Ultrasonic inspection technology of welded joints obtained by spot friction welding

Abstract

Friction stir welding has found wide application in the aircraft and rocket industries, primarily due to the possibility of obtaining welded joints with a strength close to that of the base material. One of the most promising methods of such welding is friction stir spot welding, which can serve as an alternative to electric contact spot welding and riveting of joints. To introduce friction stir spot welding into the production of critical products, it is necessary to consider issues related to non-destructive 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 for quality control of welded joints obtained by friction stir spot welding. The relevance of the work is confirmed by the fact that today there is no sufficiently complete information on the results of experimental studies aimed at analyzing the characteristics of welded joints obtained by friction stir spot welding. The authors of the article proposed to use the ultrasonic echo method of control. The control was carried out using an ultrasonic flaw detector with a separate-combined piezoelectric transducer on samples of welds made using friction stir spot welding. Flaws such as lack of penetration and root sticking were found in three samples as a result of ultrasonic testing, which was confirmed by metallographic studies. Samples in which no defects were found were subjected to mechanical tests, as a result of which it was found that the strength of the obtained welded joints is comparable to the strength of the base metal of the samples. Metallographic studies were carried out on samples after the absence of defects in welded joints was confirmed through mechanical tests. Thus, the relationship between the results of ultrasonic testing, metallographic studies, and mechanical tests is shown, which makes it possible to justify the applicability of the ultrasonic echo method for quality control of welded joints obtained by friction stir spot welding.