As the purity increases, aluminum becomes softer and is prone to mechanical deformation and scratches. Therefore, grinding may exacerbate the deformation of high-purity aluminum. So relatively speaking, the preparation of metallographic specimens of pure aluminum is more difficult than that of aluminum alloys.

Pure aluminum sample, etchant Barker reagent, 30V, 2 minutes. Observing with a polarizer, adding a sensitive color plate, with a magnification of 50X, the black spots are non-metallic inclusions.

It is recommended to use finer sandpaper for flat grinding to avoid excessive mechanical deformation. Hardness, size, and number of samples must be considered, but for rough grinding, even for larger pure aluminum samples, P600 sandpaper is sufficient, and larger aluminum alloy castings can be ground with P320 sandpaper. It is also important to have low pressure during grinding to avoid deep deformation and reduce the friction between the sandpaper and the sample surface, especially for pure aluminum.

Subsequently, all deep scratches generated by grinding must be removed using diamond polishing fluid. If the water solubility of the sample is unclear, it is recommended to use anhydrous diamond suspension and lubricant for polishing. If diamond particles are pressed into the surface of the sample during the polishing process, the polishing time of the subsequent silica suspension can be appropriately extended. It should be pointed out that embedded particles may lead to errors in organizational analysis.

After polishing with silica suspension for 1 minute, examine the results under a microscope. If necessary, polishing should continue for 1 minute and then recheck the results. It is recommended to repeat this polishing/inspection cycle until the required quality results are achieved. Approximately 30 seconds before the polishing is completed, pour water onto the polishing cloth to rinse the sample and polishing cloth. Then, wash the sample again with clean tap water and dry it.