Wednesday, 31 December 2008 13:38

Hey Toby 9 --- Everything You Need to Know to Repair Aluminum

Written by Toby Chess

Hey Toby – I am a technician in Los Angeles and I need some information on repairing an aluminum hood. Can you help me?

— Miguel from Los Angeles

Hey Miguel – Thanks for the question and yes, I can help you. First, I would strongly recommend taking I-CAR’s aluminum repair class — STA 01. This is an excellent class on the proper steps in repairing aluminum. I see many shops replacing a damaged aluminum hood that should be repaired.
    One problem is that most shops do not have the proper equipment and or the knowledge to affect an excellent repair. I recently conducted the STA 01 at Beverly Coachcraft in West Los Angeles. Dan Simkey arranged for me to conduct the class at his shop. Beverly Coachcraft is a Mercedes Certified Repair center and works on a large number of aluminum parts.

    His senior tech Juan had extensive aluminum training from Mercedes-Benz and feels very comfortable repairing aluminum. When I arrived at the shop, Juan was getting ready to weld a small crack on an M-B CL hood. I asked him if he had cleaned the hood properly to which he replied “yes.”
    I keep small little stainless steel brushes on my truck and, after retrieving one, I brushed over the area that he was going to weld and repair. To everyone’s surprise, it was still dirty. Bare aluminum when exposed to moisture and oxygen forms a chemical compound called aluminum oxide. This compound needs to be removed before welding because it changes the melting point of the aluminum.

    Note the black specs on the metal after brushing. My technique is to finish cleaning the area with acetone before welding or using aluminum pulling pins. You can also clean the area with a DA sander with 80-grit paper, but using low speeds. Let’s get back to the class.
    One of the requirements for repairing aluminum is that you use separate tools (one set for aluminum and another set for steel). The reason for the separate tools is the prevention of galvanic corrosion. When bare aluminum comes in contact with bare steel in the presence of an electrolyte, the aluminum will start to corrode.
    If you use steel tools on aluminum, any steel from the repair process will imbed itself into the soft aluminum and galvanic corrosion will occur. I use the aluminum repair station from Dent Fix when it holds my classes.

    The station has all the tools you will need to repair aluminum. Besides having the stud welder, the kit includes a vixen file, heat gun, hammers and dollies, and much, much more. To begin the process, the dent was sanded with P80 DA followed by a stainless steel brush and a final cleaning with acetone.
    A heat gun was used on the dent with a circular motion starting on the outside side and then moving in a slow spiral motion to the center of the hood. Heat was monitored by using a non-contact thermometer. If the temperature exceeds 570 degrees Fahrenheit, the aluminum will go through a process called annealing. Annealing will cause the aluminum to be permanently softened.

The next step is clean the area again (your hand will leave a residue on the clean aluminum).

Next the proper stud (you will have to know what series aluminum you are working with — available at the OEM web sites) is installed to the area that is still low.

The stud is pulled until the dent is flush with the rest of the part

If any spots are high, they will need to be taped down to create a smooth surface.

A vixen file and/or a DA with 80-grit sand paper are used as the final step before a coat of epoxy primer is applied. The final step is to apply body filler to the repaired area. It should be noted that body filler that is used is compatible with aluminum.
    I want you to realize that the repairs I outlined were just that, outlined. I strongly urge all repairers to take the I-CAR Aluminum Repair class. You can e-mail me at tcspeedster@yahoo.com if you would like to host a class at your shop. The course includes classroom presentation followed by “hands on” training — all this for one I-CAR Coupon.

Read 7510 times