Fracture Mechanism of the Al-25Si-X Composite Fabricated via Spray Forming and Extrusion 1- Experimental Investigation

摘要

The fracture mechanisms operative in the hypereutectic Al-Si-X composites fabricated via spray forming and extrusion were investigated in an attempt to improve the mechanical properties of the composites. Two different types of Al-25Si-X composites were prepared by varying matrix composition and heat treatment conditions; the hard/brittle sample revealed 0.8 percent elongation with 420 MPa U.T.S and the soft/ductile one revealed 16 percentelongation with only 165 MPa U.T.S. The effect of the crystallographic factor of Si particles on the crack initiation in Ai-25Si-X composite was regarded not to he important. In the case of the hard/brittle sample, the cracks were observed to be initiated from Si particles at a relatively high tensile stress of about 420 MPa followed by sudden crack propagation through the composite. On the other hand, in the soft/ductile sample, the stress was also concentrated at the Si particles. However, cracks were not developed until the sample was deformed in about 7-9 percent elongation.