The significance of supplementary shielding in WAAM of aluminium thin walls

WAAM (wire arc additive manufacturing) of aluminium requires special operational care to avoid problems such as instabilities, contamination or porosities. This work aims at verifying whether supplementary shielding gas can affect the WAAM performance when building Al alloy thin walls, in terms of metal transfer, porosity, superficial finishing, and geometrical and metallurgical features. Thin walls were manufactured with and without supplementary shielding (ultra-pure Ar). A dedicated nozzle was designed in-house to provide additional protection against the reaction with surrounding atmospheric gases. Pure Ar and two Ar-based commercial shielding gases with different additives were employed to make the conclusions more sustainable. It was possible to conclude that supplementary shielding leads to better metal transfer regularity, cleaner lateral and surface, a shinier top layer appearance, and a slight trend to higher microhardness. On the other hand, it does not affect porosity after layer depositions, wall geometry (the total and effective layer width, layer height, and surface waviness of the walls), and microstructures. Finally, regarding the performance of shielding gases, there is no evidence of any effect from the supplementary shielding, since this approach improved the process operationality with the three different shielding gases but did not change their individual tendencies.