Study of grain refinement in Al alloy 2519 using backscatter orientation-contrast mode in the scanning electron microscope

Abstract

The effects of variations in thermomechanical processing (TMP) parameters on grain refinement in 2519 Al-Cu alloy were studies. Refined grains enhance tensile ductility and are a prerequisite for superplastic response. The TMP variables were adjusted based on particle stimulated nucleation (PSN) theory. Process modifications included increases initial overaging time and decreased subsequent warm rolling temperatures. Backscatter orientation-contrast (BSOC) techniques for the scanning electron microscope (SEM) were developed to achieve grain-orientation contrast. An accelerating voltage of SKV resulted in increased intensities for atomic number and orientation contrast. Both grains and 0-phase (Al(2)Cu) precipitates were revealed on the same micrograph at high resolutions than attainable in the optical microscope. Quantitative data from micrographs were obtained using image analysis methods. A method based on statistical considerations was developed to determine an approximate critical 0-phase particle diameter(d(crit)) for PSN. The 0-phase particle distribution was shown to be an important factor from grain refinement via PSN..