Durafix aluminium rods

[Fooman]

How strong is the joint? It looked more like brazing than welding,definatly a lower temp than normal alloy welding.But I liked his technique...the swishing/wiping motion,I must try that next time I try alloy welding.

The US webpage (www.durafix.com) states that it welds zinc alloys and brazes aluminium alloys. This suggests that it is a zinc alloy. Somebody has stated the composition at 94% Al, 6% Zn, but that doesn't work with the quoted temperature (solidus for that composition at ~ 600 deg C). 94% Zn and 6% Al gives a eutectic at 381 deg C according the Al-Zn phase diagram in front of me.

If the connection is design such that there is plenty of area and is nice and smooth as per a brazed joint (e.g. lap joint), then it should be no problem. Corrosion may be an issue (e.g. galvanic corrosion) with the difference in compositions.

There are aluminium alloys out there for brazing aluminium, but they are at a higher temp (~570 deg C for Al-Si brazing alloys) which is closer to the melting point of the major aluminium alloys (~595 to 650 deg C), so temperature control has to be greater, especially if you want to avoid incipient melting or unwanted age hardening.

Another thing to note about brazing, is that it is not just low temperature applications. Gas turbine blades are repaired using brazing (especially single crystal blades) and the melting point of the brazes (~1100 deg C) is not much higher than the operational temperature (900-1000 deg C) of those blades. It's expensive to do, but at ~ $5000 to $10000 per blade, there is plenty of incentive to do a expensive repair rather than a more expensive replace.

Cheers,
FM

[Brian d marge]

The US webpage (www.durafix.com) states that it welds zinc alloys and brazes aluminium alloys. This suggests that it is a zinc alloy. Somebody has stated the composition at 94% Al, 6% Zn, but that doesn't work with the quoted temperature (solidus for that composition at ~ 600 deg C). 94% Zn and 6% Al gives a eutectic at 381 deg C according the Al-Zn phase diagram in front of me.

If the connection is design such that there is plenty of area and is nice and smooth as per a brazed joint (e.g. lap joint), then it should be no problem. Corrosion may be an issue (e.g. galvanic corrosion) with the difference in compositions.

There are aluminium alloys out there for brazing aluminium, but they are at a higher temp (~570 deg C for Al-Si brazing alloys) which is closer to the melting point of the major aluminium alloys (~595 to 650 deg C), so temperature control has to be greater, especially if you want to avoid incipient melting or unwanted age hardening.

Another thing to note about brazing, is that it is not just low temperature applications. Gas turbine blades are repaired using brazing (especially single crystal blades) and the melting point of the brazes (~1100 deg C) is not much higher than the operational temperature (900-1000 deg C) of those blades. It's expensive to do, but at ~ $5000 to $10000 per blade, there is plenty of incentive to do a expensive repair rather than a more expensive replace.

Cheers,
FM

Agreed the key is design the Joint , for large area , keep the loads low .. ie non critical areas and it would be fine and one assume that the area should be clean !

Me I trundle round to the local welder and put on my sad face ......

Stephen

[Motu]

Yes,brazing is a stronger joint than many realise - all the British frames were brazed.And even Rickman brazed their Reynolds 531 frames rather than welding,they said welding damaged the metal.

A lot is opperator experiance.I have a Henrob welding torch,and have seen the demos live - pretty impressive welding coke cans and unheated unprepped cast iron with a piston ring,hard facing with a hacksaw blade.I have attempted all those,and yes it can be done....but I'd need a shit load of practice behind closed doors before I could pull it off.

[imdying]

Coke can looked a bit too easy to me... took Phil 3 goes before he could do a mint job So yeah, pretty darn easy!

Should give him some cast iron, that'll mess him up

[pete376403]

Yes,brazing is a stronger joint than many realise - all the British frames were brazed.And even Rickman brazed their Reynolds 531 frames rather than welding,they said welding damaged the metal..

Most (if not all) of those brazed joints were spigot (?) type, where the tube is inserted into a socket, which gives a very large contact area compared to a butt join. If you had to join steel with a butt joint, arc welding would be preferable (and far more suited to mass production using robot welders)

[laRIKin]

The way I was trained.
All brazing joints must be lapped. (to get a good surface area, a thick material butt joint maybe OK)
And to me it is brazing and not welding.
I'm not saying that is a bad product, but the terms they are using are misleading.

[imdying]

Most (if not all) of those brazed joints were spigot (?) type, where the tube is inserted into a socket, which gives a very large contact area compared to a butt join.

That's how I plan to make my subframe. Good mechanical join, less reliance on the braze.

And to me it is brazing and not welding.
I'm not saying that is a bad product, but the terms they are using are misleading.

Agreed.

[jonbuoy]

Got some of these in the post today - even having a quick go with scrap ally I'm impressed by how strong lap joints are with this stuff. I did get it to break but only by flexing the ally 3-4 times first.

[Macktheknife]

Got some of these in the post today - even having a quick go with scrap ally I'm impressed by how strong lap joints are with this stuff. I did get it to break but only by flexing the ally 3-4 times first.

Be good to know how you feel about it in a couple of weeks when you have had a good play with it.