Superficial and subsuperficial compositional and microstructural modification of additive manufactured AlSi10Mg via low-power, low speed laser surface remelting

Abstract

The introduction of additive manufacturing technologies, in their various forms, has opened new possibilities for the design and fabrication of optomechanical components with superior performance and characteristics compared to those produced through conventional manufacturing procedures. Although excellent preliminary results have been reported -particularly in terms of mass reduction and component consolidation- several challenges remain, particularly when these technologies are applied to the fabrication of reflective optical elements (mirrors). These challenges, inherent to metal-based additive manufacturing processes, primarily manifest as open (surface) and closed (internal) porosity, microstructural heterogeneity, and discontinuities within the grain matrix. Such features result in a lack of material homogeneity that severely affects subsequent high-precision manufacturing procedures such as Single Point Diamond Turning, required to achieve the final specular surface. This study investigates the use of low-power and slow traversing speed laser source under a controlled vacuum atmosphere in order to produce a deep superficial remelting to homogenize the upper layers of additively manufactured AlSi10Mg coupon blanks. The approach aims to refine the microstructure, reduce porosity, and mitigate chemical and morphological discontinuities that hinder the production of optical-grade surfaces, significantly enhancing the overall homogeneity of the top layers of the base material, thereby facilitating subsequent mechanical figuring operations. The resulting microstructural and mechanical modifications are evaluated through melt pool geometry, residual porosity quantification, compositional analysis, hardness measurements, and metallographic inspection. Additionally, it provides further information on the mechanism of process-induced porosity formation over a wide range of vacuum pressures, as well as presenting a simple, cost-effective method for its measurement.