During the polishing and etching of specimens of aluminum by conventional methods by solution (water + HF) for the microstructure, the powder may not homogenize with the base metal (aluminum) at elevated/ low temperatures in FSP thus, This powder leaves a void in its place.
so, What is the best way to polish and etch samples in friction stir processing with additive powder?
When using friction stir processing (FSP) with additive powder, it is important to take care during the polishing and etching of the samples to ensure that the microstructure is accurately revealed without leaving voids.
One approach is to use a polishing method that is specifically designed for FSP samples with additive powder. One such method is the use of diamond suspensions, which can effectively polish FSP samples without leaving voids. The diamond suspension is applied to a polishing cloth, and the sample is polished using a rotary polisher until the desired surface finish is achieved.
After polishing, the sample can be etched using a suitable etchant. The choice of etchant will depend on the specific material and the type of additive powder used in the FSP process. For example, if the additive powder is a ceramic material, a suitable etchant may be a mixture of hydrofluoric and nitric acids.
It is important to note that when etching FSP samples with additive powder, the etchant may react differently with the additive powder compared to the base metal. This can result in uneven etching and the formation of voids. To minimize this, it is important to carefully control the etching time and temperature and to use an etchant that is optimized for the specific material and additive powder combination.
Overall, the key to successfully polishing and etching FSP samples with additive powder is to use a method that is specifically designed for this purpose and to carefully control the process parameters to ensure accurate microstructural characterization.
It depends on Al alloys. However, it's better to observe the sample surface after polishing and etching to investigate the distribution of the additive particles. ASTM E407 can be useful to find the enchant for various Al alloys.
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