The thermal conductivity of AlSi10Mg made by laser powder bed fusion (LPBF), and its modification via heat treatment, has received little attention despite possible applications for heat exchangers and thermo-mechanical components. Here, we show that heat treatment can increase the thermal conductivity of LPBF AlSi10Mg to that of cast material. Our results indicate that post-manufacture annealing eliminates the thermal conductivity anisotropy present in the as-built condition, and enhances the conductivity by close to 30 % in the transverse direction (perpendicular to the LPBF build orientation). A solution heat treatment increases the thermal conductivity further still (36 % compared to the as-built condition), while a T6-like treatment provides the greatest increase (44 % compared to the as-built condition). These improvements are related to the evolution of the AlSi10Mg microstructure, especially the breakdown of the Si cellular structure. Additionally, the thermal conductivities of gyroid lattice structures were examined in the as-built and annealed conditions. Contrary to solid specimens, the lattice structures exhibited almost isotropic thermal conductivity in the as-built condition. Their thermal conductivities were increased by the annealing treatment in proportion to their volume fraction. Our findings contribute to the development of a general design-for-additive-manufacturing (DfAM) framework which will make the best possible use of AM materials and lattice structures for heat transfer components.

Additive manufacturing (AM) has the capability to build complex parts with internal features, which have many advantages over conventionally manufactured parts. This makes AM an alternative for advanced manufacturing sectors. AM components suffer from defects due to the lack of understanding in the build process. This makes the adaptation of AM in safety-critical industries, such as aerospace, problematic. The current AM work flow calls for costly off-line inspections to qualify components as defect-free. The layer by layer nature of the AM provides an opportunity for an on-line inspection to take place. This can provide early detection of defects as well as information for optimization and repair of the build. Laser Induced Phased Arrays (LIPA) present themselves as a viable remote, non-destructive, ultrasonic technique capable of being implemented as part of an on-line inspection of AM. Lasers are used to generate and detect ultrasound and a phased array is synthesized in post-processing. This paper demonstrates the capability of LIPA to successfully detect and locate features within AM components off-line. Cylindrical features as small as 0.2 mm in diameter and 26 mm above the inspection surface were detected using LIPA and verified using X-ray computed tomography (XCT).

In this study, the melt pool (MP) morphology evolution (solidification) in a Hilbert fractal pattern for the Powder-Bed Fusion Additive Manufacturing (PBF-AM) of Alloy 718 is examined by devising a 'Unit Cell' Methodology (UCM). Since scan strategies are becoming an increasingly important method for managing morphological, microstructural phenomena, and thermally induced stresses, new scan strategies are a requirement. The methodology described here involves defining a 'unit cell' from the larger (higher-order) Hilbert fractal curve and then printing the constitutive lines (vectors) of the 'unit Hilbert cell' and visualising its morphological evolution over a single layer. Process parameters (line length of the 'unit cell,' laser power, and laser speed) variations are performed to analyse its effects on the morphology of the 'unit Hilbert cell' (single layer). The higher-order Hilbert fractal curve is then demonstrated in stages to explain the morphological evolution. The observed coalesced MP propagates over the surface in the larger (higher-order) Hilbert fractal curve, according to the position of the 'unit cells' in the Hilbert fractal curve. The flow of a coalesced MP in PBF-AM using the short vector lengths at a lower linear energy density and three times the width of parallel-line single-track MPs is demonstrated for the first time with the Hilbert fractal. Process parameter variation on the 'unit Hilbert cell' results in MP morphology (dimensions and shape) changes. These variations help to choose the required coalesced MP dimensions in the higher-order Hilbert fractal and ensure good hatching with the adjacent 'unit cell' MPs as it propagates. The proposed methodology could be expanded to allow an understanding of the morphology evolution of other fractal curves in the PBF-AM process.