friction stir welding

The effect of processing parameters on mechanical and microstructural properties of AA6082 joints produced by friction stir welding was analysed in the present study. Different welded specimens were produced by employing a fixed rotating speeds of 1600rpm and by varying welding speeds from 40 to 460 mm/min. The joints mechanical properties were evaluated by means of tensile tests at room temperature. In addition, fatigue tests were performed by using a resonant electro-mechanical testing machine under constant amplitude control up to 250 Hz sinusoidal loading. The fatigue tests were conducted in axial control mode with R = min/max = 0.1, for all the welding and rotating speeds used in the present study. The microstructural evolution of the material was analysed according to the welding parameters by optical observations of the jointed cross-sections and SEM observations of the fractured surfaces were done to characterize the weld performances

Effect of welding parameters on mechanical and microstructural properties of dissimilar AA6082–AA2024 joints produced by friction stir welding

The effect of processing parameters on the mechanical and microstructural properties of dissimilar AA6082-AA2024 joints produced by friction stir welding was analysed in this study. Different samples were produced by varying the advancing speeds of the tool as 80 and 115 mm/min and by varying the alloy positioned on the advancing side of the tool. In all the experiments the rotating speed is fixed at 1600 RPM. All the welds were produced perpendicularly to the rolling direction for both the alloys. Microhardness (HV) and tensile tests performed at room temperature were used to evaluate the mechanical properties of the joints. The mechanical tests were performed on the joints previously subjected to annealing at 250 °C for 1 h. For the fatigue tests, a resonant electromechanical testing machine was employed under constant loading control up to 250 Hz sine wave loading. The fatigue tests were conducted in the axial total stress-amplitude control mode, with R = σmin/σmax = 0.1. In order to analyse the microstructural evolution of the material, the welds' cross-sections were observed optically and SEM observations were made of the fracture surfaces

Thermoelasticity and CCD analysis of crack propagation in AA6082 friction stir w elded joints

The advantages of friction stir welding (FSW) process compared to conventional fusion welding technologies have been clearly demonstrated in recent years. In the present study, AA6082 FSW joints were produced by employing different welding parameters. The principal aim of this work is to apply thermoelastic stress analysis (TSA) to study crack propagation characteristics of friction stir welded aluminum sheets, during cyclic fatigue tests. The crack propagation experiments were performed by employing single edge notched specimens; fatigue tests were performed under tension with load ratio R = 0.1. All the mechanical tests were conducted up to failure. The TSA measurement system allowed crack evolution to be observed in real-time during fatigue cycles and stress fields to be derived on the specimens from the measured temperature variation. The thermoelastic data were used to analyse principal stresses and principal strains on the specimens surface and the crack growth rate during tests. In addition, it was possible to evaluate all the joints defects effects, as a function of welding parameters, correlating effects on different crack growth rate and instabilities. The achieved results were compared with those obtained by classical CCD camera monitoring of crack front propagation during cyclic loading and all the results were validated by employing finite element analysis performed with ABAQUS software

Mechanical and microstructural behaviour of 2024–7075 aluminium alloy sheets joined by friction stir welding

The aim of the present work is to investigate on the mechanical and microstructural properties of dissimilar 2024 and 7075 aluminium sheets joined by friction stir welding (FSW). The two sheets, aligned with perpendicular rolling directions, have been successfully welded; successively, the welded sheets have been tested under tension at room temperature in order to analyse the mechanical response with respect to the parent materials. The fatigue endurance (S–N) curves of the welded joints have been achieved, since the fatigue behaviour of light welded sheets is the best performance indicator for a large part of industrial applications; a resonant electro-mechanical testing machine load and a constant load ratio RZsmin/smaxZ0.1 have been used at a load frequency of about 75 Hz. The resulted microstructure due to the FSW process has been studied by employing optical and scanning electron microscopy either on ‘as welded’ specimens and on tested specimen after rupture occurred

Laser Marking of Titanium Coating for Aerospace Applications

Abstract In the aerospace industry, in order to ensure the identification and the traceability of the products, high repeatability, non-invasive and durable marking processes are required. Laser marking is one of the most advanced marking technologies. Compared to traditional marking processes, like punches, microdot, scribing or electric discharge pencil etcher, laser marking offers several advantages, such us: non-contact working, high repeatability, high scanning speed, mark width comparable to the laser spot dimension, high flexibility and high automation of the process itself. In order to assure the mark visibility for the component lifetime, an appropriate depth of the mark is required. In this way, a stable behaviour is ensured also when the component operates in aggressive environments (i.e. in presence of oxidation, corrosion and wear phenomena). The mark depth is strongly affected by the laser source kind and by the process parameters, such us average power, pulse frequency and scanning speed. Moreover, an excessive mark penetration could cause stress concentrations and reduce the fatigue life of the component. Consequently, an appropriate selection of the process parameters is required in order to assure visibility and to avoid excessive damage. Cold Spray Deposition (CSD) is a relative new technology that allows to produce surface coatings without significant substrate temperature increasing. In aeronautics fields this technology is useful to coat materials sensible to temperature, such as solution tempered aluminum alloy, with a titanium layer. Aim of the work is to characterize the laser marking process on CSD Ti coating, in order to study the influence of the laser marking process parameters (pulse power and scanning speed), on the groove geometry of the marking. The experimental marking tests were carried out through a 30 W MOPA Q-Switched Yb:YAG fibre laser; under different process conditions. The groove geometry was measured through a HIROX HK9700 optical microscope. The results showed the effectiveness of the laser process to produce high quality marks on the titanium layer. Moreover, a correlation between the process parameters and the mark's geometry was clearly observed

High-efficiency mixing of fine powders via sound assisted fluidized bed for metal foam production by an innovative cold gas dynamic spray deposition method

Metal foams are an interesting class of materials with very low specific weight and unusual physical, mechanical and acoustic properties due to the porous structure (1). These materials are currently manufactured by means of several conventional processes (2), limited by the impossibility to produce foams with complex geometry. This paper deals with the study of an innovative method to produce complex shaped precursors for aluminum foams through cold gas dynamic spray deposition process (CGDS), aluminum alloy (AlSi12) and titanium-hydride (TiH2) being the metal and the blowing agent, respectively. However, the success of this approach strongly depends on the achievement of a homogenous and deep mixing between AlSi12 and TiH2 fine powders, belonging to group C of Geldart’s classification. Classical mixing methods (such as tumbling mixers, convective mixers, high-shear mixers, etc.) are suitable for large non-cohesive particles (\u3e 30µm) but not for micronic particles (3), agglomerated due to strong interparticle forces. Alternatively, new wet and dry mixing techniques have been proposed for fine particles (4), suffering from different disadvantages: additional steps of filtration/drying are needed for wet methods, whereas, dry methods generally involves the reduction of the granulometry and the damaging or contamination of the original powders. The sound assisted fluidization technology (140dB-80Hz) has been adopted in this work to overcome the technical issues of mixing cohesive powders (5), thus obtaining a mixing to the scale of the primary particles in a simple, economic, not intrusive and not destructive way (the properties and morphology of the original particles were preserved). Therefore, the mixed powders were then sprayed by means of the proposed CGDS process on a stainless steel sheet to obtain the precursor. This was then heated up in a furnace at 600°C for 10 minutes to obtain the foam. In particular, two different types of mixtures with 1 wt% and 2.5 wt% of TiH2 were investigated; moreover, air compressed as well as helium were used as CGDS carrier gas in order to ensure a higher impact velocity and a better compacting of the powders. A very efficient mixing of powders has been achieved as confirmed by SEM/EDS analysis performed on samples taken from the sound assisted fluidized bed (Fig.1a) and by the time-dependence of the mixing degree (Fig.1b). Macrographs of created porous structures (Fig.2) showed that the coupling of sound assisted fluidization and CGDS process under optimal conditions is a promising and effective technique in manufacturing aluminum precursors for metal foams. Please click Additional Files below to see the full abstract

Saldatura in configurazione testa a testa di lamiere in lega 2198 T3 mediante procedimento friction stir welding

Scopo del presente lavoro è lo studio della saldabilità mediante processo friction stir welding (FSW) di lamierein lega innovativa alluminio-litio AA 2198 T3 in configurazione di testa. In particolare, mediante tecnichestatistiche, la velocità d’avanzamento e quella di rotazione sono state messe in relazione con le proprietàmeccaniche del giunto ed è stato sviluppato un modello empirico di previsione delle suddette caratteristiche alvariare dei parametri di processo. Per lo sviluppo di questo modello, è stato utilizzato un piano fattorialecompleto 32 avente come risposte osservate la resistenza allo snervamento e la resistenza a rottura dei giunti.Il modello sviluppato può essere utilizzato per prevedere le proprietà meccaniche dei giunti con un livello diconfidenza pari al 95%. Inoltre, usando la funzione di desiderabilità (desirability function, DF) sono statitrovati i parametri di processo che massimizzano in maniera bilanciata la resistenza allo snervamento equella alla trazione. Infine, i giunti ottenuti utilizzando i parametri di processo ottimi sono stati sottoposti aprove di fatica e di tensocorrosione al fine di valutarne il potenziale utilizzo nel settore aeronautico. I risultatiottenuti mostrano che i giunti ottenuti tramite questa tecnologia hanno una buona resistenza allatensocorrosione ed un’ottima vita a fatica, paragonabile a quella del materiale base e superiore a quella disaldature ottenute con tecniche tradizionali, come TIG e MIG