Study on high strain rate superplasticity of A 6061Al alloy composite reinforced with 30 Vol.% AlN particulate

An investigation on the superplastic behavior of 30 vol.% AlNp/6061Al composite prepared by powder metallurgy (PM) techniques was carried out. Superplastic tensile tests of the composite were performed at strain rates ranging from 10° to 10⁻³ s⁻¹ and at temperatures from 823 to 893 K. A fine-grained structure prior to superplastic testing was obtained by hot rolling after extrusion. The highest total elongation to failure of 438% was achieved at a temperature of 863 K and at an initial strain rate of 1.67×10⁻¹ s⁻¹ and the highest value of the strain rate sensitivity index (m) was 0.42 for the composite. Differential thermal analysis (DTA) was used to investigate the possibility of any partial melting in the vicinity of optimum superplastic temperatures. The formation of a liquid phase is attributed to the melting of the Al-Si eutectic phase at the surface of the AlN particulates at elevated temperatures, as determined by electron probe microanalysis (EPMA). The influence of the microstructure and the fracture behavior on the superplastic behavior of the composite was studied by transmission electronic microscopy (TEM) and scanning electron microscopy (SEM). A large number of matrix filaments were present at the fracture surfaces of the specimens when superplastic deformation of the composite was performed under the optimum superplastic test conditions. The presence of dislocations and fine recrystallized grains in the test specimens suggested that they play an important role in the high-strain-rate superplasticity for this composite.