Development of AlSi10Mg-AlN Metal Matrix Composites for Laser Powder Bed Fusion Additive Manufacturing
Abstract
AlSi10Mg is an aluminum alloy widely utilized in additive manufacturing (AM) due to its favorable response to processing and high strength-to-weight ratio. However, its stiffness, thermal conductivity, and thermal stability are insufficient for certain applications. To address these limitations, researchers have investigated the incorporation of controlled levels of ceramic particulate into the alloy. This study focuses on the influence of aluminum nitride (AlN) additions on the processability of AlSi10Mg using laser powder bed fusion. A design of experiments (DOE) approach was employed to analyze the effects of various parameters, including AlN concentration, laser power, scan speed, and hatch spacing, on the density of the final parts. The study established an effective processing window and used favorable parameter combinations to fabricate additional specimens for a comprehensive assessment of microstructure, matrix/ceramic interfaces, mechanical properties, and thermal properties.
An initial central composite design (CCD) revealed that laser power had the most significant impact on specimen density among the investigated parameters. Poor consolidation was observed when the laser power was set at or below 150W, regardless of the total volumetric energy density (VED). The occurrence of irregular lack of fusion (LOF) pores increased in terms of quantity and size outside the optimal VED range. An additional DOE demonstrated that the optimal VED range for all chemistries was 60-80 J/mm3. However, for metal matrix composites (MMCs) with increased laser absorptivity, operating at a lower power and scan speed within this VED range could be advantageous.
A comparison between 0% AlN and 5% AlN-F specimens, fabricated using optimized tensile parameters (Laser power = 240W, scan speed = 1000mm/s, hatch spacing = 0.10mm), revealed increased gas porosity in the MMC specimens. This is attributed to the lower thermal diffusivity in the MMC powder bed, resulting in higher localized temperatures and increased vaporization. Tensile testing indicated improved elongation in the AlSi10Mg alloy following a stress-relief heat treatment, although yield strength (YS) and ultimate tensile strength (UTS) were compromised. Despite lower density, the stress-relieved MMC demonstrated YS and UTS comparable to those of the stress-relieved AlSi10Mg alloy.