Fabrication of metal matrix composites under intensive shearing

Current processing methods for metal matrix composites (MMC) often produces agglomerated reinforced particles in the ductile matrix and also form unwanted brittle secondary phases due to chemical reaction between matrix and the reinforcement. As a result they exhibit extremely low ductility. In addition to the low ductility, the current processing methods are not economical for producing engineering components. In this paper we demonstrate that these problems can be solved to a certain extent by a novel rheo-process. The key step in this process is application of sufficient shear stress on particulate clusters embedded in liquid metal to overcome the average cohesive force of the clusters. Very high shear stress can be achieved by using the specially designed twin-screw machine, developed at Brunel University, in which the liquid undergoes high shear stress and high intensity of turbulence. Experiments with Al alloys and SiC reinforcement reveal that, under high shear stress and turbulence conditions Al liquid penetrates into the clusters and disperse the individual particle within the cluster, thus leading to a uniform microstructure

Processing of advanced Al/SiC particulate metal matrix composites under intensive shearing – A novel rheo process

Particulate Metal Matrix Composites (PMMCs) have attracted interest for application in numerous fields. The current processing methods often produce agglomerated particles in the ductile matrix and as a result these composites exhibit extremely low ductility. The key idea to solve the current problem is to adopt a novel Rheo-process allowing the application of sufficient shear stress () on particulate clusters embedded in liquid metal to overcome the average cohesive force or the tensile strength of the cluster. In this study, cast A356/SiCp composites were produced using a conventional stir casting technique and a novel Rheo-process. The microstructure and properties were evaluated. The adopted Rheo-process significantly improved the distribution of the reinforcement in the matrix. A good combination of improved Ultimate Tensile Strength (UTS) and tensile elongation (ε) is obtained

In-situ microstructural control of A6082 alloy to modify second phase particles by melt conditioned direct chill (MC-DC) casting process - A novel approach

© 2021 The Authors. Controlling the formation of noncompact second phase particles during direct chill (DC) casting of aluminium alloys with grain refiner addition remains challenging, as it results in energy intensive homogenisation and deformation problems. In this work, we employed a novel strategy in the DC casting of A6082 alloy to produce billets with a fine-scale dispersion of second phase particles. The strategy involves maintaining 2–7 °C above alloy liquidus as a thermal condition in the sump by in-situ melt conditioning (MC) using a rotor-stator high-shear device operated at a critical rotation speed. As a result, in-situ control of solidification behaviour is achieved to precisely tailor the as-cast microstructure. The billet grain refinement is attained by MC-DC casting without the deliberate addition of chemical grain refiners. The microstructure of the MC-DC cast billet at the critical rotation speed showed a fine-scale dendritic structure with refined secondary dendrite arm spacing (SDAS). The solidification front proceeded with a shallow sump and a corresponding shorter solidification time, higher cooling rate, higher temperature gradient, and smooth solidification rate profile. The ideal fine-scale dendrites with low SDAS divided the remaining eutectic liquid into fine-scale and isolated liquid pockets, resulting in fine-scale, compact morphology, and uniform distribution of second phase particles in the as-cast microstructure. The MC-DC casting process showed the ability to increase the cast house production rate by increasing the casting speed without bleeding the billet. The present approach could be beneficial for eliminating or reducing the homogenisation practice and may also introduce significant flexibility in using recycled Al alloys in the industry.Engineering and Physical Sciences Research Council (EPSRC) of the UK and Constellium (UK) STEP Al prosperity partnership grant (EP/S036296/1)

Influence of reinforcing particle distribution on the casting characteristics of Al-SiCp composites

Engineering and Physical Sciences Research Council (EPSRC), UK, through the Towards Affordable, Close-Loop Recyclable Future Low Carbon Vehicle Structures (TARF-LCV) programme, Grant No. EP/I038616/1

High Shear Dispersion Technology prior to Twin Roll Casting for High Performance Magnesium/SiCp Metal Matrix Composite Strip Fabrication

SiC particulate (SiCp) reinforced AZ31 magnesium alloy composite strips were produced by a novel process. In the process, a high shear technique was utilised to disperse the reinforcing particles uniformly into the matrix alloy, and AZ31/5vol%SiCp slurry was solidified into thin strip by a horizontal twin roll caster. The experimental results showed that the AZ31/5vol%SiCp strip obtained with high shear treatment exhibited a significantly refined microstructure and uniform distribution of reinforcing SiC particles. High cooling rate in the TRC process was also considered to contribute to the grain refinement of the matrix alloy, together with the possible heterogeneous nucleation effect of the reinforcing particles. The mechanical properties of the high shear treated composites strips showed enhanced modulus, yield strength and ductility by hardness and tensile tests. The experimental results were discussed in terms of the microstructural features and the macroscopic reliability, where necessary, analytical and statistical analyses were conducted.EPSRC UK, Towards Affordable, Close-Loop Recyclable Future Low Carbon Vehicle Structures (TARF-LCV), Grant No. EP/I038616/1

Comparative analysis of structure and properties of Nb-B inoculated direct chill cast AA4032 alloy extruded from as-cast and homogenised conditions

Copyright © 2022 The Author(s). Al-Si wrought piston alloys can lack properties due to inefficient grain refining. A novel Al-Nb-B grain refiner was introduced some time ago, but has still not been assessed in industry for wrought alloys. This paper describes the first trial of Al-Ni-B addition and its impact on the full-scale manufacturing, structure, and properties of the AA4032 products extruded with and without billet homogenization. It is shown that Nb-B inoculation gives opportunities not only to have a refined as-cast structure but also a more homogenous distribution of the solute. In contrast, homogenization drives nucleation and coarsening of the Mg2Si phase that is retained during further extrusion and heat treatment also affecting the precipitation and properties. It was observed that non-homogenized specimens perform better during machining and tensile testing compared to homogenized specimens. The results are supported by electron microscopy investigations of microstructure formation during different steps in downstream processing.UK Engineering and Physical Science Research Council (EPSRC Grant: The Future Liquid Metal Engineering Research Hub, under grant number EP/N007638/1); Constellium

Tailor Blank Casting - Control of sheet width using an electromagnetic edge dam in aluminium twin roll casting

A significant fraction of all sheet aluminium is scrapped during manufacture because the supply chain is configured to produce long coils of strip with constant width while end products are formed from irregularly shaped non-tessellating blanks. In this paper, an opportunity to reduce this rate of scrap is explored. Electro-magnetic edge-dams have been used previously to contain the melt in twin-roll strip casting of aluminium but here, equipment has been designed to allow rapid movement of such an edge dam during casting. This is named ‘Tailor Blank Casting’. The equipment is described and the first experimental trials are presented, with one edge of the melt constrained by a moving electro-magnetic dam in order to achieve a controlled variation in sheet width. The trials demonstrated successful containment of the liquid prior to solidification, and a sheet with close to step changes in width was cast. From analysis of the results of these trials, the mechanisms of width change are proposed and the effect of the moving dam on product properties is studied. The paper concludes with a discussion about possible yield savings and the next steps for further development of the process.The authors wish to thank Prof Zhongyun Fan at BCAST, Brunel University for allowing for the use of their horizontal twin roll caster, Siemens Metals Technology for funding the experimental work, and Dr Sanjeev Das and Mr Stephen Cook for their help in setting up and carrying out the casting trials. The first two authors are supported by a Leadership Fellowship provided by the U.K. Engineering and Physical Sciences Research Council (EPSRC) reference EP/G007217/1.This is the final version. It was first published by Elsevier at http://www.sciencedirect.com/science/article/pii/S0924013615001375

Tailor Blank Casting - Control of sheet width using an electromagnetic edge dam in aluminium twin roll casting

A significant fraction of all sheet aluminium is scrapped during manufacture because the supply chain is configured to produce long coils of strip with constant width while end products are formed from irregularly shaped non-tessellating blanks. In this paper, an opportunity to reduce this rate of scrap is explored. Electro-magnetic edge-dams have been used previously to contain the melt in twin-roll strip casting of aluminium but here, equipment has been designed to allow rapid movement of such an edge dam during casting. This is named 'Tailor Blank Casting'. The equipment is described and the first experimental trials are presented, with one edge of the melt constrained by a moving electro-magnetic dam in order to achieve a controlled variation in sheet width. The trials demonstrated successful containment of the liquid prior to solidification, and a sheet with close to step changes in width was cast. From analysis of the results of these trials, the mechanisms of width change are proposed and the effect of the moving dam on product properties is studied. The paper concludes with a discussion about possible yield savings and the next steps for further development of the process

Thermomechanical Treatment of High-Shear Melt-Conditioned Twin-Roll Cast Strip of Recycled AA5754 Alloy

A continuous high-shear melt conditioning twin-roll casting process has been developed for production of recycled aluminum alloy strip with minimum casting defects. High-shear melt conditioning is applied to increase the impurities tolerance of recycled aluminum. The results of this study showed that solidification during twin-roll casting can be controlled by using intensive melt conditioning prior to casting, which can promote equiaxed growth with minimal defects and result in improved sheet quality. Melt-conditioned twin-roll cast (MC-TRC) AA5754 alloy exhibited fine equiaxed grains and homogenized matrix structure while centerline segregation was eliminated. As-cast melt-conditioned twin-roll cast AA5754 strips showed clear grain recrystallization after thermomechanical treatment at 430°C for 30 min, representing an improvement over conventional twin-roll casting. The MC-TRC strip showed 57.2% higher elongation and 4.1% higher ultimate tensile strength compared with the TRC strip after applying melt conditioning with thermomechanical treatment.Innovate U