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2 2023

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Effect of pressing pressure on microstructure and selected strength properties of AlSi-CF composite castings

Zyska Andrzej

Composites Theory and Practice

2023

R. 23, nr 4

197--201

The results of the study of the microstructure and selected strength properties (Rm, E) of an aluminum composite reinforced with chopped carbon fibers are presented. Composite castings were produced by the combined method of mechanical mixing and direct squeeze casting. Silumin EN 44300 and carbon fibers with a diameter of 6-7 μm and a length of 5-6 mm with a metallic coating - Ni (Tenax) and without a coating (Fortafil) were selected for the investigations. Experiments were carried out for 4 pressure values in the range of 20-80 MPa and their impact on the structural homogeneity of the composites as well as the strength and elasticity of the castings was assessed. The beneficial effect of the metallic coating manifests itself directly in the properties of the composites. The tensile strength of the composites reinforced with Tenax fibers is approx. 250 MPa and is 10% higher than the Rm of the reference alloy of the matrix. This level of strength is achieved by applying a pressing pressure of 60 MPa. The lack of a cohesive connection of the fibers with the matrix and a significant number of internal defects in the structure of the composite reinforced with Fortafil fiber cause a reduction in its strength both in relation to the composite with Tenax fibers and the reference alloy. As part of the strength tests, it was shown that chopped carbon fibers cause a significant increase in the elastic properties (E) of composites with an AlSi matrix, while the effect of the preparation of the surface of the reinforcing phase as well as the pressing pressure on this property are insignificant.

Manufacturing of Composite Castings by the Method of Fused Models Reinforced with Carbon Fibers Based on the Aluminum Matrix

Szymański Paweł

Archives of Foundry Engineering

2023

Vol. 23, iss. 3

118--123

The paper presents an attempt to produce aluminum matrix composites reinforced with short carbon fibers by precision casting in a chamber with a pressure lower than atmospheric pressure. The composite casting process was preceded by tests related to the preparation of the reinforcement. This is related to the specificity of the precision casting process, in which the mold for shaping the castings is fired at a temperature of 720°C before pouring. Before the mold burns, the reinforcement must be inside, while the carbon fiber decomposes in the atmosphere at 396°C. In the experiment, the reinforcement in the form was secured with flake graphite and quartz sand. The performed firing procedure turned out to be effective. The obtained composite castings were evaluated in terms of the degree of alloy saturation and the displacement of carbon fibers. As a result of the conducted tests, it was found that as a result of unfavorable arrangement of fibers in the CF preform, the flow of metal may be blocked and porosity may appear in the casting.