Effect of interlayer coating La2O3 particles on arc behavior and microstructure of wire arc additive manufacturing Al-Si alloy deposition

In this paper, three kinds of ER4043 aluminum alloy depositions with the interlayer coating La2O3 particles were successfully fabricated by cold metal transfer (CMT) wire arc additive manufacturing (WAAM) technology, and the evolution of various La2O3 particles size on arc behavior, forming defects, microstructure and mechanical properties was described. The results indicated that arc length and horizontal diameter of the CMT-WAAM specimens were directly related to the size of coating La2O3 particles. When the interlayer was coated ordinary and micron-sized La2O3 particles, the violent arc fluctuations and welding spatter were generated and deteriorated forming quality. When the interlayer was coated nano-sized La2O3 particles, the proper arc deflection could improve the fluidity of the molten pool and promote the stomas escape to obtain excellent forming quality. The tensile strength in both horizontal and vertical directions increased to 209.17 MPa and 165.34 MPa, which were 22.55 % and 15.82 % higher than that of the additive specimen without coated powder, respectively. A majority of La2O3 particles were existed in grain boundaries in a form of like-eutectic. Additionally, some of dissociated La2O3 particles became heterogeneous nucleation sites and were included in the Al matrix. This process of interlayer coating nano-sized La2O3 provided more nucleation masses and further refined microstructure of the WAAM specimens during the solidification. The results from this study provided an essential reference to introduce rare earth oxides into deposited interlayer and improve the mechanical properties of CMT-WAAM depositions.