Effect of reduction ratio of hot-extrusion on microstructures of superplastic Si3N4whisker/Al-Mg-Si alloy composites studied by transmission electron microscopy

It is well known that the superplastic behaviour of Si(3)N(4)whisker(Si(3)N(4)w) / Al-Mg-Si alloy composites is sensitive to a reduction ratio of hot-extrusion in the sample preparation, and that high elongations of the composites are obtained in only samples prepared with higher reduction ratios. In order to reveal the mechanism of superplasticity influenced by the reduction ratio, the microstructures of the composites, prepared with various reduction ratios, after tensile-testing have been studied by transmission electron microscopy. High reduction ratios in the hot-extrusion produce fine grains with 1-2 mu m in diameter, and also bring about interfacial reaction between the matrix and Si(3)N(4)w crystals. It can be concluded that the high superplasticity of the Si(3)N(4)w/Al-Mg-Si alloy composites results from the morphology with both the fine grains and the interfacial reaction.