TEM analysis of aluminum alloys submitted to ECAP

N. G. S. ALMEIDA; C. G. FARIA; J. A. CRUZ JÚNIOR; BUBANI, F. C.; AGUILAR, M. T. P.; CETLIN, P. R.

Belo Horizonte

Congreso; IX Congresso de Microscopia dos Materiais; 2016

Sociedade Brasileira de Microscopia e Microanálise

The microstructure of annealed and severely deformed aluminum alloys (1060 and 6351) is analyzed by qualitative and semi-quantitative TEM. For TEM analysis, samples were machined down to 3 mm diameter rods and ground down to foils of 50 μm in thickness on wet 1200 grit silicon carbide paper. These foils were finally electropolished at low temperature (?30°C) until perforation occurred, using a Tenupol-5 machine set at a voltage of 18 V. The electrolyte consisted of 70% methanol and 30% nitric acid. The foils were examined in a FEI-Tecnai G2-20 transmission electron microscopy and a Philips CM200UT both operating at 200 kV. The microstructure of the annealed alloy was analyzed and used as a reference for comparison. The alloy in the plastic deformed condition was initially annealed, and then submitted to several Equal Channel Angular Pressing (ECAP) passes. Severe plastic deformation of Al alloys causes significant microstructural modifications and grain refinement. Dislocations tend to group and form sub grains and dislocation cells, which results in low free dislocation densities inside grains. As plastic deformation increases, sub grains tend to rotate in relation to their neighbors, leading to crystallographic orientationmisalignment. This phenomenon results in regions where grains have similar orientations, but with relatively small, measurable misfit angles, which are clearly seen in the plastic deformed sample. Electron diffraction techniques are used to estimate the rotation angle between neighboring grains, at suitable crystallographic orientations. A comparison of the microstructure of the alloys shows significant differences in grain size and dislocation structure. Evidence of the interaction between dislocations and precipitates, which was observed inside few grains, is also presented.