W O R K S H O P
SINGLE-SIDED
JOINING OF STEEL
AND ALUMINIUM:
LOW HEAT INPUT FOR STABLE WELDED JOINTS
The thermal joining of
different materials such
as steel and aluminium
is of crucial importance
in automotive lightweight
construction. However, this process
is particularly challenging due to
the different physical and chemical
properties of the materials. It is
difficult to achieve high-quality,
stable results and the options for
further working of the semi-finished
parts are significantly restricted.
The solution to these challenges is a
welding process with reduced heat
input – the cold metal transfer (CMT)
process developed by Fronius.
The low level of spattering coupled
with the constant and extremely
stable arc deliver optimum welding
results. International automotive
industry supplier Magna Steyr
has taken CMT and developed a
technology that not only makes it
possible to manufacture bodywork
parts much more cost-effectively,
but also allows weight savings to be
achieved too.
Car body manufacturers in the
automotive industry are increasingly
relying on a combination of different
materials – and with good reason.
The weight of the vehicles can be
36 September 2018
In the CMT welding
process, the arcing
phase is kept very
short and the heat
input reduced. Using
this process, the
energy input can
also be continuously
adapted to suit the
component to be
welded.
materials, such as their thermal
elongation, heat conduction and
corrosion resistance, must be taken
into account. These have a negative
effect on the quality and strength of
the welded joint. The formability in
subsequent production processes
is also very limited.
The reason for this restricted
formability lies in what is known as
the intermetallic phase, which forms
where the two materials touch and
fuse together when they are welded.
This layer is brittle and susceptible
to cracks and pores, which impairs
the stability of the joint. International
automotive industry supplier
Magna Steyr was keen to address
this problem. The company, which
is headquartered in Graz, Austria,
develops and produces individual
components and complete vehicles,
and uses lightweight construction
methods for its vehicle bodies. In
order to lower the production costs
for steel-aluminium weldments,
Magna Steyr examined the joining
process in great detail and came to
the conclusion that the temperature
has a critical influence on the weld
seam quality.
A ‘COLD’ WELDING
PROCESS IMPROVES
THE STABILITY
The heat input during welding plays
a significant role in determining
the thickness of the intermetallic
phase. In the trials carried out by
engineers, Magna Steyr discovered
that ideally this should not exceed
ten micrometres to ensure the joint
is stable. To achieve this, the experts
had to control the temperature
progression in an optimal manner,
keeping it above the melting
temperature of aluminium but below
the vaporisation temperature of the
zinc layer applied to the steel plates.
In most arc-welding processes, this
is simply not possible, but Magna
REN185
reduced considerably by using
materials such as aluminium or
fibre-reinforced plastics, which has
a positive effect on performance
and fuel consumption. It would
also be hard to meet the ever
more stringent exhaust emission
regulations without these advances
in lightweight construction. Modern
vehicles therefore tend to have an
ingenious mix of materials, right
down to the finest details – every
individual part is designed to be
as light as possible yet still provide
optimum functionality. However,
joining these materials, with their
very different properties, poses a
huge challenge.
RESTRICTED STRENGTH
AND FORMABILITY
Steel and aluminium is one of the
most frequent combinations of
materials to be joined in automotive
lightweight construction. To reduce
costs, manufacturers weld flange
components made of aluminium
to galvanised steel plates, so
that they can be joined using the
conventional, cost-effective spot
welding process on the bodyshell
production line. However, the
different physical and chemical
characteristics of these two