Studio di saldabilità (LBW,FSW, EBW) di leghe da pressocolata a base alluminio

Le leghe da pressocolata sono generalmente difficilmente saldabili con i processi ad arco tradizionali acausa dei cicli termici di saldatura blandi che possono provocare la precipitazione di fasi fragili in ZTA e altempo stesso la complicata geometria dei pezzi può di fatto rendere inapplicabili certe tecnologie(saldature in interstizi non raggiungibili con torce di saldatura tradizionali). Di qui l’esigenza di uno studiodi saldabilità con processi alternativi come quelli ad energia concentrata (fascio laser e fascio elettronico) oil caratteristico processo Friction Stir che permette di saldare facilmente materiali basso fondenti come leleghe di alluminio senza portarle a fusione (fattore che in questo caso può rivelarsi molto positivo). Lo studio inquestione ha previsto l’utilizzo delle tre tecnologie di saldatura sopracitate tramite la tecnica conosciuta come“beads on plate” che consiste nella realizzazione di cordoni di saldatura direttamente su materiale base senzaunire fisicamente due pezzi ma che di fatto permette ugualmente di stabilire l’applicabilità o meno di undeterminato processo. Come materiali per la sperimentazione è stato previsto l’utilizzo di lastrinepressofuse da 2 e 4 mm di spessore, di due differenti leghe Al/Si modificate allo Stronzio riconducibili ai gruppiAlSi9Mn ed AlSi9MgMn. La prima caratterizzata dall’assenza di Magnesio, la seconda con tenori dello stessocompresi fra lo 0.1 e lo 0.5% (quindi inquadrabile come lega indurente per precipitazione)

Preliminary investigation by synchrotron radiation of small cracks and defects in AA FSW samples

A very good definition of defects position and dimension in welded joints is desirable for application of fracture mechanics techniques and improvement of industrial acceptability criteria. The aim of this paper is to illustrate the preliminary results achieved in the investigation of defects in aluminum welded joints, using the phase contrast X-ray imaging techniques available at the SYRMEP beamline of the Elettra synchrotron radiation facility. Both CCD and high-resolution X-ray films were employed as detection systems. Three sets of experiments have been performed so far. The aim of the first one was to investigate feasibility and to optimize the experimental set-up. A good definition of artifact defects on joints, obtained by both conventional welding techniques and Friction Stir Welding, was achieved. Successively, the investigation was restricted to joints obtained by Friction Stir Welding, which is currently the most interesting technique also from an industrial point of view. In the FSW samples prepared for the second experiment some original very small flaws were visible. The flaws size, 100 microns or more, makes them hardly detectable by means of conventional control methods. Further investigation of these small defects will provide a new unique insight on the defects that can be found in FSW samples. During the third experiment, that has not been finished yet, both a long and a small crack could be detected on the two sides of a notched sample. The images show that the crack propagates along several planes, a condition that has not been deeply investigated in a quantitative way up to now and will be the object of further investigation

Small cracks and defects in aluminium FSW samples: preliminary investigation by means of synchrotron radiation

Improvement of industrial acceptability criteria depends both on the verification of the defects visible with conventional techniques and the determination of the relationship between the residual life and the defect geometry, which in turn require a high definition of the defect dimension and position. While fracture mechanics is a well-established technique for relatively long cracks, very little is known at the moment relatively to the early development of small crack, that is the transition phase from the onset stage to the propagation stage of the crack growth. The assessment of fracture mechanics techniques for small crack problems depends strongly on a high definition of defect location and geometry. In order to overcome these problems, we started to investigate whether a good definition of defects position and dimension was achievable using the novel phase sensitive imaging techniques available at SYRMEP beamline, Elettra, with encouraging results

Preliminary results in the use of synchrotron radiation for small cracks and defects investigation in AA FSW samples

A very good definition of defects position and dimension in welded joints is desirable for application of fracture mechanics techniques and improvement of industrial acceptability criteria. This paper illustrates the preliminary results obtained in the investigation of defects in aluminum welded joints at SYRMEP beamline of the Elettra synchrotron radiation facility in Trieste (Italy). The novel PHase Contrast (PHC) imaging technique consents a definition of the defects better than the one achievable with conventional welded joints control methods such as ultrasonic techniques, acoustic emission and radiography

Preliminary investigation by synchrotron radiation of cracks and defects in AA FSW samples

A very good definition of defects position and dimension in welded joints is desirable for application of fracture mechanics techniques and improvement of industrial acceptability criteria. The aim of this paper is to illustrate the preliminary results achieved in the investigation of defects in aluminum welded joints, using the phase contrast X-ray imaging techniques available at SYRMEP beamline of the Elettra synchrotron radiation facility. Both CCD and high-resolution X-ray films were employed as detection systems. Three sets of experiments have been performed so far. The aim of the first one was to investigate feasibility and to optimize the experimental set-up. A good definition of artifact defects on joints, obtained by both conventional welding techniques and Friction Stir Welding, was achieved. Successively, the investigation was restricted to joints obtained by Friction Stir Welding, which is currently the most interesting technique also from an industrial point of view. In the FSW samples prepared for the second experiment some original very small flaws were visible. The flaws size makes the defects hardly detectable by means of conventional control methods. Further investigation will provide a new unique insight on the defects that can be found in FSW samples. During the third experiment, long and a small cracks could be detected on the sides of notched AA samples. A long crack is shown in Fig.1. The images and the tomographic reconstructions (as the one shown in Fig.2) show that the cracks propagates along several planes, a condition that has not been deeply investigated in a quantitative way up to now and will be the object of further investigation. Figure 1: PHC radiography of a long crack (extension approx 3.5 mm). Figure 2: PHC, 3D tomographic reconstruction of a crack (extension approx 1.24 mm)

Utilizzo della tomografia in luce di sincrotrone per la ricostruzione 3D di cricche

none6noneF. Cosmi; A. Cristofori; L. Mancini; R. Tovo; G. Tromba; M. VolponeF., Cosmi; Cristofori, Alessandro; L., Mancini; Tovo, Roberto; G., Tromba; M., Volpon