Selected properties of aluminium-silicon carbide composites obtained from powders by hot forging and cold working
Marek Wojtaszek, Stefan Szczepanik Akademia Górniczo-Hutnicza, Wydział Metalurgii i Inżynierii Materiałowej, al. Mickiewicza 30, 30-059 Kraków
Quarterly No. 3, 2005 pages 70-76
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abstract The work presents the results of research of materials obtained from powder using the technology that combined powder metallurgy and metal forming. Semi-finished products for the research were produced by forging the aluminium powder compacts and composite compacts containing 5 and 10 vol.% of silicon carbide particles at 500°C in closed-die. The obtained materials were cold-formed at room temperature with the reduction of height 8 or 25%. The volumetric content of the particles of SiC in the matrix and the influence of cold deformation on the relative density (Fig. 3), hardness (Fig. 4) and microstructure were investigated. Flow curves at room temperature and at elevated temperatures (Figs 5 and 6) were elaborated in order to analyse the behaviour of the materials during deformation. Basing on the realized research concerning hot forging of products obtained from aluminium powder and aluminium based composites reinforced with silicon carbide particles, it can be stated that the proposed forming technology makes it possible to obtain products showing high relative densities. It was found, that the addition of silicon carbide particles lowered the density of composite materials. Evaluation of the product microstructures qualitative confirmed density measurements results. Introducing the strengthening phase into aluminium matrix or cold forming leads to the increase of product hardness. During uniaxial compression test the change of temperature up to 150°C did not cause any significant drop in the stresses indispensable to obtain specified deformation, while at 200°C flow stress lowers significantly. In case of the aluminium matrix and composite with 5% silicon carbide volume fraction the flow stress increases, regardless of the test temperature and the amount of cold deformation after forging. Composite material with 10% silicon carbide volume fraction undergoes a failure under lower stresses and deformations when compared with aluminium matrix without silicon carbide particles. Key words: Al-SiC composites, powder metallurgy, hot forging, deformation, flow curves