Superplastic behavior and cavitation in high-strain-rate superplastic Si3N4p/Al-Mg-Si composites

High-strain-rate superplastic behavior has been investigated for Si3N4p/Al-Mg-Si (6061) composites with a V-f = 20 and 30 pct, respectively, where V-f is the volume fraction of reinforcements. A maximum elongation was attained at a temperature close to the onset temperature for melting for both composites, The maximum elongation for the 30 vol pct composite was larger than that for the 20 vol pct composite. Development of cavities transverse to the tensile direction is responsible for the lower maximum elongation of the 20 vol pct composite. However, development of the transverse cavities was limited to the optimum superplastic temperature for the 30 vol pct composite. The differential scanning calorimetry (DSC) investigation showed that a sharp endothermic peak appeared for the 30 vol pct composite, indicating that sufficient partial melting occurs. It is, therefore, likely that the stress concentrations are sufficiently relaxed by a liquid phase and that the development of transverse cavities is limited for the 30 vol pct composite.