Abstract
The effects of Mg and Si additions into the matrix on the tensile, bending and compressive strengths of the carbon fiber reinforced aluminium alloys (CFRM: PAN based high modulus CF, Vf=70%) fabricated by a pressure infiltration method have been studied.
The main results obtained are as follows.
(1) Mg addition up to 10 mass% to the Al matrix increases the bending strength up to 1250 MPa at about 8%Mg, but decreases the compressive strength to 600 MPa. The FRM with the matrix of Al-7.8%Mg alloy having a high bending strength of 1250 MPa and a low compressive strength of 600 MPa shows pull-out of the fibers on the fracture surface by SEM observation. No precipitates are observed by high resolution TEM in the interface between the fibers and matrix.
(2) Si addition of about 3% to the Al-Mg matrix makes a significant decrease in bending strength to 900 MPa and a small decrease in compressive strength to 500 MPa.
(3) Si addition up to 12 mass% to Al matrix makes a small increase in bending strength to 600 MPa and a significant decrease in compressive strength to a level lower than 500 MPa.
(4) Mg addition of about 1% to the Al-Si alloy matrix makes a significant increase in compressive strength up to 1000 MPa at about 7%Si, without changing of the bending strength. The FRM with the matrix of Al-7.1%Si-0.36%Mg alloy having a low bending strength of 600 MPa and a high compressive strength of 1000 MPa exhibits flat fracture like shear mode for bending test. High resolution TEM work identifies the Al4C3 precipitates on the interface.
(5) Tensile strength and bending strength have a relationship based on our results using thin bending specimen. Therefore, we regarded the bending strength as the substitute of the tensile strength.
