Strategies to Reduce Porosity in Al-Mg WAAM Parts and Their Impact on Mechanical Properties

Abstract

With the advent of disruptive additive manufacturing (AM), there is an increasing interest and demand of high mechanical property aluminium parts built directly by these technologies. This has led to the need for continuous improvement of AM technologies and processes to obtain the best properties in aluminium samples and develop new alloys. This study has demonstrated that porosity can be reduced below 0.035% in area in Al-Mg samples manufactured by CMT-based WAAM with commercial filler metal wires by selecting the correct shielding gas, gas flow rate, and deposition strategy (hatching or circling). Three phase Ar+O2+N2O mixtures (Stargold®) are favourable when the hatching deposition strategy is applied leading to wall thickness around 6 mm. The application of circling strategy (torch movement with overlapped circles along the welding direction) enables the even build-up of layers with slightly thicker thickness (8 mm). In this case, Ar shielding gas can effectively reduce porosity if proper flow is provided through the torch. Reduced gas flows (lower than 30 Lmin) enhance porosity, especially in long tracks (longer than 90 mm) due to local heat accumulation. Surprisingly, rather high porosity levels (up to 2.86 area %) obtained in the worst conditions, had a reduced impact on the static tensile test mechanical properties, and yield stress over 110 MPa, tensile strength over 270 MPa, and elongation larger than 27% were achieved either for Ar circling, Ar hatching, or Stargold® hatching building conditions. In all cases anisotropy was lower than 11%, and this was reduced to 9% for the most appropriate shielding conditions. Current results show that due to the selected layer height and deposition parameters there was a complete re-melting of the previous layer and a thermal treatment on the prior bottom layer that refined the grain size removing the original dendritic and elongated structure. Under these conditions, the minimum reported anisotropy levels can be achieved.

Shielding gas influence on AA5086 welded joints: residual stresses analysis, microstructural characterisation and mechanical properties

“…Additionally, Arana et al [15] also observed that argon generated greater porosity area percentage compared to a three-phase mixture Ar +O 2 + N 2 O mixture considering the same shielding gas ow rate and deposition strategy in the wire-arc additive manufacturing (WAAM) process with ER5356 ller metal.…”

A Brief Review on The Common Defects in Wire Arc Additive Manufacturing

“…Existence of Porosity is one of crucial troubles in WAAM process, which can reduce the overall density of the produced parts and thus severely harm the mechanical properties of the fabricated components [59,86,87]. Pores can be mainly sorted into small and homogenously distributed hydrogen pores, with a diameter size up to 100 µm, and into big and in homogeneously distributed process pores [87].…”

“…Pores can be mainly sorted into small and homogenously distributed hydrogen pores, with a diameter size up to 100 µm, and into big and in homogeneously distributed process pores [87]. Porosity is generated by various reasons including type of the used arc welding process, process parameters, inter pass temperature, wire alloy composition and quality [59]. PN Anyalebechi [88], explained that gas porosity is usually caused by two concomitant mechanisms, namely, volumetric shrinkage and the change in the solubility and associated precipitation of hydrogen during solidification.…”

Wire Arc Additive Manufacturing Of 5356 Aluminum Alloy

“…Tensile test specimens were prepared by wire erosion cutting method in accordance with ISO 6892-1-2009 standard [20]. Tensile samples are taken parallel and perpendicular to the weld direction and part taken for microstructure and microhardness analysis [21,22]. For microstructure and microhardness analysis, a piece was taken from the middle of the tensile samples.…”