Effect of nanoparticle-based activated TIG remelting on ground PWAAM Al–Cu–Si alloy deposits using DC current

Abstract

Plasma wire arc additive manufacturing (PWAAM) enables the production of aluminium based in-situ alloys using multiple wire feeds, but with incomplete solution, that is, retained Cu rich regions and microstructural heterogeneity may occur due to the different melting behaviour of the alloying elements. In this study, ground PWAAM Al–Cu–Si alloy deposits were remelted using conventional TIG remelting and activated TIG remelting at a current of 173 A. The aim was to investigate the influence of nanoparticle based activating fluxes on remelted zone geometry, microstructure and microhardness. Three fluxes, based on 20 nm TiO₂, 40 nm SiO₂ and 5 nm SiO₂ nanoparticles, were compared with flux free TIG remelting. The results showed that the activating flux affected penetration depth, remelted width and thereby remelted area. The 40 nm SiO₂ flux produced the largest remelted zone, while the 20 nm TiO₂ flux resulted in the most pronounced microstructural refinement. The 5 nm SiO₂ flux also increased the remelted area compared with flux free remelting, although retained Cu-rich particles were still observed locally. All investigated ground specimens exhibited relatively low porosity. Microhardness measurements showed increased values within the remelted regions, with the highest hardness obtained in the TiO₂-assisted specimen. The results indicate that DC activated TIG remelting of ground PWAAM Al–Cu–Si deposits can be used to modify remelted zone geometry and improve local microstructural and hardness characteristics.