Abstract
The present work encompasses studying the possibility of joining pure
tantalum to itself, to ASTM A216 low alloy steel and to pure copper
using spot soldering and spot brazing methods, and establishes a
scientific knowledge about bonding mechanism between tantalum and
other metals when joining by these methods. Resistance spot welding was
used to compare the resulted joints between the three processes.
Foils of (ASTM A63), (AWS BCu-1) and (AWS BVAg-0) were used
as filler metals. Two types of copper base electrode were used to study
the effect of electrode tip design on the resulted joints. Four different
joining times (1, 2, 3, and 4 seconds) were used to select the best joining
time.
Reflected optical microscopy test of joint assemblies was performed to
study the mechanism of joint formation, the joint strength was evaluated
by tensile shear strength test and by calculating the total work which
represents the toughness of joint.
Joint assemblies of (St-St), (Cu-Cu) and (St-Cu) were made for tensileshear test to compare the joint strength of these assemblies with that of
(Ta-Ta), (Ta-St) and (Ta-Cu) assemblies. The outcomes of these tests are:
The concentrated heating and localized joining in much shorter time are
the essential reason to form joint by using these three processes.
The best joining time was two seconds, depending on the results of
tensile-shear test and calculating of total work.
(Ta-Ta) assembly was joined successfully by these three processes with
using all filler metal types, Spot brazing using (AWS BCu-1) filler metal
gave the best joint strength.
While in the case of (Ta-St) the assembly was joined successfully by
resistance spot welding, spot soldering and spot brazing using (AWS
BCu-1) filler metal only. Best joint strength was given by resistance spot
welding.
The assembly of (Ta-Cu) could not be joining except by spot brazing
using (AWS BCu-1) filler metal.
Spot soldering and resistance spot welding are used successfully to join
(St-St) assembly and have showed the higher joint strength than other
assemblies especially in the case of joining by spot soldering method.
(Cu-Cu) and (St-Cu) could not be joined using these three methods.
Using of modified electrode gives more strength to joint which
increases the total work of joint in the case of joining by spot brazing
process using (AWS BCu-1) filler metal.