Fusion-diffusion electron beam welding of aluminum‑lithium alloy with Cu nano-coating

Abstract As a new method to reduce the temperature in melt pool and subsequently alleviate the Li evaporation loss, fusion-diffusion electron beam welding is proposed for aluminum‑lithium alloy joining achieved by defocused electron beam and pressure. The Li evaporation loss, which was only 9%, was significantly suppressed compared to the ordinary electron beam welding. However, joining failed within the unfused region due to the poor atomic diffusion. As a result, Cu nano-coating, with a 300 nm thickness, was sputtered to the butt surface of base metal to accelerate atomic diffusion. After adding Cu nano-coating, the unfused region achieved an effective joining since the eutectic α-Al + Al2Cu appeared at 821 K, indicating that an equiaxed crystal zone, which joined two base metals, was formed at unfused region. Reasons for the presence of equiaxed crystal zone were examined. Dispersed strengthening phases including θ′ (Al2Cu) and T1 (Al2CuLi) were observed to be present in both the fusion zone and equiaxed crystal zone, corresponding to a higher tensile strength and increased hardness value in equiaxed crystal zone.