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2 Journal of Achievements in Materials and Manufacturing Engineering

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Processing and properties of AA7075/ porous SiO2-MgO-Al2-O3- composite

Robert M. H., Jorge A. F.

Journal of Achievements in Materials and Manufacturing Engineering

2012

Vol. 54, nr 1

7--15

Purpose: the work presents a new composite based in Al matrix reinforced with porous, lightweight and low cost SiO2-/MgO/Al2-O3- ceramic particles. The new material can present a unique combination of properties: those related to metal/ceramic composites and still associating some characteristics of cellular materials, as the low density and high plastic deformation under compression stresses. Design/methodology/approach: processing technique involves the infiltration of AA7075 alloy in the semisolid thixotropic state into a layer of porous ceramic particles. Products were analyzed by X-ray tomography, optical and electronic microscopy to observe microstructure and metal/ceramic interfaces. Density was measured by He picnometry; semi-static compression tests were performed to evaluate the deformation ability of the material. Thermal properties were theoretically evaluated. Findings: concerning the production method, thixoinfiltration is a feasible processing route, with no difficult control of parameters and does not rely on specific and onerous equipment. Moreover, it is flexible to different alloys. Concerning the product, low density composites can be produced with good dispersion of reinforcement and reliable internal quality; this material presents a plateau of plastic deformation at low stresses under compression, signalizing a potential application as energy absorbers. Theoretical simulations show also good thermal insulation ability. Research limitations/implications: as a new product, the full characterization of properties of the new composite is still to be achieved. Therefore, the full potential of commercial application is to be determined. The product can present limitations for application involving tensile stresses due to poor metal/ceramic interfaces. Practical implications: the thixoinfiltration can represent an alternative, low cost processing route for low density composites. The new composites presented are low weight and low cost material, presenting a unique combination of properties which can bring a whole new application field, as low cost, low density components for energy absorption and thermal insulation. Originality/value: both the processing route and the material produced - a low density metal/ceramic composite, using porous ceramic particulates as reinforcement, are new concepts under development by the proposing group at FEM/UNICAMP.

Thixoinfiltration: a new approach to produce cellular and other low density metallic materials

Robert M. H., Jorge A. F., Gatamorta F., Silva R. R.

Journal of Achievements in Materials and Manufacturing Engineering

2010

Vol. 40, nr 2

180-187

Purpose: the work presents an innovative approach for the production of cellular metallic materials as well as low density metal matrix composites, by using thixoforming techniques; thixotropic semisolid metal is infiltrated into removable and non-removable space holder preforms. Different kinds of preforms are tested to obtain open cell material (sponges), syntactic foams and low density composites. Products are evaluated concerning relative density and mechanical behavior under compressive stresses. Design/methodology/approach: Al alloy AA2011 was infiltrated in the semisolid state into preforms of sintered NaCl particles, sintered glass spheres, vermicular ceramic particles and porous ceramic granulates. After solidification, preforms were either removed by leaching (NaCl) resulting in open cell cellular product, or not (all others), resulting in composites of low density. Tomography tests were used to observe internal quality, and semi-static and dynamic compression tests were performed to evaluate the deformation ability of the material. Findings: results show that thixoinfiltration is a simple and low cost technique to produce different types of low density, porous material. Open cell material as well as syntactic foams and low density composites can be produced with reliable internal quality and dispersion of cells and reinforcement. Composites containing porous reinforcements can present some mechanical characteristics of the conventional cellular metals. Research limitations/implications: as all new developments, the complete understanding of the influence of processing variables upon the final quality of the product, as well as its consistency, must be provided before the technology can be widely used commercially. Practical implications: the technique can represent an alternative, low cost processing route for the fabrication of sponges, foams and low density composites, which can avoid restrictions and operational difficulties of presently available manufacturing processes based in liquid manipulation or powder sintering methods. Originality/value: infiltration of appropriate preforms by thixotropic metallic alloys to produce low density composites and cellular material is a new technique under development by the proposing group at FEM/UNICAMP.