Particle Size Distributions in a DC-Cast and Rolled AA3104 Alloy

Particle size distributions in an AA3104 alloy homogenized at different temperatures have been determined using both scanning electron microscope with a field emission electron gun (FEG-SEM) and transmission electron microscope (TEM). Constituent particles and dispersoids were measured at different depths for two hot rolled gauges. The measured area size distributions are transformed to 3D distributions using a modified Johnson-Saltykov method assuming different shapes of the particles and considering the information depth in the SEM and the TEM foil thickness. The analysis shows that the assumptions made regarding information depths have a large influence on the 3D size distributions and consequently also on calculated Zener drag. The very inhomogeneous particle distribution in the ingots makes it important to spread out the selected image fields to achieve reliable statistics also during the measurements on the hot bands. The TEM and FEG-SEM measurements give results in excellent agreement. Calculation of the Zener drag from the mean particle diameter and volume fraction gives values 4-5 times larger than those obtained using a more rigorous method considering the particle size distribution.