Spectral diagnosis of wire arc additive manufacturing of Al alloys

Abstract

Online nondestructive testing for quality control is a critical direction for research in additive manufacturing in the future. In this study, for the first time, optical emission spectroscopy was employed to probe the arc characteristics in the wire arc additive manufacturing (WAAM) of an Al alloy and to detect its structural features. The arc characteristics, such as spectral intensity, electron density, and electron temperature, were calculated based on the atomic emission spectral lines. The resulting structural features of the deposited layers, namely the forming width, composition, grain size, and porosity defects, were analyzed, and a correlation between the arc characteristics and the structural features was proposed. The arc cathode size, which changed with the number of deposited layers, controlled the arc energy distribution. Hence, the forming width had an approximately linear relation with the spectral intensity of Mg (a constituent of the alloy used for the wire feed) and the electron density. The porosity in the alloy was observed to be caused by H, which was a dominant pollutant in the process. Furthermore, the correlation between the porosity and H spectral intensity was observed to be approximately linear. However, no significant correlation between the grain size and the spectrum was noticeable. The results from this study establish the applicability of spectral diagnosis of the forming size and the porosity in WAAM.