Support-enabled heat retention for activating in-situ heat treatment in laser powder bed fusion of high-strength aluminum alloys

In laser powder bed fusion (LPBF), support structures are conventionally used to anchor parts and mitigate distortion during fabrication. Here, we show that support structures can be engineered to control heat dissipation and harness intrinsic process heat for in-situ heat treatment (IHT) of precipitation-hardenable Al alloys. Using Scalmalloy® as a model system, preliminary process-parameter screening of unsupported samples showed that intrinsic process heat could produce only modest in-situ hardening at very high volumetric energy density, and this was accompanied by severe porosity. To overcome this density–hardness trade-off, low-area-fraction supports (LAFS) were introduced to promote IHT through reduced heat dissipation rather than excessive localized heat input. The use of LAFS was found to significantly prolong high-temperature exposure during layer-by-layer fabrication, thereby promoting substantial in-situ strengthening in the as-built state. Atom probe tomography revealed a high number density of Sc-rich clusters, which are identified as the dominant strengthening feature in the LAFS samples. By combining LAFS with interlayer time control, the hardness profile could be tailored to produce either gradient or near-uniform distributions. Tensile testing showed that the combined use of LAFS and a graded interlayer time strategy produced a yield strength of 453 MPa and an ultimate tensile strength of 479 MPa in the as-built state, achieving almost identical tensile performance to conventionally peak-aged Scalmalloy®. Multiscale thermal simulations established a quantitative link between local thermal histories and mechanical response through an equivalent aging framework. These results demonstrate the potential of using LAFS as a process-integrated tool for activating IHT in precipitation-hardenable Al alloys during LPBF without compromising densification, providing a practical route to reduce reliance on post-build heat treatment. © 2026 Elsevier B.V.