Soldering aluminium

[GreensandsParticipant @greensands]

Hi all – I need to carry out a largely cosmetic repair on an aluminium casting as a result of a being a little too hasty on the milling machine. Essentially it would a (small) gap filling exercise but before resulting to using Araldite or similiar I would like to explore the possibilities of a soft solder repair as it would be a good excuse to try a new (to me) technique. Has anyone had any experience of soldering alumimiun and able to offer some suitable suggestions, e.g source of alloy, soldering tools etc. required for the job?

[GreensandsParticipant @greensands]

[Grindstone CowboyParticipant @grindstonecowboy]

I have successfully used Lumiweld for repairing motorbike castings, so it might be OK for this. Bought a kit many years ago, but I'm assuming it is still available.

Rob

[JasonBModerator @jasonb]

Cup do a flux for use with standard soft solders on aluminium as well as a cored solder specifically for aluminium

[peter smith 5Participant @petersmith5]

Hi

Chronos do a kit inc wire brush to remove oxide. There was a company a few years ago that did the exhibition circuit selling a similar product which was excellent . If repairing a crack don’t forget to stop it with hole.

Pete

[J HancockParticipant @jhancock95746]

Technoweld is the 'go to' , expensive if it is a big hole but easy to use without requiring huge amounts of heat.

[Brian WoodParticipant @brianwood45127]

A Google search for aluminium welding gives plenty of choices for low temperature 'brazing' joints using bars made from zinc/aluminium alloy. Lots of videos showing how it is done too

I was sceptical and tried them on extruded square section aluminium with success, the repair on a casting should be even better. Scrubbing the joint area with a stainless steel wire brush is the key to a good joint

Brian

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Jason,

I have always used technoweld / lumiweld for soldering aluminium. I have just followed up your lead on Cupalloy. They certainly do a flux for aluminium. However the only solder that they sell for aluminium, says that it is only for pure aluminium and aluminium / copper alloys. Is there any solder that works for the type of alloys that we commonly use?

Regards,

Andrew.

[henrybParticipant @henryb]

I ordered some off ebay earlier. aluminium brazing solder it melts at 300 degrees. you don't need flux with them. i think they are johnson mathey ones. the seller is called ablemablecrafts.

[JasonBModerator @jasonb]

From what I can remember of Keith's posts on the subject any of the soft solders can be used with the Harris flux but the problem is postage costs. This is why they also do the cored one as that can be posted at normal rates. Hopefully Keith will see the post and comment.

6082 (HE30) that we commonly use does contain copper though in far smaller amounts than something like 2014

[Martin KyteParticipant @martinkyte99762]

Rivet or loctite a plug into the casting and remachine perhaps?

Or my all time favourite if it's a small defect, drill and tap a suitable size, add a grubscrew and stamp OIL underneath.

regards Martin

[SillyOldDufferModerator @sillyoldduffer]

I've successfully soft soldered copper wires to Aluminium following Neil's advice which is to splash the area with thick oil, scrape the oxide off under the oil with a screwdriver, and then solder as normal with a big electric iron. It's the oxide layer that makes Aluminium difficult to solder and it forms almost instantly in air. Soldering works provided the joint is made before the oil burns off and lets air in. You can't pussyfoot with a small iron or use a flame because the oil fails before the Aluminium gets hot enough. I used a 200W solder gun. No idea if it would do for a cosmetic repair.

Dave

[GreensandsParticipant @greensands]

A lot of very useful help and advice given here – Thanks for that. It would appear that my best options would be to use either the Lumiweld 5 rod + Wire Brush Kit or to try Alsol, the flux cored solder sold by Cup Alloys. I should have said that the cosmetic treatment involves filling a line gap from the inside of a concave shell casting typically 0.020" thick x 1" long which after soldering would be filed down to maintain the external profile.

[EmgeeParticipant @emgee]

Posted by Greensands on 06/09/2020 20:26:19:

A lot of very useful help and advice given here – Thanks for that. It would appear that my best options would be to use either the Lumiweld 5 rod + Wire Brush Kit or to try Alsol, the flux cored solder sold by Cup Alloys. I should have said that the cosmetic treatment involves filling a line gap from the inside of a concave shell casting typically 0.020" thick x 1" long which after soldering would be filed down to maintain the external profile.

Good luck if you do go the Lumiweld, Technoweld, GAZ or any other route that requires a flame to heat the job so the rod runs, with such a small thickness of parent metal take a lot of care or you are likely to end with a hole and a spoilt casting.
Advise you have a few dummy runs with some scrap of the same material to be repaired.

Emgee

picture of another make of rod + flux

Another product from UK Brand: Sif Product Model: RO553212

Edited By Emgee on 06/09/2020 21:00:22

Edited By Emgee on 06/09/2020 21:09:07

[GreensandsParticipant @greensands]

Given the fact that there is not a lot of parent material around the line gap perhaps the best option would be the CUP Alloys Type Alusol flux cored solder having a melting range of 178 to 287deg C, quite adequate for what I have in mind provided that it 'sticks' to the casting

[EmgeeParticipant @emgee]

Posted by Greensands on 06/09/2020 21:14:34:

Given the fact that there is not a lot of parent material around the line gap perhaps the best option would be the CUP Alloys Type Alusol flux cored solder having a melting range of 178 to 287deg C, quite adequate for what I have in mind provided that it 'sticks' to the casting

That sounds like the safest option, vee the crack if you are going to file down to the surrounding surface, hope it goes well for you.

Emgee

[Nigel (egi)Participant @nigelegi]

I've used durafix with some success, here I filled in a hole so that I could re-machine it.

But I've also had a few disasters, the trouble is durafix doesn't use a flux and it doesn't wick between parts.

Therefore, problem I found first hand was it doesn't flow into the joint and between surfaces. Hence I kept adding more heat and didn't realise that the pooling of the durafix rod was actually mixing with molten aluminium from my crankcase that I had carefully machined.

All I would say is practice on some off cuts of material first.

[Roderick JenkinsParticipant @roderickjenkins93242]

I used HTS2000 for this:

HTH,

Rod

[Former MemberParticipant @formermember32069]

[This posting has been removed]

[John Graham 7Participant @johngraham7]

Aluminium oxidizes very quickly making it hard to solder. Coat the surface with sewing machine oil. Scratch the surface through the oil with a wire brush or the blade of a screwdriver. Don't remove the oil as it prevents oxide forming. Coat the surface with soft solder through the oil. You need a lot of heat because aluminium is an excellent conductor of heat and cools very quickly.

If you do aluminium brazing rub the surface of the aluminium with a brass bristle wire brush. This will remove the oxide and leave a light coating of brass on the aluminium which prevents further oxidization and helps the aluminium filler rod to stick.

John

[Former MemberParticipant @formermember32069]

[This posting has been removed]

[Danny M2ZParticipant @dannym2z]

Lumiweld works well if one carefully follows the instructions.

My first attempt restored a broken out mounting lug on an ancient DC Dart model diesel engine,

Apart from the fact thet the repair is a bit darker than the original it's still working quite well 20 years later

[Anthony KnightsParticipant @anthonyknights16741]

I found this in my drawer of soldering stuff. I've had it for a few years and haven't tried it lately, so I don't know if it still works. I haven't checked the RS site to see if they still sell it.

[Grindstone CowboyParticipant @grindstonecowboy]

Just seen an advert for this aluminium solder/low temp welding rods. No experience of it, but it's another possible source for anyone searching for some.

Rob

[David NobleParticipant @davidnoble71990]

Posted by Martin Kyte on 06/09/2020 18:35:11:

Rivet or loctite a plug into the casting and remachine perhaps?

Or my all time favourite if it's a small defect, drill and tap a suitable size, add a grubscrew and stamp OIL underneath.

regards Martin

Brilliant I'll remember that.

David

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