High strength 7xxx series aluminum alloys (Al-Zn-Mg) are commonly utilized in the aerospace sector but are difficult to extrude into complex shapes. Nanoscale phases known as dispersoids can significantly influence both the extrudability and the final properties of the product. The precipitation of dispersoids can be controlled either by adapting the chemical composition or the homogenization heat treatment. To assess the effectiveness of such measures, reliable analysis and quantification of dispersoids is required, which is commonly performed by Transmission Electron Microscopy (TEM). However, TEM requires expensive instruments, experienced operators, and substantial experimental effort. Conversely, scanning electron microscopy (SEM) offers a more economic and faster alternative, but resolution is limited in backscattered electron (BSE) microscopy. The achievable resolution depends on the accelerating voltage, as the interaction volume of BSE is smaller at lower voltage. However, low-energy BSE microscopy using conventional detectors is challenging due to suboptimal signal-to-noise ratios.

This study aimed to quantify nanoscale Al3Zr-dispersoids in variants of AA7108A aluminum alloy with modified Zn and Mg contents and significantly reduced homogenization times. A novel BSE detector, Gatan OnPointTM, was employed at low acceleration voltages (≤5 kV). Significantly improved resolution was achieved compared to SEM at 20 kV using a standard four quadrant solid state BSE detector (4-Q). Obtained dispersoid size distributions showed excellent agreement with TEM measurements.

These findings provide a rapid means of quantifying nanoscale Al3Zr-dispersoids in aluminum alloys, eliminating the need for expensive and time-consuming TEM investigations. This approach allows for the swift assessment of various homogenization variants, facilitating quick analysis for further optimization and enhanced extrudability.