Friction stir processing

About: Friction stir processing is a research topic. Over the lifetime, 2977 publications have been published within this topic receiving 62158 citations.

Transient Heat and Material Flow Modeling of Friction Stir Processing of Magnesium Alloy using Threaded Tool

Abstract: A three-dimensional transient computational fluid dynamics (CFD) model was developed to investigate the material flow and heat transfer during friction stir processing (FSP) in an AZ31B magnesium alloy. The material was assumed to be a non-Newtonian viscoplastic fluid, and the Zener-Hollomon parameter was used to describe the dependence of material viscosity on temperature and strain rate. The material constants used in the constitutive equation were determined experimentally from compression tests of the AZ31B Mg alloy under a wide range of strain rates and temperatures. A dynamic mesh method, combining both Lagrangian and Eulerian formulations, was used to capture the material flow induced by the movement of the threaded tool pin. Massless inert particles were embedded in the simulation domain to track the detailed history of material flow. The actual FSP was also carried out on a wrought Mg plate where temperature profiles were recorded by embedding thermocouples. The predicted transient temperature history was found to be consistent with that measured during FSP. Finally, the influence of the thread on the simulated results of thermal history and material flow was studied by comparing two models: one with threaded pin and the other with smooth pin surface.

Damage mechanisms in selective laser melted AlSi10Mg under as built and different post-treatment conditions

Abstract: Selective laser melting (SLM) manufactured AlSi10Mg alloys present a fine silicon-rich network and precipitates which grant high mechanical strength but low ductility. Post-treatments, aiming at eliminating inherent defects related to SLM such as residual stresses, porosity or inhomogeneity, result in significant changes in the microstructure and impact both the hardening and the damage mechanisms of the post-treated material. The present work is dedicated to the investigation of the fracture of SLM AlSi10Mg under as built and three post-treatment conditions, namely two stress relieve heat treatments and friction stir processing (FSP). It is found that the interconnected Si network fosters damage at low strain due to the brittleness of the Si phase. The onset of damage transfers load to the enclosed Al phase which then fractures quickly under high stress, thus leading to low material ductility. In contrast, when the Si network is globularized into Si particles, the ductility is highly increased even in the case where the porosity and inhomogeneity of the microstructure remain after the post-treatment. The ductility enhancement results from the delay in void nucleation on the Si particles as well as from the tolerance for void growth in the Al matrix.

Fabrication of in situ carbon fiber/aluminum composites via friction stir processing: Evaluation of microstructural, mechanical and tribological behaviors

Abstract: Carbon fiber reinforced AA5052 bulk composites were successfully fabricated by multi-pass friction stir processing (FSP), aiming to improve the wear-resistance of AA5052. The microstructural, mechanical and tribological performances of the composites were documented and investigated. Microstructure observations indicated that, in the composites, carbon fibers were homogeneously dispersed in large volume, where no obvious Al4C3 layer was detected between the matrix and the carbon fibers. The orientation of carbon fibers in the composites were random owing to the severe plastic deformation brought on by FSP. Further mechanical tests showed that the hardness of the composites increased by 46.8% comparing to the base metal, and that the composite fabricated at 1000 rpm and 75 mm/min showed 18.6% higher UTS and 13.0% higher elongation in comparison with the base metal. The wear tests illustrated that wear process of the composites was more stable and the wear volume loss was reduced by more than 70%. The strengthening of mechanical properties was attributed to formation of GNDs, crack deflection and load transfer of carbon fibers. The further analysis on the worn surfaces revealed that abrasive wear occurred in the composites, while adhesive wear occurred in both the based metal and FSPed matrix. The addition of carbon fibers segments in the aluminum could suppress the nucleation and propagation of micro-cracks, which effectively prevented the material peeling during the wear process and thus improved the tribological properties. In addition, the formation of mechanical mixing layer would be another contributing factor to the improvement of wear resistance.