Abstract
The influence of interfacial strength between the carbon fibers and the aluminium matrix on the bending strength (tensile strength) of the carbon fiber reinforced aluminium alloys (CFRM: PAN based high modulus (CF, Vf=70%) fabricated by pressure infiltration method has been studied. The CFRM with a matrix of Al-7.8%Mg alloy (CF/Al-Mg) having a high bending strength of 1250 MPa and a low compressive strength of 600 MPa shows pull-out fibers on the fracture surface of a bending test specimen under SEM observation, as the CFRM with a matrix of Al-7.1%Si-0.36%Mg alloy (CF/Al-Si-Mg) having a low bending strength of 600 MPa and a high compressive strength of 1000 MPa exhibits a flat fracture surface and high resolution TEM identified Al4C3 precipitates on the interface.
The cracked surfaces of bending specimens with a notch parallel to the fibers were analyzed using Auger Electron Spectroscopy(AES). The depth profile of the content of Al, C, Mg and Si at the aluminium matrix side of the surface revealed that the fractured position near the interface is in the interior of the carbon fiber. The distance of the fractured position from the interface in the case of CF/Al-Mg is comparatively shorter than the case of the CF/Al-Si-Mg. This means the interfacial strength of the CF/Al-Mg is low.
For the CF/Al-Mg, bending stress continues to increase long after the first Acoustic Emission(AE) signal is obtained and fracture of the specimen occurs finally when the stress of the total fibers reached maximum. This shows that the crack initiating from the fractured fiber can not propagate easily through the fiber. Fracture of bending specimen of the CF/Al-Si-Mg occurs very soon after the first AE signal is obtained, thus showing that the crack propagate through the fibers very easily.
