I have some 4043 aluminum rods in 1/16th and 1/8th with no flux. I have ordered the video on How To
Gas Weld Aluminum from your company. Will it tell me what kind of flux to use for propane and
oxygen/acetylene welding or brazing? I am trying to learn how to repair the thinner
aluminums. I can weld the thicker pieces with the -DC aluminum rods with flux but just can't seem
to get the gas welding down to good. If the video will not help me on the flux please advise on
what flux I need for the 4043 rods.
Also, the Alumaloy is a brand name that sells on TV which a woman illustrates and makes it look easy but
apparently there are some steps that she is leaving out. The rods do not have flux on them and they
state that you do not need flux to weld with these either in propane of oxy/acet. Please advise
PS the 4043 rods melt at 730 to 780 degrees
Thank you very much for your attention.
The Tinman Respondeth:
You can use the 4043 with flux to oxyacetylene weld thin sheet---on some alloys. Do not try to stick weld
anything under .125" thickness.
The video will help you make good sound butt welds on thin sheet using
oxy-acetylene, using the traditional methods used byindustry to manufacture and repair airplanes, cars, race
cars, and motorcycles.
Our little booklet, Aircraft Aluminum Gas Welding has a filler chart for the
alloys and their proper fillers, as well as fluxes and trouble shooting.
The 4043 filler is a low-temp filler with a high degree of brittleness, but also has a good crack-resistance
while the weld is cooling down from the molten state. Other fillers are recommended for alloys 1100,
3003, 5052, 6061, etc.
Be sure to know the alloy of the part needing repairs before attempting repairs. If you cannot identify the
alloy, I would not recommend making a "hot" repair --- unless having the part "sort of working" is more
important than either safety or longevity. Adding any molten metal as a "fix" to an aluminum part may
render it as quite useless or even as scrap, if correct procedure is not followed.
So Alumaloy is now marketing on TV? It apparently does not need a flux and is sort of a "miracle" or
"amazing" product. "the melting temperature of Alumaloy is 728 deg F.", according to the company.
The people who repair aluminum agricultural pipe here in California use this stuff. They also say it can
take a few sticks to get the hang of it, as it is "not easy".
The company also states that this product "welds, solders and brazes" aluminum. I don't want to fight with
anybody about what does what, but I will take the time to address standard industry definitions of these
three hot joining processes (see below).
By the way, I hear a lot from professional welders, craftsmen and hobbyists about different unusual joining
products out there.
Our Aero Solder for aluminum melts at 775F, (requires a flux,) and therefore, by industry standards meets
the definition of Soldering by melting below 850F.
ALCOA, in their book, Brazing ALCOA Aluminum, lists the melting temperatures for all of their aluminum
brazing alloys, by alloy, at from 960F to 1185F, and so they meet the industry definition of Brazing by
exceeding the 850F melting temperature.
In this ALCOA book, as well as in common filler-metal charts, 4043 melts at 1135F, and is used both as a
brazing filler and as a welding filler. This is why, in aluminum work, the industry has evolved the term
"braze-welding". You see, for one aluminum alloy melting at, say, 1125F, the 4043 is welding, and yet at
on a higher melting-point alloy, say 1185, it brazes. Also, if the operating temperature is not held
exactly, the joint brazes a little and welds a little as the joining temperature fluctuates over a 40
Welding, by industry standards, means that the parent metal is melted and that the filler mixes in with it.
Photomicrographs in various Aluminum Data books show sectional views of brazed joints as having a fuzzy
line where the filler joins to the parent metal. This indicates a normal diffusion or bonding layer
between the two UNMIXED alloys, and is therefore not truly a weld.
Each method, Soldering, Brazing, and Welding has benefits and/or drawbacks, IE: joint design, strength of
bond, temperature performance, and ease of application. Welding may offer the highest strength, but may
distort or perhaps melt pieces nearby. Brazing may offer good strength, but not take much shock or
bending loads. Soldering may offer low distortion and ease of application, but may not have the tensile
Solders and brazes tend to be brittle and cannot sustain any hammering, straightening, or bending without
cracking. I have had to repair many of these "fixes" (by cutting out the entire area), and they are
generally not recommended for very many aircraft or auto repairs at all.
Remember, too, that many adhesives and metal-filled epoxies have been on the market for years. I have
personally repaired castings, engines, propellors, and other solid parts very reliably with high-quality
metal-filled epoxies. And I have also repaired some leaky tanks by either brazing or soldering. I always
ask myself the question: how strong does it have to be? And, what is the operating environment? Then I
consider the repair options, along with each benefit and drawback. Because of the litigious nature of
this society, and that any aircraft, auto, or scooter repair can be subjected to intense scrutiny, one
must be excessively careful about making repairs or making recommendations to repairs.
BTW, our Historic Film,
"Alumium Welding Methods"
by ALCOA, 1941, covers gas welding, stick welding, brazing, spot welding, carbon arc, and atomic hydrogen.