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Electrolytic Welding and Sintering

IP.com Disclosure Number: IPCOM000106915D
Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 3 page(s) / 135K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR [+2]

Abstract

This process provides a means of welding or sintering electrically conductive materials at temperatures low compared to their melting points. Two metal members are joined using an electrochemical solution for deposition rather than melting and solidification. This invention makes use of constriction induced local electrodeposition (*). The welding method will be illustrated for joining copper.

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Electrolytic Welding and Sintering

       This process provides a means of welding or sintering
electrically conductive materials at temperatures low compared to
their melting points.  Two metal members are joined using an
electrochemical solution for deposition rather than melting and
solidification.  This invention makes use of constriction induced
local electrodeposition (*).  The welding method will be illustrated
for joining copper.

      The two copper parts to be joined are cleaned in dilute nitric
acid.  A slurry is prepared consisting of 20 gm of 325 mesh copper
powder, 5 gm of Cu(NO3)2 .6H2O and 2 cc of H2O.  The slurry is placed
between the copper parts and the parts are clamped so as to squeeze
the slurry between the parts.  An AC current with a frequency equal
to or greater than 60 Hz is passed through the slurry and the voltage
drop across the joint is monitored.  Initially, the voltage drop
across the joint was high, indicating high electrical resistance in
the joint.  When sintering began, the voltage drop rapidly decreased
to 0.5 V, then continued to decrease more slowly to 0.2 V over the
next minute or so.  After this treatment, the two copper parts were
observed to be "welded" together.  The resulting electrolytic weld
was difficult to pull apart.  The copper powder was well sintered in
the joint and had the color of copper metal.

      The mechanism of electrolytic welding and sintering is thermal
gradient induced electrodeposition.  The copper particles, when
packed together, form a large number of small area contacts.  The
solution, which is an electrolyte, fills the interstices between the
particles.  When an AC current is passed through the slurry, the
contact points heat up more than the bulk of the particles.  The
temperature gradient thus created drives an electrochemical cell
causing copper to electrodeposit at the contact points between the
grains so that they sinter together.  At the same time, copper
dissolves from the cooler portion of the grains to maintain charge
neutrality.  It is also important that the current is pure AC; and DC
bias will cause plating on one side of the constriction and
simultaneous dissolution on the other side.  In electrolytic welding
the powder compact does not become fully densified but it is
mechanically strong and has a high electrical conductivity. The heat
generated by the AC current eventually evaporates the water and
decomposes the Cu(NO3)2 .6H2O to CuO which deposits in the
intersticies between the particles.

      This method of welding has a number of advantages over
conventional welding, brazing, or soldering.

      When making electrical contacts, soldering has the disadvantage
that it creates bimetallic couples that are subject to galvanic
corrosion.

      With respect to welding copper, the thermal conductivity of
copper is so high it is virtually impossible to weld by conventional
means.

      In general, the high te...