Effects of welding parameters on electrode element diffusion
during micro-resistance spot welding
Xing Peng Gao
Xiao Kang Yue
G. Q. Tong
Received: 2 April 2017 /Accepted: 24 October 2017 /Published online: 11 November 2017
Springer-Verlag London Ltd. 2017
Abstract Copper electrodes are commonly employed in
micro-resistance spot welding (MRSW), a dominant process
used to join ultra-thin metallic sheets. During welding, some
copper from the electrodes inevitably diffuses into the spot
welds, changing the chemical compositions and properties of
the resulting welded joints. In this study, 0.05-mm-thick Ti
alloy metallic sheets were welded via MRSW under various
combinations of welding parameters (ramping time, welding
time, holding time, welding current, and electrode force). The
effects of these welding parameters on electrode elemental
diffusion were investigated via elemental analysis. Elemental
composition of welded joints was measured via energy-
dispersive spectrometry after tensile-shear tests. No copper
was detected in the heat-affected zone or base material, but
the amount of copper in the welding nuggets varied signifi-
cantly with the welding parameters. Moreover, comparing cop-
per element and hardness maps in weld nugget, the welding
nugget hardness increased when more copper diffused into it.
Keywords Micro-resistance spot welding
Micro-resistance spot welding (MRSW) is used to join ultra-
thin metallic sheets with thicknesses of 0.2–0.5 mm [1, 2].
Heat generation during resistance spot welding (RSW) is giv-
en by the following equation:
Q ¼ I
where Q is the heat generated (J), I is the welding current (A),
R is the resistance (Ω), and T is the duration of current appli-
cation (s). R is related to the force used to apply the electrode.
The electrode application force and welding current pro-
files used during different portions of the MRSW process are
shown in Fig. 1. Several scholars have studied MRSW as its
use has increased in areas such as the electronic, automotive,
and aerospace industries [3–6].
Copper electrodes are often used in RSW [7–11]; however,
electrode degradation during welding is inevitable. E.
Gauthier et al.  pointed out that in the case of Zn-coated
steel, continuous alloying occurs between the molten zinc and
the electrode surface. This accelerates electrode erosion. S.J.
Dong  studied the effects of composite coatings on tip life
and the mechanisms by which the coatings work. J. Peng et al.
 developed an imaging approach that quantitatively deter-
mines the electrode degradation status during aluminum
RSW. Because the sheets welded in these studies were thick,
this research considered only electrode degradation.
Elemental diffusion from the electrode tip to the welding zone
was ignored. Unlike with typical resistance spot welding, el-
emental diffusion causes a significant change in the chemical
composition of the welding zone during MRSW. This is re-
ferred to as a size effect. By comparing reports from M. Vural
, F. Karcı , D. Kianersi , A.M. Pereira , and P.
Penner , one can determine that welding nuggets (WNs)
with the same diameter but different chemical compositions
have different peak loads and micro-hardnesses. Changes in
composition of the welding zone affect the properties of
welded joints, and thus, it is important to research diffusion
from copper electrodes to the welding zone during MRSW.
* Feng Chen
College of Mechanical and Electrical Engineering, Nanjing
University of Aeronautics and Astronautics, 29 Yudao St.,
Nanjing 210016, China
Int J Adv Manuf Technol (2018) 95:1597–1606