Material stirring and heat generation in friction\ud
stir welding processes induce significant microstructure\ud
and material properties alterations. Previous studies high-\ud
lighted the relationship among microstructure, grain size,\ud
microhardness, and performance of the joint. In this con-\ud
text, an opportune definition of process parameters, in\ud
particular rotating and welding speed, is crucial to improve\ud
joint reliability. In this article, results provided by a\ud
numerical and experimental investigation on the influence\ud
of rotating and welding speed on microstructure, mechan-\ud
ical properties, and joint quality in AA2024-T3 friction stir\ud
welded butt joints are reported. Experimental data are\ud
presented and discussed considering numerically computed\ud
temperature and strain rate distributions, providing useful\ud
information for parameters setting. Processing window,\ud
i.e., parameters resulting in a successful material deposi-\ud
tion, is also individuated
Sound AA2024-T3–Cu10100 dissimilar joints were obtained by friction stir welding offsetting the tool probe towards the aluminum sheet and employing selected processing parameters. Joint microstructure was analyzed by means of conventional optic microscopy as well as scanning electron microscopy. The weld bead exhibited welding zones and some features typically encountered in similar FSW. The nugget zone consisted of a mixture of recrystallized aluminum matrix and deformed and twinned copper particles. Onion rings and particle-rich zones, made of Cu particles dispersed in the Al matrix, were also observed. EDS analysis revealed that several Al–Cu intermetallic compounds, such as Al2Cu, AlCu, and Al3Cu4, chemically different w.r.t. compounds precipitated during the T3 aging treatment (Al3Cu), were formed during the process. Microstructure variation significantly affects the microhardness distribution in the cross-section of the join
Liquid composite molding processes are manufacturing techniques involving the impregnation and saturation of dry fibrous preforms by means of injection or infusion of catalyzed resin systems. Complete wetting of the reinforcement and reduction of voids are key issues to enhance mechanical properties of the final product, as a consequence on line monitoring and control of resin flow is highly desirable to detect and avoid potential macro- as well as micro-voids. In this paper, parallel-plate dielectric sensors were investigated to track the position of unsaturated as well as saturated flow fronts through dual scale porous media. Sensors configuration was analyzed and improved via electromagnetic (EM) finite element simulations. The effectiveness of the proposed system was assessed in one-dimensional impregnation tests. Good agreement was found between unsaturated front positions provided by the considered system and acquired through conventional visual techniques. An indirect verification strategy, based on CFD and EM simulations of the process, was applied to investigate the reliability of dielectric sensors with respect to saturation phenomena. Obtained outcomes highlighted the intriguing capabilities of the proposed method
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