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The why and how of aluminum repair procedures

Friday, September 1, 2017 - 06:00
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Aluminum is continuing to evolve as a material of choice in OEM car design. Much of the increased use of aluminum is due to the need to meet government-mandated emissions requirements and for fuel economy. There are several reasons why aluminum is becoming popular as an OEM substrate.

Aluminum is a lightweight material that offers a cost-effective method for increasing performance, boosting fuel economy and reducing emissions in vehicles. Technological advances in manufacturing have made it easier to work with aluminum, compared to 20 years ago. Aluminum manufacturing is also escalating, helping to bring costs down and removing aluminum’s once “exotic” classification. It is now a more mainstream substrate and is being used, alongside plastics and high-strength steels, in vehicle manufacturing.

When structural cross bonding two dissimilar metals with rivets, the adhesive protects against galvanic corrosion that can occur between aluminum and steel

Aluminum evolution

When Ford Motor Company introduced its aluminum-bodied F-150 pickup truck in 2014, the auto industry underwent an evolution. No longer was aluminum a substrate used solely in high-end vehicles. Aluminum was perceived as a safe, viable alternative to traditional all-steel vehicles. The Ford F-150 models offered reduced weight for fuel efficiency, along with improved acceleration, braking and handling. It weighed up to 700-pounds less than previous all-steel models.

Building on its success with the F-150, Ford’s 2017 Super Duty® truck features an all-new high-strength, military-grade aluminum alloy body on an all-new, fully-boxed frame of over 95-percent, high-strength steel. The Super-Duty truck is up to 350 pounds lighter. Converting to the aluminum alloy in the body design allowed Ford to realize the weight savings.

How then is the evolution of aluminum in body design affecting collision repair shops? Basically, any changes that auto repair technicians must make to accommodate the repair of aluminum vehicles is really no different than how collision repair shops have adapted to other changes in the industry. The key to working with aluminum is to understand the differences and get the training needed to make the proper repairs.

It’s just metal, it’s just aluminum and it’s just a little different to work with – but once you have learned how to work with aluminum, it will be just as “easy” as working with steel and plastic substrates. If you roll back the clock to the late 60s when plastics were first used in vehicles, the industry faced the same challenges. Technicians did not know how to fix plastics, so it was a learning curve while the collision repair industry became more familiar with their use. The same evolution is taking place in the industry now with the increased use of aluminum.

OEM Evolution

Although there has been an expected focus on the particular products and procedures to use when repairing aluminum vehicles, it should be noted that changes in the collision repair industry are not due just to the use of more aluminum. There has been a shift in the repair information distribution route from the OEMs over the past several years.

Vehicle systems have become much more complicated, especially with the introduction of electronics, such as restraint systems, stability control devices and lane departure systems. It’s becoming more imperative for a repair technician to have the training needed to repair these more sophisticated vehicles. Changes in vehicle design happen much more quickly than in previous years, with new designs being introduced from year-to-year, even within the same models.

A technician must focus on the proper way to go forward to repair each particular vehicle. Especially with aluminum vehicles, it is important to know the specific grade of aluminum used in a hood, panel or component. Many autos have aluminum hoods, but all aluminums are not created equally. That is why it is crucial to check with the OEM to understand what type of aluminum is involved and how to properly perform a repair procedure for a specific vehicle.

Crash-durable adhesives ensure that structural parts such as these frame rails properly absorb energy.

OEMs, therefore, are becoming more involved in disseminating repair information to collision repair shops. The OEMs have a vested interest in making sure that their vehicles are repaired properly and returned to “like new” condition. OEMs are also realizing that the repair parts channel can be a profit center, and subsequently, they are recommending the use of OEM-approved replacement parts and products.

Collision repair evolution

At the OEM level, there is more of an effort being made to ensure that the process to repair a vehicle is identified and defined. To that end, many OEMs are recommending certain products be used to repair a vehicle. For aluminum repair, it’s not that the products are different from the ones used on steel-bodied vehicles, but it’s important to use the OEM-recommended products or an equivalent.

Products that are recommended for aftermarket use usually come about after they have been adopted by an OEM. For instance, several years ago, when crash-durable or impact-durable products were introduced to and used by the OEMs, they then began recommending them for repair operations. They wanted the same bonding and sealing products to be used for repair as were used in the manufacture of the vehicle.

Aluminum Alloy Grades

More than 60 years ago, the Aluminum Association established the wrought alloy designation system through its Technical Committee on Product Standards (TCPS), which was adopted in the U.S. in 1954. When the current system was originally developed, the list included 75 unique chemical compositions. Today, there are more than 530 registered active compositions and that number continues to grow.

What is an Aluminum Alloy?
An aluminum alloy is a chemical composition where other elements are added to pure aluminum in order to enhance its properties, primarily to increase its strength. These other elements include iron, silicon, copper, magnesium, manganese and zinc at levels that combined may make up as much as 15 percent of the alloy by weight.  Alloys are assigned a four-digit number, in which the first digit identifies a general class, or series, characterized by its main alloying elements. 

Commercially Pure Aluminum
1xxx Series

The 1xxx series alloys are comprised of aluminum 99 percent or higher purity. This series has excellent corrosion resistance, excellent workability, as well as high thermal and electrical conductivity.

Heat-Treatable Alloys
Some alloys are strengthened by solution heat-treating and then quenching, or rapid cooling. Heat treating takes the solid, alloyed metal and heats it to a specific point. The alloy elements, called solute, are homogeneously distributed with the aluminum putting them in a solid solution. The metal is subsequently quenched, or rapidly cooled, which freezes the solute atoms in place. The solute atoms consequently combine into a finely distributed precipitate. This occurs at room temperature which is called natural aging or in a low temperature furnace operation which is called artificial aging.

2xxx Series
In the 2xxx series, copper is used as the principle alloying element and can be strengthened significantly through solution heat-treating. These alloys possess a good combination of high strength and toughness, but do not have the levels of atmospheric corrosion resistance as many other aluminum alloys. Therefore, these alloys are usually painted or clad for such exposures. They’re generally clad with a high-purity alloy or a 6xxx series alloy to greatly resist corrosion.

6xxx Series
The 6xxx series are versatile, heat treatable, highly formable, weldable and have moderately high strength coupled with excellent corrosion resistance.  Alloys in this series contain silicon and magnesium in order to form magnesium silicide within the alloy.  

7xxx Series
Zinc is the primary alloying agent for this series, and when magnesium is added in a smaller amount, the result is a heat-treatable, very high strength alloy. Other elements such as copper and chromium may also be added in small quantities.  

Non Heat-Treatable Alloys
Non-heat treated alloys are strengthened through cold-working. Cold working occurs during rolling or forging methods and is the action of “working” the metal to make it stronger. For example, when rolling aluminum down to thinner gauges, it gets stronger. This is because cold working builds up dislocations and vacancies in the structure, which then inhibits the movement of atoms relative to each other. This increases the strength of the metal.  Alloying elements like magnesium intensify this effect, resulting in even higher strength.

3xxx Series
Manganese is the major alloying element in this series, often with smaller amounts of magnesium added. However, only a limited percentage of manganese can be effectively added to aluminum. 3003 is a popular alloy for general purpose because it has moderate strength and good workability and may be used in applications such as heat exchangers and cooking utensils.

4xxx Series
4xxx series alloys are combined with silicon, which can be added in sufficient quantities to lower the melting point of aluminum, without producing brittleness.  Because of this, the 4xxx series produces excellent welding wire and brazing alloys where a lower melting point is required. Alloy 4043 is one of the most widely used filler alloys for welding 6xxx series alloys for structural and automotive applications.

5xxx Series
Magnesium is the primary alloying agent in the 5xxx series and is one of the most effective and widely used alloying elements for aluminum. Alloys in this series possess moderate to high strength characteristics, as well as good weldability and resistance to corrosion in the marine environment. Because of this, aluminum-magnesium alloys are widely used in building and construction, storage tanks, pressure vessels and marine applications.

Many OEMs have been embracing the serviceability of the vehicle body for more than 30 years, and in that process, the choice of adhesives and sealants have become more important. Recently, when Ford built the F-150 truck, repairability was a key design element. Every aluminum replacement part for the F-150 comes with instructions, a parts list, repair diagrams, and a note about the tools and supplies needed to complete the repair.

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