Investigation of dissimilar metal joints with nanoparticle fillers

摘要

There is high demand for lightweight but strong materials, which has brought about hybrid structures that are made from dissimilar light materials such as aluminium alloys. Friction stir welding (FSW) can be used not only for the joining of dissimilar materials but to produce structures with enhanced properties by incorporating reinforcing fillers (e.g., SiC) into the weld. The quality of welds produced using FSW can be affected by imperfect welding process parameters or uncontrollable variables. The objective of this work was the application and verification of a high-frequency ultrasonic technique for the investigation of dissimilar metal joint quality. Four welds with different numbers of friction stir processing passes were investigated using macroscopic study, acoustic microscopy (AM), and X-ray computed tomography (CT) techniques. Image fusion of the AM and CT results are presented, and these confirm the images obtained with the acoustic microscope correlate well with the X-ray CT. Investigations demonstrate that scanning acoustic microscopy can show even the smallest voids, their position, and their size in the weld. It was shown that number and the direction of passes influence the quality of the weld considerably. The presented results prove that the macrostructural study is not sufficient to evaluate the quality of the friction stir weld.