Effect of reduction ratio of hot-extrusion on microstructures of superplastic Si(3)N(4)whisker/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 compo sites are obtained in only samples prepared with higher reduction ratios. I n order to reveal the mechanism of superplasticity influenced by the reduct ion ratio, the microstructures of the composites, prepared with various red uction ratios, after tensile-testing have been studied by transmission elec tron microscopy. High reduction ratios in the hot-extrusion produce fine gr ains with 1-2 mu m in diameter, and also bring about interfacial reaction b etween the matrix and Si(3)N(4)w crystals. It can be concluded that the hig h 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.