Accession Number : ADA260886


Title :   Study of Grain Refinement in Al Alloy 2519 using Backscattering Orientation-Contrast Mode in the Scanning Electron Microscope


Descriptive Note : Master's thesis


Corporate Author : NAVAL POSTGRADUATE SCHOOL MONTEREY CA


Personal Author(s) : Dunlap, Jeffrey R


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a260886.pdf


Report Date : Dec 1992


Pagination or Media Count : 57


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.


Descriptors :   *THERMOMECHANICS , *PARTICLE SIZE , *ALUMINUM ALLOYS , *BACKSCATTERING , *SCANNING ELECTRON MICROSCOPES , *GRAIN STRUCTURES(METALLURGY) , DIAMETERS , PARAMETERS , COPPER ALLOYS , ORIENTATION(DIRECTION) , VOLTAGE , ATOMIC PROPERTIES , DUCTILITY , IMAGES , PARTICLES , ELECTRONS , VARIATIONS , VARIABLES , PHASE , NUCLEATION , SUPERPLASTICITY , PRECIPITATES , ROLLING(METALLURGY) , THESES , INTENSITY , TENSILE PROPERTIES , MODIFICATION , TEMPERATURE , DISTRIBUTION , AGING(MATERIALS)


Subject Categories : Properties of Metals and Alloys
      Plastics
      Atomic and Molecular Physics and Spectroscopy
      Thermodynamics


Distribution Statement : APPROVED FOR PUBLIC RELEASE