Note: Descriptions are shown in the official language in which they were submitted.
~5~L693
The invention relates generally to the brazing of articles
containing aluminum.
The German Auslegeschrift 1,962,760 discloses a brazing
alloy consisting of 4 to 20 percent by weight of silicon and 0.01 to
10 percent by weight, preferably 0.05 to 2 percent by weight, of the
elements of the group composed of bismuth, strontium, barium and anti-
mony with the remainder consisting oE aluminum and impurities due to
the production of the alloy. This publication teaches the use of the
brazing alloy as a filler metal for the fluxless brazing of alum-
inum-containing articles in a non-oxidizing atmosphere or in a low
vacuum.
The German Offenlegungsschrift 2,143,965.6 also discloses
a brazing alloy for the fluxless brazing of aluminum-containing ar~
ticles which likewise consists of 4 to 20 percent by weight of silicon
and 0.01 to 10 percent by weight, preferably 0.05 to 2 percent by
weight, of the elements of the group composed of bismuthl strontium,
barium and antimony with the remainder consisting essentially of a-
luminum and impurities due to the production of the alloy. The char-
acteristic of this alloy resides in the fact that, instead of or
together with the bismuth, strontium, barium and antimony, it contains -
beryllium in amounts of 0.00001 to 1.0 percent bysweight and, prefer-
ably, in amounts of 0.0002 to 0.1 percent by weight.
The foregoing brazing alloys have been found to yield good
results in practice. However, they possess the disadvantage that they
impose relatively stringent requirements as regards the presence of a
non-oxidizing atmosphere or a low vacuum during the brazing operation.
A general object of the invention is, therefore, to provide
a novel process and a novel brazing alloy for the brazing of aluminum-
containing articles.
A further object of the invention is to provide a process
and brazing alloy which enable aluminum-containing articles to be
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1 brazed more economically than was possible heretofore.
Another object of the invention is to provide a process
and brazing alloy which enable aluminum-containing articles to be
brazed in a simpler manner than was possible until now.
An additional ob~ect of the invention is to provide a
process and brazing alloy for brazing aluminum-containing articles
which enable higher quality ~oints to be achieved than was possible
heretofore.
It is also an object of the invention to provide a pro-
cess and brazing alloy for brazing in a non-oxidizing atmosphere
or in a low vacuum which enable the requirements imposed on the bra-
zing atmosphere by the conventional brazing alloys to be lessened.
In accordance with the foregoing objects and others which
will become apparent, the invention provides, as one of its features,
in a process of brazing aluminum-containing articles, for the step
of brazing the articles with an aluminum-silicon base brazing alloy
which includes at least one substance selected from the group con-
sisting of sodium, potassium and lithium. This permits a relaxation
of the requirements imposed on the brazing atmosphere from those im- ;
posed when using similar brazing alloys which are free of sodium,
potassium and/or lithium.
The brazing alloy according to the invention may include
about 4 to 20 percent by weight of silicon, about 0.01 to 10 percent
by weight, preferably 0.05 to 2 percent by weight, of at least one
of the elements selected from the group composed of bismuth, stron-
tium, barium and antimony and O.OOOOl ~to 1.0 percent by weight, pre- -
ferably 0.0002 to 0.1 percent by weight, of beryllium with
the balance of the alloy being essentially aluminum. It is also
possible for at least one of the elements bismuth, strontium, barium
and antimony to be present without beryllium or, conversely, for
'~.
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beryllium to be present without any ~f the elements bismuth,
strontium, barium and antimony being present.
One of the important features of the invention resides in
the presence of at least one of the elements sodium, potassium and
lithium. The elements sodium, potassium and/or lithium may be pre-
sent alone, that is, without the elements of the group composed of
bismuth, strontium; barium, antimony and beryllium being present.
Advantageously, however, the elements sodium, potassium and/or li-
thium are present together with one or more of the elements bismuth,
strontium, barium, antimony and beryllium. The brazing alloy in
accordance with the invention may contain about 0.0001 to 1.0 per-
cent by weight of at least one of the elements selected ~rom the
group consisting of sodium, potassium and lithium. Preferably, the
brazing alloy contains about 0.005 to 0.1 percent by weight of at
least one of the elements of the group composed of sodium, potas-
sium and lithium.
The remainder of the brazing alloy may consist entirely
or predominantly of aluminum and impurities conditioned by the pro-
duction of the brazing alloy, that is conventional impurities.
According to the invention, the brazing alloy may be used
for the fluxless brazing of aluminum-containing articles in a non-
oxidiz~ggatmosphere or in a low vacuum. A non-oxidizing atmosphsre
may be provided by blanketing the region of joining with a suit-
able protective gasu For instance, an inert gas such as argon may
be used for this purpose. It is also possible to use other gases
such as, for example, nitrogen and ammonia.
Research has shown that, when using the brazing alloy in
accordance with the invention, it is no longer necessary to impose
such stringent requirements on the oxygen content of the brazing
' l~S1693
atmosphere or on the degree of the vacuum used for brazing as were
required heretofore. Simultaneously, the results achieved when us-
ing the invention are identical to or better than those achievable
in accordance with the earlier-mentioned German publications.
The addition of alkali metals as according to the inven-
tion has been found to provide esp~cially favorable effects as re-
gards the corrosion-resistance of the brazed joint and, in particu-
lar, under those conditions where moisture has access to the joint.
This is particularly true in those instances where, aside from one
or more alkali metals, the brazing alloy additionally includes
beryllium.
If the corrosion-resistance is denoted with values from
O to 5 with the value O representing the ideal condition or, in
other words, a condition which is practically inachievable, that
is, with the value O representing the bo.st corrosion-resistance and
the value 5 representing the poorest corrosion-resistance, then the
following values may be assigned to the test samples which were run:
the samples with additions of beryllium and alkali metal, l; test
samples without beryllium but with alkali metal, 2; and test samples
with neither beryllium nor alkali metal, 3.
It has been found advantageous when the tota~ ~uantity of
the alloying elements bismuth, strontium, barium, antimony, beryl-
ium and sodium in the brazing alloy is at most about 10 percent by
weight.
The appended Table sets ~orth several examples of brazing
alloys according to the invention. It is sel~-understood that the
compositions given are merel- exemplary and are not intended to
limit the invention. The values in the Table are in terms of weight
percent and in all cases the remainder is essentially aluminum.
.~ -5-
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