I need to make some post caps out of .100" 3003-H14 aluminum. There are outside corner joints that need to be welded (GTAW). I have been shearing my blanks, and the sheared edge is nice and clean for welding, but I am considering getting my blanks cut at a laser cutter. Would the edges be ready to weld with no further prep (other than the usual solvent/brush), or should I just stick to the shear? I've attached a couple pics of the blanks and the finished caps.
Personally, I have welded alum that was water jet cut but none with laser. Had no problem with normal cleaning. The water is not just pure water but the additives did not bother the edge, enough, to cause an issue for welding.
Laser should be even cleaner in my opinion but I am anxious to hear what some of our alum experts have to say.
He Is In Control, Have a Great Day, Brent
Unless there is an accuracy problem with the shear cuts creating excess "hand fitting" labor time then which ever is cheaper.
If your time is better spent on other tasks besides shearing, then the laser vendor might be the way to go.
Since aluminum oxide is formed instantly (for all practical purposes of discussion) this "skin" removal will be required regardless whether the parts are sawn, shorn, or laser cut.
John hit the nail on the head.
Aluminum, regardless of the method used to prepare it must be cleaned just before welding. Sheared edges contain multiple tears and edges that oxidize upon exposure to air. Plasma cut surfaces using shop air also have oxidized surfaces. Waterjet and laser cut surfaces are exposed to air, so they too have oxides that must be removed prior to welding.
I read somewhere that 90% of the maximum oxide layer forms within 24-hours after being exposed to air. I take that to mean 45% of the maximum layer is formed within 12-hours, 22% within 6-hours, etc. That is probably an over simplification. I'm sure the reaction is inversely proportional to time, thus the oxide thickness increase is not as rapid as time passes. Simply said, the oxidation is most rapid upon initial exposure.
My practice is to limit precleaning to one shift, that is the welding must be completed within 8-hours. Still, all joints must be wire brushed immediately prior to welding and between each pass. Cut edges that form the groove face are cleaned by draw filing before fit-up. I use a Ferrier’s file if a Vixen file isn't available.
A word about wire brushing; hand brushing is the preferable to power brushing. Power brushing tends to burnish the aluminum surface, not good if you are trying to weld. when hand brushing, push on the forward stroke just like you would when using a hacksaw.
Happy New Year - Al
I preclean with acetone and follow that with 90% isopropyl alcohol.
The acetone leaves a residue. Isopropyl alcohol leaves the surface clean.
Best regards - Al
While I can't give specifics for aluminum you are right in that oxidze layer growth is inversely proportional to thickness. Used to have access to detailed studies on oxide layer growth for corrosion mechanics and prediction. Basically if you think about it, as the oxide layer gets thicker, its harder for an oxygen molecule to impact directly with an aluminum atom. Solid state oxidation therefore has some real time associated with it.
I suppose it's splitting hairs but my understanding was that aluminum oxide in open air formed in the microsecond time frame, and the only time you will ever have pure metallic aluminum is in an inert atmosphere or vacuum. Oxide growth does take some time to achieve maximum but it's always there on any human time scale.
We have a laser, and occasionally cut aluminum, but we rarely weld it for service components. If it was a fillet joint I would treat it as any other component, clean surfaces with correct degreaser and go. If was a butt joint, especially a small one or autogenous weld it may be worth while to clean the material. unlike waterjet, or shears, a laser cutter is a thermal process and leaves a ~0.030" deep "recast layer" of oxidized and hardened material, for metals that are sensitive to oxidation like titanium it is absolutely imperative to remove the recast layer prior to welding. For aluminum, it's probably a toss up depending on a number of factors.
We generally don't do any special cleaning outside of degrease, if I was doing lots of butt welds I would definitely hit the surface with a grinding wheel to get down to bright metal.
Good luck!
I built tool boxes for oil field semis in 2008. The aluminum pieces were laser cut at another shop. Zero problems encountered. They welded fine with GTAW.
Griff
A couple of points to remember when welding aluminum alloys, the oxide has about the same density as the unoxidized base metal. As such, the aluminum oxides do not float to the surface. The melting temperature of the aluminum oxide is several times higher than the aluminum, so the oxide remains as a solid in the weld pool. Aluminum melts at about 1220 degrees F, whereas the oxide melts between 3200 to 3600 degrees F.
The oxides do not melt and decompose in the weld pool, the oxides do not float in the weld pool, thus the weld can be adversely affected. the resulting weld can look perfect, but it can be rather brittle. I have taken bend samples that looked perfect visually, but snapped then in half with a small amount of flexing. The fractured surfaces showed little ductility and resembled shattered glass.
One never knows how the aluminum will respond unless the welding procedure is tested to demonstrate the mechanical properties. Hence, there are no prequalified WPS per AWS D1.2.
Happy New Year - Al
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