Suggest a repair method for broken aluminium alloy casting

[AJAXParticipant @ajax]

Cracked motor foot

[AJAXParticipant @ajax]

Can anyone suggest a suitable method to repair this broken casting on a foot-mount motor? I would prefer something that looks good and strong (rather than JB Weld and some thick paint) but I would prefer not to invest too much time or money.

My stick welder is not suited to this job but I do have a good propane torch which I only use for heating parts up for assembly/disassembly. I have no experience using aluminium brazing rods. I realise there are cheap brazing rods available online but I'm guessing they are not particularly good.

I may end up pinning the joint, but I may need another look to see if this is possible. Pinning could also be combined with wrapping some flat around the corner and screwing it for reinforcement. However, I don't expect this would look very pretty.

I look forward to your suggestions.

[Brian WoodParticipant @brianwood45127]

I have made repairs with the aluminium brazing rods which are strong enough in that sort of thickness. They look satisfactory too

I recommend you try them. Be sure to use a stainless steel brush to abrade the joint all round before you apply heat, the brazing torch should be quite adequate, this is not high temperature work

Regards Brian

[AJAXParticipant @ajax]

Posted by Brian Wood on 01/05/2022 18:04:56:

I have made repairs with the aluminium brazing rods which are strong enough in that sort of thickness. They look satisfactory too

I recommend you try them. Be sure to use a stainless steel brush to abrade the joint all round before you apply heat, the brazing torch should be quite adequate, this is not high temperature work

Regards Brian

Thanks for your suggestion, Brian.

Do you think it would be a good idea to grind the crack out a bit before brazing? Vee-groove all round? I could do this quite easily with a rotary burr. As it stands, it would be impossible to clean the faces inside the crack without opening it up somehow. Do the brazing rods work well in filling cracks and if so what is the optimal gap?

[Pete RimmerParticipant @peterimmer30576]

I'd tig weld that for you if you were able to bring it to me in N Kent.

[AJAXParticipant @ajax]

Posted by Pete Rimmer on 01/05/2022 18:22:25:

I'd tig weld that for you if you were able to bring it to me in N Kent.

Pete, that's very kind of you to offer; however, I'm going to get some brazing rods and give it a try on some scrap. I'd like to see if I can do it myself as it could be a useful skill for future tasks.

[AJAXParticipant @ajax]

Posted by Brian Wood on 01/05/2022 18:04:56:

I have made repairs with the aluminium brazing rods which are strong enough in that sort of thickness. They look satisfactory too

I recommend you try them. Be sure to use a stainless steel brush to abrade the joint all round before you apply heat, the brazing torch should be quite adequate, this is not high temperature work

Regards Brian

Brian, what is the claimed melting temperature of the rods you used? Most seem to be 392 C with some more expensive ones that claim 300 C.

[Anonymous]

For similar jobs I use Benzomatic Aluminium solder rods. Unlike other makes you don't need to keep scratching the surfaces with a stainless brush, the flux stuff it's coated with lets it work without. Will be strong enough for your job, I've butt welded alloy tube to alloy plate with it and had to really whack it with a club hammer a couple of times to break it.

This is a thermostat housing off an old bike I repaired with it, just make sure the surfaces are really cleaned up first, I used a burr on it to get to bright metal on this.

[noel shelleyParticipant @noelshelley55608]

If your using the low temp rods and can weld FORGET ALL YOU KNOW ! Read the instructions and do JUST AS IT SAYS. I have used these rods with success on a high load job and was amazed that it held. There are numerous trade names, though for aluminium they are not made of that metal, I think it is a high Zinc alloy. You need to heat the whole casting, not just the broken area, and when it flows it will be a strange event, BUT IT WORKS ! Good Luck Noel.

[SteviegtrParticipant @steviegtr]

I too have used that method on a Renault alloy sump , that had hit a brick. It was a proper mess. But those rods worked well & it never leaked oil.

Steve.

[Brian WoodParticipant @brianwood45127]

AJAX,

I don't know what the melting temperature is for the rods I used, I made up some cranked carriers in thin aluminium box section to hold a starter switch out over the back of a lathe. It has worked well.

As others have said, do the job using the instructions supplied and without doing any vee prepping, just flow the metal into the joint..

I think you will be pleased with the result

[BazParticipant @baz89810]

I bought some of the rods that were being demonstrated at the Harrogate exhibition quite a few years ago, I used them to build up a couple of Sweet Pea loco smokebox saddles that had been fettled way too much and there was nothing to machine. This stuff built the edge up beautifully and stayed put through subsequent machining operations

[Ronald MorrisonParticipant @ronaldmorrison29248]

Posted by AJAX on 01/05/2022 21:00:42:

Posted by Pete Rimmer on 01/05/2022 18:22:25:

I'd tig weld that for you if you were able to bring it to me in N Kent.

Pete, that's very kind of you to offer; however, I'm going to get some brazing rods and give it a try on some scrap. I'd like to see if I can do it myself as it could be a useful skill for future tasks.

The aluminum brazing rods will probably do everything you need for this repair. However, do be aware that this is an irreversable repair. Once done, TIG welding is no longer an option. The area to be TIG welded would be contaminated by the brazing rod.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I've got some Taymar 3520 & 3530 which were in a clearance sale in one of the big DIY stores, there is no melting temperature on them, but Farnell have the same numbers in their list which may give you an idea Alloy repair rods I've also got some GoGas AR2423 ones as well which Cromwell have GoGas repair rods I've had these for several years, but never used any of them, so I can't vouch as to how good they are or not.

Here's the instructions for the AR2423 ones.

Regards Nick.

Edited By Nicholas Farr on 02/05/2022 11:52:41

[BazyleParticipant @bazyle]

As this is Al can this kind of job be done with simple propane rather than acetylene or is the heat too diffuse?

[Brian WoodParticipant @brianwood45127]

Bazyle,

A propane flame is quite hot enough, no need for oxy-acetylene, that might meld the part you are trying to repair.

Brian

[AJAXParticipant @ajax]

I thought it might be useful to give a quick update.

I bought some cheap "aluminium brazing rods" with a claimed melting temperature of circa 390 degrees. Not having used any before, I gave them a quick try on some scrap aluminium – an extruded finned aluminium heat sink from a power supply. I started off gently but found I had to turn up the gas to reach a suitable temperature which I checked with a non-contact thermometer. The brazing/soldering worked just fine and gave a good looking joint. I was quite impressed.

Buoyed by my initial success with the heat sink, I turned my attention to the broken casting. Lucky I was paying attention as the casting had a much lower melting temperature! I had barely started before it visibly softened. There was no chance of the rod melting at that temperature so I abandoned the job before it vaporized. I'm guessing it was an aluminium / zinc alloy.

The casting has now been drilled and screwed together, with a good dose of strong epoxy. I'm quite happy to have tried the brazing rods and I would use them again given a suitable material.

[AJAXParticipant @ajax]

Posted by Brian Wood on 02/05/2022 12:40:56:

Bazyle,

A propane flame is quite hot enough, no need for oxy-acetylene, that might meld the part you are trying to repair.

Brian

Even propane was hot enough to melt the broken casting.

[noel shelleyParticipant @noelshelley55608]

Propane is more than hot enough and great care is needed to control the heat and get the rod / work to flow. I would say that you had TO MUCH heat. The heating is VERY critical. Noel.

[not done it yetParticipant @notdoneityet]

There is very little load on that piece, when tightened down – using suitable washers. It’s basically here as a means of providing a ‘pivot’ – like hold-down kits for holding bits on milling machine tables.

[AJAXParticipant @ajax]

Posted by noel shelley on 06/05/2022 21:40:27:

Propane is more than hot enough and great care is needed to control the heat and get the rod / work to flow. I would say that you had TO MUCH heat. The heating is VERY critical. Noel.

Too much heat for the casting but not enough for the rods I was using. That's why I decided they were unsuitable for this job. And as "not done it yet" suggests, there will be minimal load on this part so I'm happy with my screwed and glued repair.

[Clive FosterParticipant @clivefoster55965]

AJAX makes a good point about matching the melt temperature of these aluminium "brazing" rods to the that of the alloy being repaired.

Its many years since I used the Lumiweld branded ones I bought not too long after they first appeared on the open market but I recall coming very close to disaster on the second job. Which almost ran away from me but a bit of plumber style wiping saved the day. Looked to be a pretty basic sand cast aluminium too.

Its very easy to overlook the fact that the melt point depressing effect runs into the component being repaired. As you are heating the the main body of the part just behind where the repair is to be made once the break surface is hot enough for the rod to start melting and depressing the melt point of the part itself so fusion can begin the temperature behind the break will be "too high".

So the melt zone proceeds apace if rod melt temperature and body material melt temperature are too close.

The cure is to lift the heat away from the junction before the main body starts to collapse. But if the rod temperature is too close to the material melting point it's darn difficult to reduce heating by the right amount quickly enough.

The first job I did was on an alloy with a decently higher melting point than the Lumiweld rods. Worked like a charm. Just like the instructions said. So I got overconfident and the second job proved things weren't so simple.

Not a job I'd do for othr people! The rods I have left are for me only.

Clive

[not done it yetParticipant @notdoneityet]

These lumiweld, and other, matetials are the same, or very similar to Birmabright. Landrover aluminium body panels were relatively easily repaired with patches. The requirement was to oil the surface of the panel and heat carefully until the oil vapourised, at which point the panel was getting close to melting point and the repair could be carried out satisfactorily with a little (or a lot of) practise.

If the motor mounts were die-cast in cheap ZAMAK (MAZAK), the melting point would be lower than the filler material, so no chance of making a decent repair.

Edited By not done it yet on 07/05/2022 10:35:50

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