Comparative quantification and statistical analysis of η′ and η precipitates in aluminum alloy AA7075-T651 by TEM and AFM

• Nanometric MgZn2 precipitates in AA7075-T651 were characterized using AFM and TEM.
• Phase-contrast AFM was used to differentiate metal matrix from MgZn2 precipitates.
• TEM and AFM micrographs were analyzed using commercially available software.
• AFM image analysis and TEM 2-D stereology render statistically equivalent results.

Quantification of nanometric precipitates in metallic alloys has been traditionally performed using transmission electron microscopy, which is nominally a low throughput technique. This work presents a comparative study of quantification of η′ and η precipitates in aluminum alloy AA7075-T651 using transmission electron microscopy (TEM) and non-contact atomic force microscopy (AFM). AFM quantification was compared with 2-D stereological results reported elsewhere. Also, a method was developed, using specialized software, to characterize nanometric size precipitates observed in dark-field TEM micrographs. Statistical analysis of the quantification results from both measurement techniques supports the use of AFM for precipitate characterization. Once the precipitate stoichiometry has been determined by appropriate analytical techniques like TEM, as it is the case for η′ and η in AA7075-T651, the relative ease with which specimens are prepared for AFM analysis could be advantageous in product and process development, and quality control, where a large number of samples are expected for analysis on a regular basis.