The potential of the scanning low energy electron microscopy for the examination of aluminum based alloys and composites

When studying the physical properties and technological parameters of aluminum-based alloys and composites, some partial tasks, connected with the microstructure of the material bulk, pose a problem for established microscopic techniques. The topography and distribution of submicrometer sized precipitates and of segregations on the particle/matrix interface, for example, are difficult to observe by conventional methods of transmission and scanning electron microscopy. The introduction of a high-resolution low-energy mode into the scanning electron microscope, relying on the deceleration of an already formed and focused primary beam just in front of the specimen, enables one to browse over the full electron energy range with great ease. This method offers added value consisting of the diminished interaction volume of electrons, the favorable combination of secondary and backscattered electron signals emitted at increased yields and collected at extremely high efficiency and the availability of unconventional contrasts excited by slow electrons. Demonstration experiments have been performed on structures based on the Al-Mg-Si alloy, and oriented towards examination of the Mg-Si precipitates in the alloy and sub-micrometer spinel crystals growing on the matrix-ceramic interface in a composite filled with alumina particles.