Introduction: How to Solder Aluminum.

Up until recently I didn't know how easy it is to solder aluminum with a propane torch. The torch I'm using has a broad flame so it's probably not as efficient in heating the specific area for welding. A torch with more of a pin point would do better. In either case if you have a propane torch and brazing rods you can weld aluminum. All this can be found at your local hardware store. The rod cost about $3.00.

Step 1: Get the Right Rod.

In the same isle where all the stuff is for arc welding you'll find aluminum brazing rod. I got mine at Home Depot. It has a working temperature of 700 to 750 degrees Fahrenheit. A propane torch burns hot enough to get the job done.

Step 2: Clean Your Joint

Any time metal is being fused together it's always best that you clean it off. Long story short, clean metal sticks to clean metal. I'm using a wire brush on both surfaces. Now you're ready for some heat.

Step 3: Brazing Aluminum.

Apply the flame to the joint until it's hot enough to melt the rod. When you sweep the tip of the rod through the joint it should melt in. If not, heat the joint more and check it again with another sweep. You want the metal to melt the rod not the flame. When everything is cooled off you'll have a strong joint. Check out the last picture where I tried to pull the joint apart in a vise. The metal got all bent up before the joint failed.

Comments

author
G-baby (author)2015-04-02

Nicely done instructable. I do want to try this to make some 10" aluminum lawnmower blades for my electric mower.

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ac-dc (author)G-baby2015-05-17

Although you "could" do that, as Jissan mentioned it is too soft for the cutting edge so you would need to use stainless fasteners to bolt on hardened steel blade edges.

Considering this extra complexity, weight of fasteners, pain cleaning grass off to swap them, AND that steel blades made specifically for the purpose already exist, it would be a silly thing to do.

author
G-baby (author)ac-dc2017-02-10

ac-dc, you make a solid argument. It accrued to me to add a steal leading edge to the blades to aid in cutting. The steal blades would need to be thin and have holes to allow them to be mounted and replaced when they wear down. I still think there might be some performace gains from a lighter mower blade. Perhaps a composite of aluminum, kevlar, carbon fiber, and steal would create the ideal light weight but strong blade.

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noneYettookmyUN (author)G-baby2017-04-21

G-baby. I appreciate the need to tweek, alter and improve things. An aluminum mower blade is not an improvement for several reasons, only one of which is safety. The other two that spring to mind are efficiency and performance.

You mentioned that Al can be "more rigid". In the case of a mower blade that's actually a bad thing. A softer metal can absorb impacts (rocks, stumps,...), deform a bit, and carry on. A very hard metal may show less damage, but the internal fatigue builds with every impact. A soft blade will be dented, where a hard one will be chipped. Chipping is worse. The soft blade can be resharpened and used until there is almost nothing left. The hard blade will work until it fails. (And when it fails, Oh Boy!).

Regarding EFFICIENCY, it is as nophead said, the lighter blade will only save battery at spinup. Unlike a car going uphill, your blade is not fighting gravity, just grass. A lighter blade could conserve energy if you just start and stop your mower. If you mow with it, however, that's another story. Because then what consumes energy is not the mass of blade, but the blade of grass. :)

Which is where we come to "power", or PERFORMANCE. As has been mentioned, a lighter blade will not really affect efficiency. When it comes to performance, a light weight blade would likely be a negative. With the blade spinning free above the driveway, your motor probably approaches its no-load speed. This would be the same with a light blade, heavy blade, or no blade at all. What requires the motor to work is the initial spin-up, and then maintaining that speed when energy is lost to hitting (cutting) things. And what carries the motor's energy to the ground? The mass of the blade. While a light blade is easy to spin up, every impact will sap more of its stored energy, so the motor faces many sudden little load peaks to keep its speed. I.e. the motor will feel every blade of grass more. With the heavy blade, once it's going, it'll just go. It will only take an easy, steady push to keep speed, and the motor will be comfortably cushioned from all the work beneath. In fact, electrics often use a motor that is too weak to instantly produce all the force that might be needed, and instead rely on energy stored in a flywheel - in this case the blade. Light blade, light flywheel, less work. If you ever let your grass get too tall or thick I can assure you that, with a lighter blade, your mower would have more trouble hacking through it.

Here's something you should not try, to illustrate. Imagine a bicycle wheel, spinning on a stand. First, super-light Al wheel. No mass at all. If you stick your finger in the spokes, it'll stop so easily that you might not even learn your lesson. If you wanted to cut your fingers off with that wheel, you'd need someone who could pedal pretty hard to keep it going fast enough to do the work. On the other hand (because you still have another), look at a heavy steel wheel. Big rubber tire, maybe filled with rocks or lead. HEAVY! Once you have it spinning good and fast, you could stop pedaling and it'd still break your fingers 5 minutes from now. (Again, don't do this. Not with your lawn mower, either. :) )

Happy mowing!

author
BruceB49 (author)G-baby2016-04-14

Please don't! At its best, aluminum is prone to fatigue cracking; a brazed, soldered, or welded aluminum will fail very very quickly. This is asking for a large shard of aluminum embedded somewhere very painful.

author
G-baby (author)BruceB492017-02-10

That's a good point. I only wanted to do this because aluminum is so much lighter than steal. In theory, the aluminum blades(2) would require much less energy from the motors to turn. Thus, the blades might spin faster and/or the batteries would last longer per charge.

author
nophead (author)G-baby2017-03-31

Lighter blades would only take less power to initially spin up. Once spinning the mass makes no difference to the power needed to keep it spinning. That is down to air resistance, bearing friction and how easily it slices through the grass.

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taityw (author)G-baby2017-02-23

let me know if you die

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DougM2 (author)G-baby2015-05-17

G-baby - NO - aluminum will crack under the stress due to the constant vibration due to grass clippings, dirt and out of balance - the results could be fatal There is a "solid" reason why blades are made out of steel.

author
G-baby (author)DougM22017-02-10

DougM2,

I do think blade failure is a possibility. However, if great care is taken to balance the blades and there are no stress risers, the blade should hold up the the inertia of being spun.

author
Jissan (author)G-baby2015-05-17

Aluminum is soft and I don't think would be very good as lawn mower blades.

author
G-baby (author)Jissan2017-02-10

Yes, aluminum is softer than steal, but it is more ridged and much lighter. If the blade could be made with interchangeable steal inserts on the leading edges, there could be a benefit to having a set of blades that have much less mass to reduce the stress on the electric motors. This could create more efficiency or power.

author
DIYAnnaB (author)2016-04-09

Please forgive me for anything ridiculous I may say. I am renovating a vintage aluminum trailer and am sad to report that I had a little something done at a repair shop and they ended up shooting several brads through the skin of it! The holes are therefore small. I'm a middle aged woman and I do a lot of DIY home projects and construction but have yet to launch into welding. I wonder if it would be possible for me to use the product shown above and my soldering iron to repair these small holes and get it watertight again?

IMG_9099[1].JPG
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Mrballeng (author)DIYAnnaB2016-04-09

I don't think a soldering iron would get hot enough. And if you could get the area hot enough you might burn the materials near it. I would use "JB Weld" if I were you.

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JosephP36 (author)Mrballeng2017-01-01

It isn't the temperature alone. It's the Watts or Joules that are not high enough for large pieces. Your typical electronically controlled iron can be set for 850f and that's more than sufficient. But, for a large volume you might need 500W or more and most irons that can reach the required temperature are in the 100 to 150 Watt range. Sufficient for wire to wire or small tab to wire.

author
DIYAnnaB (author)Mrballeng2016-04-10

Thank you Mrballeng. I've used JB Weld with success on other things but only for joining metal things, not in places where the final finish of it would be important. Would JB Weld be able to polish up shiny like the surrounding aluminum? Or would I just be counting on it being a small enough spot so as not to be noticeable? That reminds me that I recently picked up a new (to me) JB Weld product at an auto parts store just because it looked interesting and potentially useful. It's called SteelStik (steel reinforced epoxy putty). I may do some research and see if this is an application where it would make sense. Thanks for the reminder! Also, do you know what would be the best product for cleaning the aluminum before attempting repairs? I've got old 1955 dirt.....putty tape.....and new auto grade caulk (applied by the same people who shot holes in the skin) all over this thing now. Something acidic? I don't want to ruin the shiny aluminum if I can help it.

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MartinB189 (author)DIYAnnaB2016-05-27

Some high quality irons will get this hot but Mrballeng is right a torch or JB Weld for wholes that small are a better idea.

author
jims72 (author)2016-11-29

I used a similar product called alumiweld from harbor freight too repair the action tube on a franchi 48 al 12gauge shotgun. It worked pretty good.

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Man Up (author)2016-09-04

You can increase the strength of your brazed joints by putting a bevel on the edges where they meet. The bevel should be half the joint, so if you have a butt joint (180 degree) then two 45 degree bevels. Don't cut the bevels all the way through - about half the thickness of the material should be good. This allows more filler material to penetrate the joint.

author
bo3ek (author)2016-05-25

HI

I used rods from http://alumsolder.co.uk and I joined two aluminium sticks for my project with no problem. The only thing to be focus on is the source of heat to be efficient to the size of aluminium parts. Weld is very strong and rods did the job.

author
DarrenO9 (author)2016-05-15

Making a rear ul aluminim bumper brasing.

author
Yonatan24 (author)2016-03-29

Hi, I've added your project to the "Beginners Guide to Soldering" Collection

This is the link If you are interested:

https://www.instructables.com/id/Beginners-Guide-to...

author
betwys1 (author)2015-05-18

As everyone is pitching in with methods, I take this opportunity to mention practical soldering - lead/tin soldering, that is, rather than brazing (brass rod), silver solder (4%-50% silver), bronze welding, MIG & TIG methods. Using lead/tin solder on favorable pieces is a way to win bar bets. Two small strips of aluminum sheet are prepared with a stainless brush. A propane torch is used to make a puddle of solder on the clean surface to be joined, of each piece. A pen-knife is used to scrape the surface UNDER the molten solder ball. You will see that it adheres where the oxide has been scraped off. Persist until a good patch of each strip has been tinned. Then sweat the tinned surfaces together. This is a tear-resistant joint which tends to break one of the strips first, away from the joint! Bingo!

author
HerbertD1 (author)betwys12015-09-04

I used your method to solder 10mm copper Tubing to an Aluminium plate(as a water cooling device for an Video card).

I used 3%Cu rest Sn( which is for copper brazing of water installation). I tried pure tin also but not so successful. The tinning of the alu plate was much much easier than the doing the copper tube, very astounding.

author
kentcampbell (author)2015-08-31

You you use this to fill an imperfection or casting defect in a piece before polishing it?

author
brian5003 (author)2014-09-12

As others have said, this is not welding. To weld aluminum you need a tig welder utilizing an inert gas to shield the arc. The problem with welding aluminum is that aluminum melts at 1200 degrees but aluminum oxide melts at 3700 degrees.

First a really clean piece of aluminum and even then there is a small amount of aluminum oxide. You need an ac arc to break thru the oxide layer to heat the aluminum and an inert gas to shield your welding to keep the oxide from reforming.

Good Luck.

author
SRQ Sid (author)brian50032014-09-14

Interesting post. Does anyone use gas welding for aluminum anymore? In the welding class of the Airframe & Powerplant Technician course I took many years ago I recall doing flat, vertical, and overhead aluminum welding using oxy-acetylene with excess acetylene.

author
bettina-sisr (author)SRQ Sid2015-05-23

THANK YOU! No one believes me when I say you can weld alum w/OA! HA, now I have proof lol :-)

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tkjtkj (author)SRQ Sid2015-05-17

I concur .. got my airframe and powerplant in Boston .. oxy-acet all the way ...

Chrome-moly? no prob ;)

author
Ilan Voyager (author)SRQ Sid2015-05-17

That works always on dirty (oil saturated for example) metals impossible to weld with TIG or MIG, as the flux fluorides are nasty but very effective for cleaning the alu. I have repaired a Honda gear box carter, after 4 attempts by other shops using MIG and TIG, with my good old aviation torch; the welding was a breeze with a fluoride flux and 4047 rods. The longest was to grind all the disaster left by the other shops. The welding was neat and none porosity.

author
ArcticNemo (author)SRQ Sid2014-09-15

Sid, I think I'm at the back end of that generation. My A&P semester final was an Al box done w/o fill, mostly to tweak the instructor who had decided I wasn't slick enough to make his fuel tanks or train on the only TIG unit. I also got the last session offered for doping, as the FAA dropped that. All 20 years ago.
Later I tried hydrogen, a world of difference for keeping work clean.

author
SRQ Sid (author)ArcticNemo2014-09-15

Hi Arctic... I guess I was a little ahead of you, like 33 years! I graduated from Embry-Riddle's Miami campus 10/61. My notes include rigging diagrams for Stearmans and J3 Cubs,tuition $70/month.

Regards, Sid

author
brian5003 (author)SRQ Sid2014-09-14

You could use oxy/acetylene, but you end up with a brittle weld with all the aluminum oxide. dont want to do that on a boat.

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SRQ Sid (author)brian50032014-09-14

The excess acetylene in a reducing flame produced an envelope to lessen oxidation. It was FAA approved. A brittle weld is not good for aircraft either.

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BigAndRed (author)brian50032014-09-14

Aluminum melts at 660 degrees C and is normally done with a MIG welder with Argon gas and aluminum filler wire, eg roo bars on 4WD and trucks. not really necessary to have a very clean surface. TIG is used on stainless steel.

author
al_packer (author)BigAndRed2014-09-14

In boat construction I've seen both MIG and TIG welding on aluminum. By and large, the TIG welds have tended to be more uniform and "better looking" when cosmetics are an issue, especially where you don't want to grind the weld bead. If I recall correctly, aluminum welds only achieve 60% of the strength of the surrounding metal, so a ground off bead is a potential failure point.

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brian5003 (author)BigAndRed2014-09-14

660 c is approx 1200 f

yes mig can be used, but ac tig can be used as well. I would argue that a clean surface is essential to a good weld but to each their own.

my point was that he was not welding.

tig is not exclusively for stainless

author
Technoaussie (author)brian50032014-09-14

Just to clear up the issue of using heat to join aluminum... As a retired specialist Aluminum boat builder I know a thing or two about the metal and how to join it. If you look at the stern (the blunt end) of an aluminum boat you'll notice the weld used is different to a weld that has extrusion of aluminum acting as the chine or edge of the boat. The stern is welded with a TIG welder -- The same as you use to weld stainless steel whilst the chine where a solid extrusion is used (mainly to absorb heat) is welded using a MIG welder.

Soldering aluminum has been around for decades. I remember first seeing it demonstrated 48 years ago at an agricultural show. The strength of a soldered joint depends on so many variables that you simply can't rely on it.

Today's techniques for advanced boat building is not to weld anything at all but to design a seam that can be glued using heat curable adhesive similar to that used in some aircraft construction. Finding an oven big enough to bake a boat and the jig that holds it until the adhesive is cured is the issue with this but the joint is measurable in strength and often exceeds any heat join because unlike welding or soldering, the adhesive does not alter the tensile strength of aluminum or create localized stress points.

There is a use for soldering aluminum. Having an instructable as well detailed as this one is certain to help someone who just needs to join aluminum without any stress considerations. I just felt the need to clearly explain the different ways of joining the metal with heat and without heat.

author
BigAndRed (author)brian50032014-09-14

i agree about solder v weld. Ive never 'soldered' ali.

we use metric here so I dont know about archaic systems of measurement like F ;-)

only used mig on ali and tig on ss when I was welding professionally. mig is cheaper and quicker when doing it all day as a job. only welding i do now is arc welding with 2mm thin sticks on steel tube.

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burnerjack01 (author)brian50032014-09-14

It should also be noted that for good results, an AC power source is required as during the reversed polarity phase of the arc the aluminum is being cleaned.

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Mrballeng (author)brian50032014-09-12

Your right. I mistook the definition.

solder ˈsädər/ noun

a low-melting alloy, especially one based on lead and tin or
(for higher temperatures) on brass or silver, used for joining less fusible
metals.


As opposed to....

weld1 weld/ verb

gerund or present participle:welding

join together (metal pieces or parts) by heating the surfaces to
the point of melting using a blowtorch, electric arc, or other means, and
uniting them by pressing, hammering, etc.

It's changed. Thanks!

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pfred2 (author)brian50032014-09-12

They make aluminum welding sticks. But be seated when you find out what they cost.

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IanM13 (author)2015-05-22

Great instructable! I've seen others where the surfaces being joined were roughed with hard scrubbing, and then 'wet' with a thin layer of solder, assembled, and then joined with more solder. The parts were slammed with a small sledge until they totally deformed, and the join never showed any sign of cracking.

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kpurse (author)2015-05-20

Good job dude

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garethllewelyn (author)2015-05-19

Super, clear and to the point, thanks.

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discostu956 (author)2015-01-19

what flux is appropriate for brazing aluminium?

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zacker (author)discostu9562015-05-18

I think the coating on the rod is the flux. it melts first then the wire melts and that's how it fluxes the joint to be welded.

author

No flux used, just needs to be clean, the demonstrators suggested a clean SS wire brush reserved just for the process.

author

imho, for what it's worth...check out Muggy Weld, for brazing aluminum

author
plantprof (author)richard.lozier2015-05-17

If a flux were used between the aluminum surfaces contacting each other, would the flux allow the aluminum rod to melt and flow into the joint instead of just making a bead along the edge? [As in soldering thin copper or tin plates together.]

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