Bead blasting aluminum for a work hardening effect?

rons · Aug 23, 2021

I have read about this for steel. What about for aluminum? Does it depend on the type of aluminum?

Using sand or Ballotini impact beads. Will the surface disruption cause it to become better for a white glove test.
So I'm getting lazy and don't want to paint the world. Just want some peace and quiet and a nice brushed/matt/(anything)
type of finish on Al.

fciron · Aug 23, 2021

Sand or glass bead finish traps and shows every bit of dirt.

Shot blasting for surface hardening uses much larger steel shot which is thrown mechanically at the parts as they roll in a sort of tumbler.

steve-l · Aug 23, 2021

It does not work on aluminum.

rons · Aug 23, 2021

The atomic level, with steel there is carbon and iron and other impurities.

With aluminum?

Dave G. · Aug 23, 2021

Shot blasting won't improve the fatigue properties because there in no endurance limit for aluminum alloys. For steel, if you keep the load below a limit, the part will in theory last an infinite number of cycles. Aluminum does not have that same property, no matter how little the load - the counter keeps ticking and the part will eventually fail.

Some of the aluminum alloys - the 5000 series - work harden and shot peening might be beneficial if you could do it without contaminating the surface with iron. The 2000, 6000, and 7000 series are all precipitation hardening and would not benefit from spot peening.

SAG 180 · Aug 23, 2021

Bead blasted aluminium seems to have surface tension as it will close on an end mill cutting a groove in bead blasted cast aluminium. You'd expect an aluminium casting to have zero internal stresses in it, we give it a coat of a rattle can clear frosted lacquer after blasting and a good clean with solvent.

boslab · Aug 24, 2021

Basting won’t really effect the internal structure, precipitation hardening will, aka age hardening it will change the surface structure, maybe smoothing stress raisers out but it not an accepted treatment to increase UTS to my knowledge, but like all things advances in materials processing who knows what the future will deliver, perhaps someone will find an alloy that does harden by impact?, it would be useful to say the least, mostly it ends up in an oven for 8 or 10 hrs to age harden, even though the high copper alloys can and do harden themselves at room temperature
Mark

dian · Aug 24, 2021

steve-l said:
It does not work on aluminum.

why do you say that? any (almost) metal will strain harden. the question is how much and if glas beads will do it. no? aluminum is frequently bead blasted, but mostly for appearance.

btw, series 3/4/5000 gain their strenghth from cold work (up to 300%) but their work hardening potential is almost exhausted as delivered, unless in the soft state for forming operations.

but no idea it op is looking for surface hardening or wants to avoid painting.

rons · Aug 24, 2021

dian said:
op is looking for surface hardening or wants to avoid painting.

The op can easily paint. Wants a surface that can be touched that doesn't rub off with a finger.

MaxPrairie · Aug 25, 2021

For matt finishes we blast with baking soda then anodize.

rons · Aug 25, 2021

Part of the issue is matching scrap pieces to a project.

You get one piece that was a portion of jig plate with a Blanchard ground surface.
Then another piece that has a straight brushed finish.

So the two pieces don't match already. Then every time they get wiped down there will be scratch marks. Unless the wipes are at all times parallel to the edges :nutter:

The Ballotini bead route way makes me regret getting rid of the blast cabinet. Might have to use a empty plastic trash container with a plastic bag and respirator.

rogertoolmaker · Aug 25, 2021

rons said:
I have read about this for steel. What about for aluminum? Does it depend on the type of aluminum?

Using sand or Ballotini impact beads. Will the surface disruption cause it to become better for a white glove test.
So I'm getting lazy and don't want to paint the world. Just want some peace and quiet and a nice brushed/matt/(anything)
type of finish on Al.

If your just after a clean Matt finish on Aluminum; Alkali Etch the parts. Degrease and Dip in a 50-50 solution of Sodium Hydroxide(lye) and Sodium Carbonate(Washing Powder). Operating temperature 140F degrees. Bead Blasting on Aluminum???

Roger

rons · Aug 25, 2021

rogertoolmaker said:
If your just after a clean Matt finish on Aluminum; Alkali Etch the parts. Degrease and Dip in a 50-50 solution of Sodium Hydroxide(lye) and Sodium Carbonate(Washing Powder). Operating temperature 140F degrees. Bead Blasting on Aluminum???

Roger

Does "Dip" mean for quick in and out? What color is the final product?

I just did a Ballotini bead blast 1/2 hour ago. And now rubbing a finger on the surface does not pick up a gray smear.
The surface is rough but uniform. I wouldn't doubt that some byproduct of the media is in the aluminum surface.
If I wasn't so against rattle can clear then that is what I would do.

rons · Aug 27, 2021

What I observe is a mat finish, of course. The first few wipes with some Simple Green and a towel picked up gray residue.
Now it's pretty clean and I suspect the blasting of media toughened up the surface, Proof is in the cloth and finger tip.

I am posting a picture of these two aluminum plates and a "item" swivel (made in Germany). I did not touch the finish on
the swivel. It is either powder coat or paint. I am not curious to find out.

Another factor is that I had the pressure at max and that media was really doing it's thing.
A side benefit is that finish is close to the swivel.

Scottl · Aug 27, 2021

If you are trying to harden the surface hard coat anodizing would be best.

rogertoolmaker · Aug 28, 2021

Dip about 30 seconds, depending on the condition of the surface. If left in the bath to long the parts will erode from the chemical action. It will leave a clean matt finish. Dip or flush the parts in water to remove the traces of the solution otherwise the parts will have streaks. May help to blow off with air.
Roger

newtonsapple · Aug 28, 2021

rons said:
I have read about this for steel. What about for aluminum? Does it depend on the type of aluminum?

Using sand or Ballotini impact beads. Will the surface disruption cause it to become better for a white glove test.
So I'm getting lazy and don't want to paint the world. Just want some peace and quiet and a nice brushed/matt/(anything)
type of finish on Al.

Shot peening is regularly used to improve fatigue properties of Aluminum components. The shot used needs to provide a hammering effect and not a cutting one. I believe cut wire shot that has been processes to have rounded edges is frequently used.

Now if you just want to finish the aluminum surface, get it anodized or chromate conversion processed. You can DIY chromate conversion using Alodine: Amazon.com: Henkel - Alodine 1201 Light Metals Conversion Coating/Bonderite M-CR, Gallon : Automotive

rons · Aug 29, 2021

The two flat plates after just bead blasting and cleaning are not too bad. The surface doesn't smear or wear away.
Always do like those finishes on refrigerator doors for no hand prints. But I am going to get some of that Bonderite.
Kind of nice to just pull out a gallon and do a simple plate, without having multiple tanks and exhaust fans.

Bead blasting aluminum for a work hardening effect?

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