Drawn from the innards of the earth, raw aluminum ore was discovered in significant quantity in 1824. It then became reliably
used industrially by the turn of this century. Gradually, aluminum became part of automobile production. Why? Simply put:
Aluminum's lighter weight, when compared with steel, furthered its use.
But unfortunately, a large problem occurred when constructing and repairing aluminum car bodies. Because of oxygen contamination,
quality welding was difficult. As a result, nuts, bolts and other fasteners held the metal together. Though heli-arc welding
emerged in 1942, this new welding method didn't immediately come into widespread use.
By 1950, the aircraft industry spawned a new era of electric welding. The inert gas, or TIG, system emerged. This welding
technology furthered aluminum use in automobile production, thus opening the door for the development of MIG, plasma and other
new types of metal welding. Now, living in a time that realizes the need for lightweight, fuel-efficient vehicles, we are
beginning to see aluminum body panels taking up more space in body shop repair bays.
Like a Winged BirdI-CAR instructors agree that it's important to understand the properties of aluminum. Compared to steel, aluminum is much
lighter and is a better electrical conductor. It also conducts and transfers heat very well. Aluminum cannot be magnetized
because it contains no iron. But it is softer and more easily scratched and almost too easily sanded. Finally, this metal's
hard, thin oxide layer gives it natural corrosion resistance. 
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It's aluminum alloys that complicate the battle. Aluminum may contain copper, manganese, zinc or silicon to enhance certain
properties. For example, 2000-series aluminum uses copper as its main alloy to increase strength. This is sometimes used for
outer and inner panels on hoods and deck lids. The 3000-series aluminum parts mainly use manganese and has increased in strength
and formability. A 4000-series piece has a low melting temperature and is used as a welding material. The 5000-series aluminum
uses magnesium as its main alloy. This improves strength and retains corrosion resistance. Some 5000-series aluminum is made
into hoods, tailgates and sunroofs. It's also used for unibody structural panels and for welding electrode wire. Having both silicon and magnesium as its main alloying elements, 6000-series has improved in strength and formability. This
series often forms outer panels on hoods, outer and inner deck lids where character lines are pronounced. With some all-aluminum
vehicles, it may be used for other exterior panels. Finally, the 7000 aluminum series contains zinc. This alloy has high strength,
which is put to use in bumpers, bumper reinforcements and door intrusion beams.
A Fire Breather?Now, how does an aluminum dragon handle heat? There are non-heat treatable and heatable aluminums. Non-heat treatable aluminum
alloys include the 1000, 3000, 4000 and 5000 series. While these may harden by working, they cannot be heat-strengthened.
If these become hardened when working on them, you can anneal them with heat. But take note that each temperature cycling
weakens the metal. If heated, cool the metal gradually. These parts are sometimes used for structural body parts and retain
excellent formability in weld areas.
The real fire breathers are the heat-treatable alloys. These include the 2000, 6000 and 7000 series. They are strengthened
by work hardening, however, and are annealed with heat. Some may even be strengthened by using heat. The heat-treatable alloys
have varying temperature limits. But if these limits are exceeded, they often lose strength in weld-affected areas.
The heat treatables should not be preheated before welding. It is also important to note that they may increase in strength
and brittleness during a paint bake cycle. The heat-treatable family may be as hard and strong as a dragon's scales-vying
with some steels. They are often used in exterior body panels, bumpers, bumper reinforcements and door intrusion beams.
Bouncing Off the Surface For basic metalworking, you will use most of the same tools you use to repair steel, but it is preferable to have a separate
set, as you won't want to contaminate your aluminum tools with steel particles that may contaminate aluminum surfaces. This
means cutting tools, sanding discs and pads, sandpaper and even shop towels used with steel body parts must be properly prepared
and cleaned before working on aluminum panels. You must also thoroughly clean metal-forming hammers, dollies and other tools
that are used for both metals. Avoid using use serrated, shrinking hammers. Remember: Aluminum is normally softer. With all tools, watch for gouging possibilities.
The faces and edges of metal hammers should be smooth and polished. Often, you may find it preferable to use wood, plastic
or leather hammers. Round off and smooth file edges to prevent gouging the aluminum surface.
To remove paint, do not use coarse grinding discs of less than 80 grit. Select open-coat discs and beware of clogged discs
that can overheat and smear a soft aluminum surface. When installing the disc, use foam backing pads. And definitely opt for
an orbital or dual-action sander, leaving your rotary grinder in the box.
If necessary, cut aluminum using a mechanical tool. Do not use an oxyacetylene or plasma torch. Follow the equipment and vehicle
makers' recommendations.
As with a steel part, make a good metal-working start by pushing and bumping with the appropriately contoured tool. Keep hammering
to a minimum because hammering stretches the softer metal faster than you are used to with steel. Bump and lift to a roughly
correct contour. Work until a springy resistance prevents metal movement.
Next, find any high spot and shrink the metal. Cold shrinking is nearly impossible on tempered aluminum. Heat shrink carefully,
keeping in mind that aluminum won't glow. Use heat crayons judiciously to control the heat you apply. With aluminum, forget
heating and water splashing. Don't use a shrink hammer. Shrinking aluminum is subtle. To shrink aluminum, choose a hammer
of the right size, shape and weight, or use a spoon or slapper and dolly. Next, use mechanical advantage. Some off-dolly straightening
as the simple leverage of working the low spot, used against a high one, shrinks the metal.
You can use a slapper to cover two high spots simultaneously. Cross-hatch the high spot with the low temperature indicator
crayon and set up an oxyacetylene torch with a soft, reducing flame. Work quickly and limit the temperature, working the heated
metal. Bump the high area down with the hammer or slapper while supporting the neighboring low area with the dolly. Work the
metal while it cools. The metal shrinks until it is cool to the touch. Use this heat and bump method until you restore the
proper shape. Practice and carefully observe the progress.
When the area's high spots are down and roughness remains, the next step is planishing. Using a hammer, roll the metal to
shape. Use off-dolly hammering to smooth the work. You can take planished aluminum to a high finish, even to a polish. Be
patient.
