skin stress considerations need to be made. Anodizing and surface contamination might result in some unexpected outcomes. shot peening does not remove contamination, it embeds it!
I suppose I should elaborate on my anodizing process and why nothing more than a degreasing is enough to make an excellent coating. With typical anodizing, the oxide layer grows, but is nonconductive so no current can flow. They typically fix that with various acids and harsh chemicals that etch into the coating, leaving pores that allow oxidation to continue. A sealer has to be used to close up the pores, though the pores offer a spot for dye to sit if coloring is desired.
In my process I deal with the insulative properties of the coating by using more voltage. The high voltage forces the oxygen atoms further into the aluminum surface. My best estimates give about a nanometer per volt, and I coated one test piece with 2000V (current limited) and left a very good hard anodize layer with no pores. I am essentially making a high voltage electrolytic capacitor.
A pleasant side effect is that no surface impurities have a dielectric strength near as high as the formed coating, so it all gets broken down, oxidized, or ignored in the process. An exception to that is iron impurities and likely other metals inhibit the process entirely by turning into a water soluble coating that never builds up. For example, a bit of laser slat melted into an aluminum part will sink all of the available current and prevent any anodization of the aluminum from occuring. To deal with this, I use a low voltage (30V) high current power supply to erode away impurities that affect the process in a matter of seconds to minutes.
To start with I can put over an amp per square inch and get uniform coatings. At higher voltages, as the power level increases microarcing occurs on the surface leaving a rough, porous surface. In the future I want to try making a thinner (say, 1um) nonporous coat then ramping the power up to make the remaining micron of the coating porous to accept dye and sealer, thus providing both exceptional corrosion resistance and color.
Another cool thing about the process is that although the parts of the component closest to the electrode start off coating fastest, they quickly become less conductive so the harder to reach areas such as tapped holes and inside corners also get a good uniform anodizing.
On the topic of shot blasting, I am almost entirely interested in removing machining marks with little time, labor, or dust. Cleaning is not a major concern.
I did just learn about spherical stainless powder, which is essentially stainless shot down to 15 microns, so that certainly opens up some opportunities (for disaster)
