Working with Aluminum

Jan. 1, 2020
Like it or not, aluminum is here. Aluminum use in vehicle production has steadily increased during the last several years. Aluminum is quite frequently being used for exterior body panels and is making its way into the structural role of vehicles. Ar

Story and Photos provided by I-CAR

Like it or not, aluminum is here. Aluminum use in vehicle production has steadily increased during the last several years. Aluminum is quite frequently being used for exterior body panels and is making its way into the structural role of vehicles. Are your technicians ready to repair aluminum when it shows up in your facility? With the proper training, aluminum repairs can be less intimidating than you may think.

Aluminum serves many purposes in vehicle manufacturing. The two primary reasons vehicle makers use aluminum are to reduce weight and provide better handling characteristics. Aluminum also has great energy-absorbing characteristics, meaning that vehicle makers can produce a lighter vehicle without compromising protection to the vehicle occupants during a collision. Aluminum deforms at a predictable rate, allowing engineers to better predict the outcome when it is deformed due to a collision. Knowing what to expect during repairs to aluminum is key to the success of repairing it.

Differences from steel

A collision repair technician must first understand that steel and aluminum have different characteristics. Aluminum, in the pure state, is a much softer metal than steel. Therefore, the aluminum used in the vehicle manufacturing process is generally alloyed with other elements to create a metal with the physical properties that are needed.

Aluminum alloys commonly used for vehicle production can be broken down into two groups, heat-treatable alloys and non-heat-treatable alloys. The heat-treatable alloys gain mechanical properties when thermally treated during the manufacturing process. In some cases, additional heat-treatment may occur during the bake cycle for the finish at the assembly plant. Other applications are heated following the forming process of aluminum. Non-heat-treatable alloys gain mechanical properties by the cold-forming process. Forming the aluminum into a shape strengthens it by compressing and stretching the molecules. This is known as work hardening. Steel work hardens as well but not to the point that aluminum does.

Aluminum has less memory than steel, meaning it will tend to stay in its existing shape. The aluminum molecules lock into place and are very difficult to unlock. Additional force, as well as the application of heat, may be required to straighten the aluminum structure compared to a steel structure.

Aluminum structural use

Aluminum, when used in a structural role, is generally one and one-half to two times thicker than steel when it is used in a similar role. In some instances, it can even be four times thicker. Although the aluminum is thicker, the weight of the aluminum can be as much as half the weight of steel. The thicker material can lead to challenges when attempting to straighten structural parts. Aluminum is prone to cracking when it is bent, and even more so when it is thicker. The application of heat will relax the compressed molecules while pulling pressure is applied. This will aid in the molecules being returned to the shape and state they were in before the damage. It will also reduce the potential of the aluminum cracking when it is straightened to its original shape. Regardless of whether the aluminum is a heat-treatable or a non-heat-treatable alloy, heat can be applied during the straightening process. There are several other considerations when heating aluminum, which will be discussed later.

Structural aluminum parts generally come in the following categories: stampings, extrusions and castings. These parts are attached using a variety of methods at the assembly plant to create the vehicle structure. Depending on the design, these methods can be rivet-bonding (using rivets in conjunction with adhesives), riveting, gas metal arc welding (GMAW) or metal inert gas (MIG) welding, or laser welding.

Squeeze-type resistance spot welding (STRSW) is also used, but due to the high power demands for welding aluminum using this method, it is not as widely used as an attachment process. The attachment method of the aluminum structure will be an important consideration when straightening is attempted. The concern comes from welds or other attachment methods from cracking or tearing when pressure is applied.

Repair versus replace

Now that we understand some of the principles of an aluminum vehicle, let’s see what can be straightened. There is no general rule for repair versus replace on aluminum vehicles like the kink versus bend rule for steel structural repairs. In most cases, damaged structural aluminum will be straightened to repair indirect damage and the parts with visual deformation will be replaced.

Stampings and extrusions offer the most repair options. Castings will generally crack when bent and usually require replacement when damaged. As a general rule, if the part is cracked, either as a result of the collision or during the straightening process, it must be replaced. In most cases, the straightening of aluminum structural parts will be to remove the indirect damage and to restore the dimensions within tolerance. If visual deformation cannot be removed, the part will generally require either partial or complete replacement.

Another item we need to look at is what the vehicle maker says about structural straightening. Some vehicle makers are very strong on their stand of not allowing straightening to an aluminum structure. So strong, in fact, that they have published information warning against it. Regardless, the vehicle will usually require a trip to the frame rack for replacement of damaged parts. Other vehicle makers recommend only minor straightening, while others say straightening is acceptable as long as any areas of visible deformation are repaired. Those vehicle makers that say straightening may be attempted generally may have recommendations for anchoring and heating as well. There are also some vehicle makers who have restrictions on part availability and equipment that is required to repair the vehicle. The concern is the repair technicians need to be trained in the proper repair techniques required to restore the vehicle to its pre-damaged condition. Before attempting structural repairs to an aluminum-intensive vehicle, be sure to locate the collision repair information provided by the vehicle maker. Attempting to repair an aluminum vehicle without it could lead to some serious problems.

Anchoring

The first step when structurally straightening an aluminum-intensive vehicle is anchoring the vehicle to the frame rack. Some vehicle makers have specialty fixtures that will be required to secure the vehicle to the rack to prevent additional damage during the pulling process. Frame repair equipment providers may have clamps available for aluminum vehicles.

Due to the fact that aluminum will tend to stay in its existing shape, a greater amount of force may be required to straighten the vehicle structure when compared with a steel structure. The added amount of force makes anchoring that much more important. Improperly anchoring the vehicle can cause extensive damage to the vehicle structure due to the anchors tearing out. Inspection of the anchoring points during the straightening process is a requirement whenever pulling is being performed. This is especially important on an aluminum-intensive vehicle.

Heating during straightening

Now that the vehicle is on the frame rack, the vehicle can be measured and a repair plan can be developed. Here is where the heating comes into play. When pressure is applied, heat will help the aluminum become temporarily more elastic, allowing it to more easily return to the original shape without cracking or tearing. Before heat is applied, there are a few characteristics of aluminum that must be pointed out. Aluminum will not change color when it reaches the melting point, as steel does. Also, heat travels much quicker on aluminum than it does with steel.

It is crucial that the temperature be monitored when heat is applied to aluminum. There are several ways to do this, but the most likely choices are thermal indicating paints or crayons or using a noncontact thermometer. Noncontact thermometers read the temperature that the part is emitting, known as emissivity, not the surface temperature. If the part is shiny, reflections can make the reading inaccurate. To effectively measure temperature and to receive accurate readings, the coating of the aluminum must be intact. Some noncontact thermometers have an emissivity adjustment that can help the readings become more accurate, but the best method to get an accurate reading is to keep the coating intact or apply a coating to it. An aerosol primer is an effective coating that can be applied to any bare or shiny aluminum to make the noncontact thermometer read accurately.

When straightening aluminum, there are some temperature ranges that can be very effective. The general repair temperature guidelines are to heat the aluminum to a temperature range of 200-300°C or 400-570°F. Exceeding this range can approach the annealing temperature, which could compromise the strength of the metal. Also consider the effect of heat being applied and how it will travel into surrounding areas of the vehicle. This is of significant concern when dealing with rivet-bonded parts. Heat can travel to the adhesive and compromise its strength.

Following the repair plan

After developing the repair plan, straightening can be approached following the same techniques used to repair a steel structured vehicle except for one key factor. The areas that are dimensionally correct must be held in the position to prevent pulling the vehicle in the wrong location. Additional anchoring or blocking may be required to do this. Otherwise, the repair techniques are the same. After straightening, a dye penetrant test should be used to inspect the repaired areas for any cracking of the parts or the welds that may have occurred.

Planning and preparation

The fact is, aluminum has arrived in the vehicle manufacturing process. If you have not yet had the opportunity to repair an aluminum-intensive vehicle, chances are you will in the future. Having the knowledge and skills required for repairing aluminum before it shows up in your facility can help you be prepared when it does.

There are several I-CAR Enhanced Delivery Programs dedicated to informing all segments of the collision industry of the repairs to aluminum. Visit www.i-car.com and conduct a class schedule search to see what is available in your location. Also, be sure to locate the collision repair procedures from the vehicle maker before attempting structural repairs.

Sponsored Recommendations

Best Body Shop and the 360-Degree-Concept

Spanesi ‘360-Degree-Concept’ Enables Kansas Body Shop to Complete High-Quality Repairs

ADAS Applications: What They Are & What They Do

Learn how ADAS utilizes sensors such as radar, sonar, lidar and cameras to perceive the world around the vehicle, and either provide critical information to the driver or take...

Banking on Bigger Profits with a Heavy-Duty Truck Paint Booth

The addition of a heavy-duty paint booth for oversized trucks & vehicles can open the door to new or expanded service opportunities.

Boosting Your Shop's Bottom Line with an Extended Height Paint Booths

Discover how the investment in an extended-height paint booth is a game-changer for most collision shops with this Free Guide.