Targeting low micro-roughness for 3D printed aluminium mirrors using a hot isostatic press

Additive manufacturing (AM) in aluminium using laser powder bed fusion provides a new design space for lightweight mirror production. However, internal porosity, a common AM defect, results increased scattered light from the reflective surface of the AM mirror. One strategy to reduce porosity is to apply a hot isostatic press (HIP) to the part after printing. This paper presents the results of balancing the ability of HIP to reduce porosity in aluminium samples with its ability to promote grain growth, which has a negative impact when generating the reflective surface. The impact of HIP is assessed using x-ray computed tomography, micro-roughness measurements, mechanical testing, and electro backscatter diffraction.