Laser-Based Closed-Loop Controlled Heat Treatment for Residual Stress Relief of Additively Manufactured AlSi10Mg Components

Abstract

In laser powder bed fusion of metals small melt pools with extremely short solidification times and steep temperature gradients to the surrounding material exist due to the layer-wise and selective melting process with small areas of energy input compared to the cooler, solid ambient material. This causes high thermally induced residual stresses (RS), which can lead to the immediate rejection of the component due to critical part deformation and inhomogeneous mechanical properties under load. To prevent this, furnace-based stress relief heat treatments are commonly applied before cutting-off the part from the built platform. In this study a novel closed-loop controlled laser-based heat treatment using temperature feedback through inline pyrometer measurement is investigated, enabling a fast and highly efficient postprocess stress relief. Therefore, a laser beam is guided by a scanner optics in a meandering pattern over the top surface of AlSi10Mg cantilever specimens. It enables a decrease of near-surface RS from 158 to 5 N mm−2, resulting in a reduction of displacement by over 90% at material affecting depths up to 3 mm and area rates of 8 to 163 mm2 s−1.