Brazing Alloy: BAg-5 versus BAg-34?

What criteria do I use to select one brazing alloy versus the other?
I've been using AWS BAg-34 for joining a variety of metals ever since
I purchased my torch about a decade ago and have a good supply of this
particular alloy on-hand.
This past weekend, I received an impressive quantity of AWS BAg-5
alloy as a gift from a family member. I now need to learn more about
brazing alloys...
I've been looking at the spec. sheets for the products I have on-hand:
formatting link

The DESCRIPTION, PROPERTIES OF BRAZED JOINTS, and APPLICATIONS for
both seem to be very similar, which does not answer my question: How
do I decide whether to use AWS BAg-5 or AWS BAg-34 for a given task,
now that I have a choice of selecting one from these two brazing
alloys?
From the documentation, the main difference seems to be that AWS
BAg-34 has 2% tin while AWS BAg-5 does not. I have no clue what the
significance of this is other than a hazy recollection of reading
somewhere that the addition of tin gives the molten alloy wetting
properties to make it flow better into the joint; hence, my choice of
BAg-34 as a general purpose brazing alloy at the time, plus the fact
that my local welding supply shop had plenty of it in-stock all the
time and recommended it. This still doesn't answer the question as to
when or why one would select AWS BAg-5 over AWS BAg-34 when BAg-34
seems to have better properties due to the tin in it.
Last night, once again, my local welding supplies shop confirmed that
both will do the job but, AWS BAg-34 is "better" than AWS BAg-5 based
on their own personal experience of using the product without
quantifying what "better" means. The fact that AWS BAg-5 is out
there on the market along with AWS BAg-34, suggests that I am missing
some information and/or don't quite comprehend something. Can anyone
enlighten me? If AWS BAg-34 is "better", why do they make AWS BAg-5?
How do I determine when to use it other than reading a specification
off a blueprint for some fabrication project?
The manufacturer's product specification sheets for comparing the two
alloys aren't of much help for someone who doesn't know enough about
metallurgy to grasp the significance of a 2% difference of this metal
or that metal in the alloy composition. Can something like this be
explained in plain English?
One partial explanation I've gotten so far is that AWS BAg-5 needs to
be used for brazing stainless steel food industry equipment without
any further explanation as to why. It is not clear to me whether BAg-5
is preferred in this case because the material to be joined is
stainless steel or, because BAg-5 is non-toxic when used in food
processing equipment or, simply because of some ethnic tradition in
the restaurant industry that I might not be aware of. Where do I find
basic information like this? Are there any "How to Select a Silver
Solder for Dummies" books I could refer to?
Or, is all of this subjective and the choice of brazing alloy is a
matter of personal preference based on personal experience the way one
would select a 6013 rod while someone else would select a 6011 rod for
a given arc welding task -- the end result being the same -- two
pieces of metal joined together?
The more I research this, the more confused I seem to get. Is there
some sort of rule-of-thumb, expressed in ten words or less, that
someone with a hot torch and little knowledge of metallurgy could use
to make the selection?
Reply to
Speechless
Loading thread data ...
Rule of Thumb - use the lowest cost braze alloy that works well enough.
Some other considerations are resistance to corrosion and compatibility with the metals being joined.
I don't work with either one of these alloys but there is some information on the alloys I do work with at:
formatting link
(Typical Internet advice- the guy says he doesn't know anything then keeps going)
I would expect the BAg-5 to give a stronger joint but that the Bag-34 would wet better.
A lot of these alloys are used depending on factors such as heat treating after brazing and appearance of the finished joint. The FDA regulates braze alloy for food equipment. Tin cans aren't really tin because of the reactivity.
The extra 7% silver will add about $0.50 to the cost per ounce.
Generally less zinc is better because of "metal fume fever". Zinc fumes out of the alloy at relatively low temperatures, much below the melt point. Don't breathe the fumes. See
formatting link
for pictures of zinc boiling ina finished joint.
BAg - 34 is probably "better" because it wets more easily. Wetting can be greatly improved with proper surface preparation.
formatting link
Are you using Black flux? It is generally much more forgiving with a torch.
BAg - 5 BAg - 34
BAg - 5 45% silver, 30% copper, 25% zinc Solidus 1225F Liguidus 1370F Brazing Temp range 1370 -1550
BAg - 34 38% silver, 32% copper, 28% zinc, 2% tin Solidus 1200 Liguidus 1330 Brazing Temp range 1330 - 1550
Here is the little the AWS official book gives:
A7.1.7 BAg-5 and -6 brazing filler metals are used especially for brazing in the electrical industry. They are also used, along with BAg-7 and -24, in the dairy and food industries where the use of cadmium-containing filler metals is prohibited. BAg-5 is an excellent filler metal for brazing brass parts (such as in ships piping, band instruments, lamps, etc.). Since BAg-6 has a broad melting range and is not so free-flowing as BAg-1 and -2, it is a better filler metal for filling wide joint clearances or forming large fillets.
A7.1.25 BAg-34 brazing filler metal is a cadmium- free filler metal with free-flowing characteristics. The brazing temperature range is similar to that of BAg-2 and BAg-2a, making it an ideal substitute for these filler metals.
P.S. these are darned fine questions. About half the consulting work I do is because people don't' ask questions this good. The other half is because the knowledge isn't generally available.
Fell free to call if you have a question. Tom Walz at 800 346-8274 It is Thursday, December 22 and apparently everyone else is off for Christmas already.
tom
Reply to
president
Speech,
I just did the same suearch deal.
Try
formatting link

and
formatting link
That one has a heap of videos on brazing.
Happy Holidays.
Blueraven
Reply to
Blueraven
Thank you very much!!! This is the kind of info I've been looking for.
Yes, I wouldn't be without it.
Reply to
Speechless

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.