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A feature of each of the recommended alloys is the low temperature
at which it can be used for making joints between metals with
which they are compatible, which are generally thosewhere
tin-lead solders can be used (though they should not be regarded
merely as substitutes for tin-lead). The low specific heat
and latent heat of fusion to make it possible to solder close
to many materials without causing undue thermal expansion
or distortion. The volume changes, both during and after solidification,
are very small.
The viscosity and surface tension are also very low, making
for easy flowing. The adhesion and mechanical strength in
the finished joint depend on developing a good working technique
for the particular task, as well as choice of a suitable flux
(the resin-based acid fluxes are usually satisfactory).
By judicious selection of the alloys, the working temperatures
can make possible successive solderings in close proximity,
while not affecting the quality of the neighbouring joints.
Overlap or contact, which carry the risk of significant alteration
of the properties of both alloys at the site, should be avoided.
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