Page 3 - HIWT Winter 2012 World of Welding

hiwt@welding.org HOBART INSTITUTE OF WELDING TECHNOLOGY

Weldability of Metals Creates KnoWledge

Welders

By André A. Odermatt by drawing heat away from the device and dissipating the heat
into the surrounding air either through fan cooling or
convective heat transfer.) Aluminum conducts heat six times
faster than steel. This is another reason why welding aluminum
Many years ago, earlier in can be more problematic than welding steel. This difference in
my career, a request was thermal conductivity requires higher heat input. As aluminum
made to design lighter is heated to its melting point of about 1,200 F, there is no color
welding machines; one person change because it is highly reflective to visible light and heat.
suggested using aluminum This makes it difficult to judge when aluminum is approaching
instead of steel for the its melting point.
transformer and reactor cores.
Materials that are not affected Many industries are using stainless steel. As with other
by magnetic fields are materials, there are several categories of stainless steels
considered non-magnetic. with different characteristics. As an example, the thermal
Aluminum is non-magnetic; steel on the other hand is affected conductivity of stainless steel is about 1/3 the rate of plain
by magnetic fields, a characteristic required in transforming carbon steel and about seventeen times slower than that of
electrical power through induction. For welding, this is not aluminum. To understand controlling heat input and interpass
the most important difference in the properties of the two temperatures is very important when welding all materials to
metals but it is one of many important differences between avoid costly repairs or rejects.
steel and aluminum. Both materials are now more widely used
than ever and there is a good possibility that a welder will need
to weld on both of these materials during his or her career.
Welding of aluminum is different than welding of steel and
it is important for the welder to understand the “weldability”
of both.

Just two examples to illustrate the difference in weldability
between the two metals, ferrous and nonferrous, are the
corrosion resistance and the thermal conductivity. We know
that aluminum, as opposed to steel, is more corrosion resistant,
resisting weathering through the thin layer of aluminum oxide
on the surface. This layer is formed in a matter of Pico seconds
after exposure of aluminum metal to the atmosphere, since
aluminum metal is very reactive with oxygen. (A picosecond
is 10 of a second. That is one trillionth -- or one millionth
−12
of one millionth of a second, or 0.000 000 000 001 seconds. teMperature ManageMent in Welding
A pico second is to one second as one second is to 31,700 Means Money gained or Money lost
years) Aluminum oxide is an electrical insulator, has a much
higher melting point than the aluminum itself and hence, in To learn about properties and uses of ferrous and nonferrous
welding aluminum, it is required that the welding arc breaks metals gives the Hobart Institute diploma student a unique
through this oxide film, and cleans the oxide. Cleaning of body of knowledge for their future careers. Decades ago,
the surface immediately before welding helps. This is one of HIWT created its Weldability of Ferrous and Nonferrous
several important differences between welding aluminum and Metals Course and made it part of the diploma programs in
welding steel. response to the ever-increasing requirements of industry and
to make HIWT students even more employable. Most of our
Another important difference is that aluminum has a high students appreciate this course and see the value in it for their
thermal conductivity and this characteristic is often used in future careers.
welding equipment and other electronic systems as a heat
sink. (A heat sink is a passive component that cools a device (Continued on page 5)

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