Home Forums General Discussion Ask Dr. Peener Risk of Aluminum part contamination by steel shots

I work in an aerospace industry and out aluminum parts (7075-T6 alloy) are shot peened with stainless steel cut wire shots but they are peen formed with cast steel shots before anodizing. I would like to know if an alkaline cleaning and a very short deoxidizing (no material removal) are enough to eliminate the risk of lower corrosion resistance or any risk for the parts (mechanical properties, fatigue...)

Deoxidizing alone with no metal removal will normally not remove embedded cast steel shot peen residue. Some etching is usually required. However, most anodizing processes include some form of etching (metal removal) as part of the anodize process. This etching may or may not be sufficient depending on the amount of removal. A quick way to verify would be to make an aluminum shot peen sample utilizing your typical peening/forming process. Perform the etching normally required by the anodize process, complete the anodize process and subject the panel to typical anodize salt spray testing. If you have any residual iron on the surface, you will fail the salt fog test in short order. If you fail, you can go back and add additional etching prior to anodize. If you pass, then the etch associated with the anodizing was sufficient.

I recommend a nitric bath, similar to passivation, for shotpeened parts prior to anodize. Alkaline clean, nitric bath, alkaline clean, deox, anodize, with thorough rinsing in between. We use this for all of our aerospace aluminum parts that are shotpeened and anodized, regardless of media used or type of anodize.