This stuff has been around for decades, every so often somebody dusts it off and brings at back as the new "miracle" soldering rod. It's an alloy of tin and zinc, has to be rubbed into the mating aluminum surfaces to displace the oxide and really isn't very strong stuff. It also doesn't wick into cracks. Not welding at all, no aluminum in it, it's a solder. Probably wouldn't do what you want.
This IS a metalworking group, why not get a billet of alloy and start whittling?
I've used it quite a bit. It works, sort of, but I'm pretty sure it won't do your job. The process is more like welding than soldering, except that the stuff itself is technically a solder. Welding refers to the process of joining (usually metal) by locally melting the joint - and usually adding a filler of the same material. Soldering is the process of joining with a material of a lower melting point than the items to be joined; the items themselves do not melt. When soldering, the molten solder wets the joint and flows into it by capillary attraction, and when it freezes the joint is made. For soldering to be successful the molten solder must wet the joint, and this is where the problems start, it won't wet a dirty joint. And for most metals the very act of heating the joint makes it dirty - the oxygen in the air reacts with the hot metal to create oxide which prevents the solder from wetting and flowing. There are only two ways around this: solder in an oxygen free environment, or use a barrier to prevent the oxygen from reaching the joint. The latter is the most convenient method, and the barrier is called a "flux".
Aluminium is particularly difficult to solder because the oxide forms almost immediately at room temperature and there are very few fluxes that can get rid of it.
The "welding" rods you mention are not made of aluminium, so they don't actually weld, they also have a lower melting point than aluminium. They are used to "tin" the components of the join before bringing them together. You first clean the joint area with a stainless steel brush then heat it until the tip of a rod melts when it touches it. You then spread the molten rod material over the joint area with a thin stainless steel rod, making sure to scratch the joint - this removes some oxide and the molten solder itself prevents further oxidisation. Keep scratching through the molten solder until you're happy you've removed all the oxide, then remove the heat and allow the solder to freeze. You do this for all the components of the joint. You then bring the components together and reheat the joint until the solder melts again, remove the heat and the joint is made. A flux is not used because the solder itself doesn't readily oxidise.
You can now appreciate that this method will not allow the solder to flow into a crack. The solder itself is quite strong - stronger than most aluminium alloys, so you could use it to fill a crack that has been "prepped" into a V-groove. But there is an additional problem: a lot of aluminium alloys are heat treated and the act of heating to melt the solder is likely to anneal (soften) it so much as to make it no use for its intended purpose.
You oughta see the guys at the MN state fair work with this rod! They do GREAT things. But take it home and try it yourself????? Maybe, if you are already an accomplished welder who also understands brazing very well. There are at least 2 kinds, the last I knew. One kind REQUIRES the stainless steel brush (which comes with the packet of rod). The other kind supposedly does not. Sorry but I don't rememeber why not.
A funny story for y'all on the subject:
I did buy this rod many years ago. The package of about 20 1/8" diameter rods about 18" long, with SS brush, cost me $30. I kept it around for years looking for an application. My old Cub Cadet developed a head gasket leak right beside the exhaust valve and by the time I noticed it, the hot gases had burrowed a groove in the aluminum head. Got a new gasket and found that the new head was gonna be $60, so decided to give the rod a try, Vee'd out the crack, brushed it well and did the soldering. Looked great. "Milled" it flat on a surface plate/ sandpaper and reinstalled it. Worked like a champ!!! Went back to mowing. Once the head got up to temp, the whole slug of whatever it is came flying right out of there in a molten state.
Not going to work in that application - it's like soft-soldering it with tin. Won't handle the same stresses that the parent metal does - or in your case didn't.
Plan A: Call Hohner and see if you can order a replacement neck. You probably aren't the first one that has this problem, and they often revise the design when these sorts of flaws appear. And even if it sounds expensive, it's probably less than a proper repair.
If that fails and it's still worth the effort to save that guitar, you need to totally disassemble the neck from the body and find a true "artiste" with a TIG welder. Because the spread between 'welding temperature' and 'big puddle of molten aluminum all over the bench temperature is VERY slim - meaning a high screw-up potential.
You need someone who TIG welds on delicate things like $50,000 injection molds (or similar) all day. I know only one someone like that, if he hasn't died or retired & gotten totally out of practice...
Sometimes you can put a clay "Tinker's Dam" around the item so if it does melt more than expected it is contained and can still be saved cosmetically - but it'll never really play the same. Especially the fretboard, too much precision is required - if it shrinks or stretches any in the fixture you'd have to re-machine the whole neck and re-cut all the fret slots, or the relative tuning goes away.
My best guess at a fix procedure would be to cut open and clean out the cracks with a hacksaw, and stop-drill across at the root of the crack so it can't propagate any more. Then make sure it's bent straight and true, and devise a metallic clamping fixture to hold both ends of the neck rock-solid in the right position. (And make sure the fixture can take some serious heat, as it's all going into an oven.) Then scrub out the crack with flux and a stainless wire brush.
The welder will have to pre-heat the whole casting & fixture in an oven, then clean out and flux the crack area again, and fill in the entire crack in several passes with TIG weld filler metal. After that, you have to clean up the outer welded surfaces with files, grinders and sanders, and buff it out smooth. And repeat any heat treat and/or anodizing steps to restore the strength and appearance.
The weld filler is a slightly different composition and is not going to take anodize or finish the same as the base metal, but you should be able to make it 'not obvious'.
First you need to know the alloy used. Many aluminum alloys are NOT weldable even under the best of conditions. Some also can not be heat treated and will never have adequate strength after welding as they need to be work hardened. Many forged parts would be in this category. (Think billet)
It's also surprising just how strong one of those torch filler joints CAN be. The stuff is harder than the base metal in many cases but you would need to "V" it out to get any strength and I don't think this is really a good aplication for it.
Price the replacement part first, then decide how much/little you want to spend trying to save the old part, and what your risk tolerance is.
If not too expensive, but more than you REALLY want to spend, you might want to risk trying a DIY repair first, and if it does not work, order the new paert.
On Sun, 16 Mar 2008 12:50:38 GMT, with neither quill nor qualm, "Carl Byrns" quickly quoth:
What, you've never heard of Weldwood products?
-- Shake off all the fears of servile prejudices, under which weak minds are servilely crouched. Fix reason firmly in her seat, and call on her tribunal for every fact, every opinion. Question with boldness even the existence of a God; because, if there be one, he must more approve of the homage of reason than that of blindfolded fear. -- Thomas Jefferson
Unfortunately, I do not maintain the FAQ, only post a periodic pointer to it. To add something like this to the FAQ, contact Jim Kirkpatrick. I honestly don't know if he is still handling any of it though. His address is provided near the top of the FAQ at:
The last contact I have had with him was a little over 4 years ago.