EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Laser beam melting is a powder bed additive manufacturing process, allowing the fabrication of complex parts from 3D models. For each layer, powder is spread on building platform and particles are melted following the model by laser scanning. AlSi10Mg is a heat treatable alloy generally processed by casting, widely employed for transportation applications. This grade is one of the most used thanks to good foundry behavior. Parts properties depend on process parameters, such as building strategies and preheating temperature. The latter is fixed whether cold to exploit the ageing potential of supersaturated solution with subsequent artificial ageing or warm to minimize thermal stresses.
The study aimed to highlight the effect of building platform preheating (170°C) on the microstructural and mechanical properties of parts manufactured in different platform areas, at various heights and in multiple orientations. Microstructural analyses, Charpy, hardness and tensile tests confirmed different properties between axis parallel and perpendicular to the building direction: fracture energies and elongation are higher for samples built horizontally. Moreover, a gradient of fracture energy and hardness over the manufacturing height is also revealed. The closer the sample is to the platform, the higher its fracture energy and the lower its hardness. The hardness gradient exhibited the shape of an ageing curve as a function of height. Samples located close to the platform borders showed higher hardness values in both directions in comparison with center samples. The latters displayed higher fracture energies only for horizontal building orientation. These results were linked to the inhomogeneous heat dissipation and to an in situ heat treatment caused by preheating. Multiple post-fabrication ageing of the furthest parts from the platform made it possible to recover the hardness gradient over height. Finally, the anisotropic behavior is accompanied by properties gradients within the platform and on height with preheating.