Friction stir processing of AlSi10Mg parts produced by selective laser melting

The additive manufacturing (AM) of aluminum alloys promises a performance enhancement of lightweight parts produced using Selective Laser Melting (SLM). Post-processing for AM parts produced using SLM is often an essential step homogenizing their microstructure and reducing as-built defects. In this study, friction stir processing (FSP) was used as a localized treatment on a large surface area of AlSi10Mg parts using multiple FSP tool passes. The influence of FSP on the microstructure, hardness, and residual stresses of both as-built and hot isostatic pressed (HIPed) parts were investigated. FSP transforms the microstructure of parts into an equiaxed grain structure. Microstructure homogenization was achieved consistently over the processed surface after applying a high ratio of tool pass overlap ≥ 60%. FSP of the as-built sample results in the breaking up of the fibrous Si network into nano-scale particles, leading to a more homogeneous distribution of nano-scale Si particles with a subsequent microhardness increase as compared to the HIP + FSP sample. The normal residual stresses measured on the FSP + as-built surface are lower, as compared to the HIP + FSP surface. A microstructure and hardness map was prepared to assist in selecting the optimum FSP parameters needed to achieve the required quality of the final processed parts. This study concludes that FSP could be used as a localized surface treatment to improve the microstructure of both as-built and HIPed AlSi10Mg parts fabricated using SLM.