Thermographic detectability of porosity in multi-layered bare and anodized aluminum laser welds

This study investigates porosity detection by means of thermography in multi-layered laser welded aluminum joints. Samples with varying levels of porosity were created by laser welding bare or anodized aluminum material in multiple layers. For comparison, two Al 1100 top layer materials, one anodized and one bare, were welded in multiple layer configurations onto a 1.6 mm Al substrate. The samples were characterized by electrical measurements, tensile tests, and X-ray computed tomography imaging. Thermography was performed on the entire sample set, where the heat source distribution was used to analyze raw thermal data corresponding to the weld region-of-interest. A maximum peak histogram value of the thermography data was determined and was found to correlate well with the X-ray CT, electrical resistance, and tensile data. Thermography was observed to be more affected by pores close to the surface as confirmed by the porosity cross sections from the CT data. It was seen however, that in areas of many small pores, the overall thermography values indicated lower heat flow than other areas even if the individual pores could not be resolved. Overall it is shown that thermography correlates well with electrical resistance and tensile results, although more studies are needed to evaluate thicker stack-ups due to the limits placed by thermal diffusion. (c) 2020 The Authors. Published by Elsevier B. V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under the responsibility of the scientific committee of NAMRI/SME