Study of Grain Refinement in Al Alloy 2519 using Backscattering Orientation-Contrast Mode in the Scanning Electron Microscope
Abstract
The effects of variations in thermomechanical processing (TMP) parameters on grain refinement in 2519 A1-Cu alloy were studied. Refined grains enhance tensile ductility and are a prerequisite for superplastic response. The TMP variables were adjusted based on panicle stimulated nucleation (PSN) theory. Process modifications included increased 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 5KV resulted in increased intensities for atomic number and orientation contrast. Both grains and theta- phase (A12Cu) precipitates were revealed on the same micrograph at higher 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 theta-phase particle diameter (d sub crit) for PSN. The theta-phase particle distribution was shown to be an important factor for grain refinement via PSN.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1992
- Accession Number
- ADA260886
Entities
People
- Jeffrey R. Dunlap
Organizations
- Naval Postgraduate School