Investigation on surface morphology and microstructure of double-wire + arc additive manufactured aluminum alloys based on spectral analysis

Abstract

Double-wire + arc additive manufacturing has gained increasing attention due to the advantage of controlling alloy composition in real time. However, the control mechanisms of microstructure and mechanical properties of high strength aluminum alloys have not been revealed. To solve this problem, in-situ monitoring of double-wire + arc additive manufacturing process were carried out by the spectrograph and a visual sensor. The spectral signal and arc plasma characteristics under different wire feeding rate ratios were systematically studied. Combined with the high-speed photography results of the droplet transfer, it was found that spectral intensities of Mg I 517.26 nm represented abnormally high during the globular transfer process. Surface bulges with the size of about 100 μm were detected. In addition, the microstructure and phase composition of the deposited parts were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results indicated that the variation of electron temperature was consistent with the variation trend of Al2CuMg phase content under different processes. The intensity ratio IRMn/Mg of spectral line Mn I 407.92 nm to Mg I 517.26 nm was proposed to quantitatively measure the degree of phase transformation, which had a better performance than the spectral line intensity and electron temperature. Under the conditions of this research, the phase composition was α(Al) + θ(Al2Cu) + S(Al2CuMg) three-phase when the IRMn/Mg fluctuated around 0.59, and α(Al) + S(Al2CuMg) two-phase produced when the IRMn/Mg fluctuated around 0.35.