Nondestructive Testing And Defect Characterization Of Friction Stir Welding Joints Of Aluminum Alloys

Friction Stir Welding(FSW)and Refill Friction Stir Spot Welding(RFSSW)are widely used in high-strength aluminum alloy welding in the aerospace industry.However,due to improper setting of process parameters,poor surface condition of the material,and improper operation of the operator,defects such as incomplete penetration,tunnels,holes,and weak joints may exist in the FSW and RFSSW joints,thereby affecting joint performance.These defects are characterized by smallness,closeness and complexity.Therefore,effectively detecting these defects is a key factor in advancing the development of FSW and RFSSW technologies.For 6.5mm thick 2024 aluminum alloy FSW welded joints and 1mm+1mm lapped RFSSW joints,combined with common defects,using infiltration,X-ray and ultrasonic phased array methods to detect joint defects,and test results.Destructive testing results were compared and analyzed.By studying the influence of process parameters of infiltration,X-ray and ultrasonic phased array detection on defect detection results,combined with several detection methods to detect joint defects.The results show that the penetration test can successfully detect the incomplete penetration defects;the X-ray inspection can successfully detect the tunnel defects and inclusion defects;the ultrasonic phased array inspection can successfully detect the incomplete penetration defects,tunnel defects and inclusion defects,and.The penetration defects and tunnel defects are accurately located.The positioning error for the incomplete penetration defect is 2.5%;the positioning error for the tunnel defect is 3%.For RFSSW joints,the current non-destructive testing method cannot effectively characterize RFSSW joints because it can only be welded to specimens of no more than 2 mm.Among them,for the ultrasonic phased array detection,the detection signal strength on the retreating side of the FSW joint is stronger than that on the advancing side.It is because that the grain size of the heat affected zone and the thermo mechanically affected zone of the advancing side through which the ultrasonic wave mainly passes is large,and therefore the attenuation of the ultrasonic wave is large,and the detection will have worse performances.At the same time,the defect shape also has influences on the ultrasonic phased array detection.For example,the angle between the extension direction of the area type defects and the direction in which the ultrasonic wave is incident on the defects may cause changes to the detection signal.Therefore,the closer the angle between the defect and the ultrasonic wave are to 90°,the better the detection performances.Through a variety of detection methods combined with analysis,the type,shape and location of common defects in FSW joints can be successfully detected.