Suchergebnisse

Copyright © 2022 The Authors. Aluminium composites have been extensively developed for automotive applications due to their high specific strength. However, particle agglomeration, high porosity content, and weak reinforcement/matrix interface bond are prone to occur in the casting process. These arise during the introduction of the reinforcement, mould filling, and solidification process, especially when the particle sizes are approaching the nanoscale and are detrimental, with respect to the mechanical properties. By applying high pressure in conjunction with high cooling rates, an improved distribution of the reinforcing particles can be expected, as the high pressure improves the filling capacity of the composite melt, in which the fluidity is generally decreased by the added heterogeneous particles. The fine grain structure obtained under the high cooling rate is also beneficial for the distribution of the reinforcing nanoparticles during solidification. In this study, SiC nano-reinforced AlSi9Cu3 composites were developed by employing an Al–Cu-SiCnp master alloy, stir mixing, ultrasonication and HPDC technology. The findings showed a good distribution of individual SiC particles, resulting in a reduction of ∼40% in the α-Al grain size and near 10% increment in the yield strength, which was attributed to grain refinement, CTE strengthening and Orowan strengthening. Compared to commercial AlSi9Cu3 HPDC alloys, the developed AlSi9Cu3-1wt% SiCnp composite provided an improved YS of ∼187 MPa and a UTS of ∼350 MPa in the as-cast state and the milestone high YS and UTS of ∼370 MPa and ∼468 MPa under a T6 condition, respectively. ; Financial support from European Union (LIGHTME Grant Agreement No. 814552) is gratefully acknowledged. The authors are also grateful to the ETC for providing access to equipment for microstructural characterisation.

The mechanism underlying the considerable refinement of primary Al3Ti intermetallic particles induced by ultrasonic treatment (UST) in an Al-0.4 wt% Ti alloy in the fully liquid state was investigated. Scanning electron microscopy, energy dispersive X-ray spectroscopy, focused ion beam 3D tomography and transmission electron microscopy were used to clearly identify that α-Al2O3 particles were located at or near the centres of primary Al3Ti particles in the samples solidified with and without UST. Crystallographic evaluation using the edge-to-edge matching model and experimental determination of orientation relationships between the α-Al2O3 and primary Al3Ti particles using the convergent beam Kikuchi line diffraction patterns confirmed the high potency of α-Al2O3 particles as nucleation sites for the Al3Ti phase. Based on the experimental results, the refining mechanism is discussed in terms of proposed hypotheses in the literature. It is suggested that the significant refinement of primary Al3Ti particles upon UST is due to the cavitation-induced deagglomeration and distribution of the α-Al2O3 particles and the cavitation-enhanced wetting of the α-Al2O3 particles by liquid aluminium. ; The authors acknowledge the financial support from UK government's Engineering and Physical Science Research Council (EPSRC) for the Ultra-Cast project [Grant EP/L019884/1, EP/L019825/1, and EP/L019965/1].

Intensive melt shearing is a process that can be used for mixing ceramic particles into magnesium melt. It applies shear stress to the melt and can de-agglomerate nanoparticle additions to magnesium melts without the use of electromagnetic fields or ultrasound. A wrought magnesium alloy AM30 was selected for processing with intensive melt shearing and subsequent twin-roll casting. AM30 with additions of CaO and SiC were also processed by this route and the hardness and microstructure were investigated. Sheets were rolled and their tensile strength was determined. The work was done as part of the European Union research project ExoMet. Its target includes the production of high-performance magnesium-based materials by exploring novel grain refinement and nanoparticle addition in conjunction with melt treatment by means of external fields.