Page 197 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

182 Chapter Three

is required, a welding expert should be consulted for structural
applications.
Martensitic stainless steels are iron-chromium alloys that can be
heat treated to a wide range of hardness and strength levels.
Martensitic grades are typically used to resist abrasion. They are not
as corrosion resistant as the austenitic and ferritic types. Martensitic
stainless steels, like the ferritic, are not easily welded in structural
applications, and a welding expert should be consulted when welding.
Aluminum. Aluminum has many characteristics that are highly
desirable for engineering applications, including structural, such as
high strength-to-weight ratio, and corrosion resistance. Aluminum
does not have the high modulus of elasticity associated with steel, but
the weight-to-modulus ratio of the two materials is roughly equal.
Aluminum is readily welded, but the welded connection rarely dupli-
cates the strength of unwelded base metal. This is because the heat-
affected zone (HAZ) in the as-welded state has reduced strength com-
pared to the unaffected base material. This is in stark contrast to the
behavior of steel, where the entire welded connection can usually be
made as strong as the base material. The degree of strength degrada-
tion depends on the particular alloy system used. However, the engineer
can conservatively assume that the heat-affected zone will have
approximately one-half the strength of the aluminum alloy.
This characteristic is not necessarily a strong impediment to the
use of aluminum, however. Creative joint designs and layouts of
material can minimize the effect of the reduced strength HAZ. For
example, rather than employing a butt joint perpendicular to the pri-
mary tensile loading, it may be possible to reorient the joint so that it
lies parallel to the stress field, minimizing the magnitude of stress
transfer across this interface, and thus reducing the effects of the
reduced strength HAZ. Gussets, plates, stiffeners, and increases in
thickness of the material at transition points can also be helpful in
overcoming this characteristic.
Aluminum cannot be welded to steel or stainless steel by conven-
tional arc-welding processes. It is possible to join aluminum to other
materials by alternative welding processes such as explosion bonding.
A common approach to welding aluminum to other significantly dif-
ferent materials is to utilize explosion bonding to create a transition
member. In the final application, the steel, for example, is welded to
the steel portion of the transition member, and the aluminum is welded
to the aluminum side. While generally not justified for structural
applications, this approach has been used for piping applications, for
example. For structural applications, mechanical fasteners are gener-
ally employed; however, the galvanic action should be considered.

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