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Santos T.G.,New University of Lisbon | Santos T.G.,Institute Engineering Mecanica Polo IST | Vilaa P.,Institute Engineering Mecanica Polo IST | Vilaa P.,University of Lisbon | And 2 more authors.
Journal of Materials Processing Technology | Year: 2011

To fully characterize Friction Stir Welding several techniques are required, mainly destructive, as hardness or metallographic testing. However, there is still a need for developing dedicated methods, preferably non-destructive. Electrical conductivity, based on a different physical principle, may constitute an alternative. The present study aims to characterize the electrical conductivity in friction stir welds and to investigate the correlation between this and the hardness observed in different regions of a weld. An eddy current planar probe was used for the measurements at different depths. For this, welded samples were machined in steps and in ramp and scans along orthogonal axis were performed. The results were correlated with the microstructural modifications. A close match between the electrical conductivity field and the microstructure was observed. A good correlation with hardness was noticed, suggesting that the non-destructive test has the potential to complement or substitute destructive methods as hardness tests. © 2010 Elsevier B.V. All rights reserved.

Santos T.G.,New University of Lisbon | Miranda R.M.,New University of Lisbon | Vilaca P.,Institute Engineering Mecanica Polo IST | Vilaca P.,University of Lisbon
Annals of "Dunarea de Jos" University of Galati, Fascicle XII, Welding Equipment and Technology | Year: 2011

This study aims to present research work that demonstrates the beneficial use of the electrical conductivity measurements to evaluate the extent of structural modifications in the different zones of Friction Stir welds. The results were compared to microhardness profiles of transverse sections and the structural modifications were observed by optical microscopy. A good fit between the electrical conductivity field, the microhardness profile and the microstructure was observed, suggesting a potential use of electrical conductivity to assess structural modifications substituting hardness. © Galati University Press, 2011.

Santos T.G.,New University of Lisbon | Faria J.,New University of Lisbon | Vilaca P.,Institute Engineering Mecanica Polo IST | Miranda R.M.,New University of Lisbon
Materials Science Forum | Year: 2013

Eddy currents are based on electromagnetic induction and analysis of electrical currents on conductive materials. This method is used for thickness measurements, corrosion and defects detection, electrical conductivity and magnetic permeability measurements. Recently, it has been exploited as a materials characterization technique, namely in solid state welding, since, compared to hardness, it is based in distinct physical phenomena. Electrical conductivity is controlled by electronic mobility, while hardness depends on crystal defects and thus a scale factor exists. This paper presents results of this characterization technique applied to multipass solid state friction stir processing (FSP) of AA1100 alloy. These results were compared to microstructural analysis and hardness measurements and show that eddy current is a feasibly, reliable and expedite technique to characterize processed materials. The electrical conductivity measured by eddy currents, maps more precisely structural features, while hardness does not. Measurement of electrical conductivity field suggests having potential to constitute an alternative and/or complement to hardness evaluation with the further advantage of being a non-destructive method. © (2013) Trans Tech Publications, Switzerland.

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