Effect of Hot Isostatic Pressing and heat treatments on porosity of Wire Arc Additive Manufactured Al 2319

Abstract

Porosity and lack of fusion defects that can occur during additive manufacturing are often managed with Hot Isostatic Pressing (HIP). However, the thermal conditions experienced during the HIP cycle may create undesirable phases in some alloys and post HIP heat treatments including solution treatment + ageing may be necessary to achieve the desired final properties. It is currently unknown whether post-HIP heat treatments at standard atmospheric pressures promote the re-emergence of previously closed porosity in aluminium alloys produced by Wire Arc Additive Manufacturing (WAAM). Using micro 3D computed tomography, this work quantitatively investigates the extent of pore regrowth during post-HIP solution treatment and ageing of Al 2319 produced by WAAM. It is found that large porosity (diameters > 35 µm) that is closed during HIP mostly remain closed during subsequent heat treatment but almost a 3-fold increase in the frequency of fine gas porosity occurs during post HIP heat treatment. However, the overall porosity distribution after post HIP heat treatment remains up to 95 % lower than in the original as-built condition, indicating that HIP + heat treatments remain a viable pathway for defect reduction in industrial products.