The measurement of weld morphology and inclusions using ultrasonics

Abstract

The morphology of welding pool (fusion zone and heat affected zone) includes a variety of microstructural constitutions (the formation of new boundaries, pores, and textures) that can affect the integrity of welded joint. Currently, microscopic observations are the common method to characterize the welding pool, which is a destructive post-welding procedure, and requires a complex preparation process. In this paper, linear and non-linear ultrasonic methods are investigated to measure the weld morphology and the presence of porosity nondestructively in welds manufactured with gas tungsten arc welding (GTAW). The weld morphology and the presence of porosity are quantified using microscopic investigations. The measurements show that the ultrasonic energy obtained by linear ultrasonics and the acoustic nonlinearity parameter obtained by nonlinear ultrasonics have good correlation with the weld morphology. The relationship between the ultrasonic energy and the weld morphology is validated further with numerical models. The linear UT at 1 MHz is not sensitive to the presence of porosity as the resolution is limited by ultrasonic wavelength. However, nonlinear ultrasonics has better sensitivity to the inclusions due to sub-wavelength resolution.