Ultrasonic Inspection Technique for Welded Joints Obtained by Spot Friction Stir Welding

Friction stir welding has found wide application in aircraft and rocket engineering, primarily due to the possibility of obtaining welded joints with a strength close to the strength of the base material. One of the most promising methods of such welding is spot friction stir welding that can serve as an alternative to electric contact spot welding and rivet joints. For the introduction of spot friction stir welding into the production of critical products, it is necessary to consider issues related to nondestructive quality control of welded joints obtained by this welding method. The purpose of this work is to substantiate the applicability of the ultrasonic echo method to quality control of welded joints obtained by spot friction stir welding. The relevance of the work is confirmed by the fact that to date there is no sufficiently complete information about the results of experimental studies aimed at analyzing the characteristics of welded joints obtained by spot friction stir welding. The authors of the article propose to use the ultrasonic echo method. The testing was carried out using an ultrasonic flaw detector with a dual-element piezoelectric transducer on samples prepared using spot friction stir welding. As a result of ultrasonic testing, defects such as lack of penetration and sloting were found in three samples; this was confirmed by metallographic studies. Samples with no defects were subjected to mechanical tests, as a result of which it was found that the strength of the resulting welded joints is comparable to the strength of the base metal in the samples. Metallographic studies carried out on the samples after mechanical tests also confirmed the lack of defects in the welded joints. Thus, we show the relationship between the results of ultrasonic testing, metallographic studies, and mechanical tests, which allows us to substantiate the applicability of the ultrasonic echo method to quality control of welded joints obtained by spot friction stir welding.