Land Rover Discovery: Galvanic Corrosion

Galvanic corrosion is the cross-contamination of dissimilar metals, in this case aluminium and steel. Avoidance of galvanic corrosion is an important issue to be considered in the repair of aluminium bodied vehicles.

Precautions to prevent the contamination of exposed bare aluminium surfaces should be taken. Good housekeeping and cleanliness should be adopted throughout repairs and especially prior to welding, pre-treatment, (Pyrosil), and adhesive bonding.

The repair environment requires control and protection from dust and debris from conventional steel body repairs. All equipment must be clearly identified and used solely on aluminium.

Tools should be kept clean and in good order. Steel fastenings are coated to prevent galvanic corrosion. Fastenings should be examined during repairs and where damaged or suspect must be renewed.

The use of graphite, penetrating oil, or copper based anti-seize compounds upon the steel fixings is not recommended.

Where the original equipment surface protection (paint), is removed it must be repainted to the recommended standard.

Only Land Rover original bodywork components and Land Rover approved repair materials (sealer, paint etc.) are to be used for bodywork repairs.

GENERAL

The corrosion protection provided in production must be carefully maintained and/or reproduced during and after body repair work. It is only then that the long-term warranty against penetrative corrosion damage can be assured.

Land Rover Original Parts

All Land Rover bodywork components have a cathodic base coating.

Individual bodywork components are zinc plated on one or both sides (in different areas depending on vehicle model).

Together with elastic paint coating, this guarantees an optimum, highly resistant protection against corrosion caused by the impact of small objects such as gravel.

NOTE:

If possible, the individual protective layers (zinc, cathodic base coat) on Land Rover bodywork components must not be damaged or destroyed by sanding or other mechanical operations.

If hairline cracks at "bodywork connection areas" appear after reshaping work (e.g. at door hinges), it must be ensured that the corrosion protection provided in production is recreated. The complete paint covering must be re-created if necessary. The same applies to reshaping work on heavily profiled bodywork components (e.g. floor pan). Renew or touch-up the paint coating, sealing beads and underbody protection as necessary.

After repair, any interior surfaces which are no longer visible or accessible must be primed before cavity wax is applied. To be certain of an even coating on inner surfaces, careful application of spray (twice, with drying time in-between) must be carried out throughout the whole cavity.

If bodywork panels are strongly heated during repair work, this will invariably result in damage to or even destruction of the applied corrosion protection material. The effectiveness of the cavity protection material is reduced if heating occurs. Reworking of the affected areas is therefore vital.

Welded areas should be made good before corrosion protection is applied.

The corrosion protection measures to be taken when bodywork components are renewed are described on the following pages.

CORROSION PROTECTION OF NEW COMPONENTS

All new components must be inspected for transport or storage damage such as scratches or dents. The following operations may be necessary, depending on the extent of damage:

Undamaged New Component

• Do not grind the cathodic primer.
• Lightly sand using a Scotchbrite pad for paint preparation
• Thoroughly clean with silicone remover and rub dry.

Slightly Damaged New Component

• Sand out scratches.
• Finely sand the surrounding surface.
• Thoroughly clean with silicone remover and rub dry.
• Apply corrosion protection primer to bare areas.

Damaged New Components (bumps and dents)

• Beat out the dented area and sand down to bare metal.
• Apply polyester filler (only onto bare metal).
• Apply filler.
• Lightly sand the whole component.
• Thoroughly clean with silicone remover and rub dry.
• Apply corrosion protection primer to bare areas.

The clinched flanges on the hood, doors, tailgate and liftgate must be sealed with clinched flange sealer, if this is not already applied.

WELD COMPONENTS

Use a stripping disc to remove the cathodic primer on the inside and outside of the area to be welded. The stripped area should be kept as small as possible, retaining as much of the cathodic primer as possible, taking care not to damage the zinc coating.

Apply Welding Primer

NOTE:

The welding zinc primer must be stirred well or shaken before application.

Clean the repair area thoroughly (silicone remover).

Apply welding primer evenly to all weld flanges (old and new components).

NOTE:

The welding primer must be allowed to dry before welding is carried out.

All weld beads must be ground down after all welding is completed, taking care not to weaken the welded joint.

Any unevenness at the joint must be made good.

If necessary, spot weld missing weld studs into position.

The vehicle must be completely cleaned of sanding dust and metal swarf to reduce the risk of corrosion.

Clean and prime all internal areas and those to be sealed.

NOTE:

The primer must be dry before sealing mastic or underbody protection is applied. Do not use thinners when applying sealing mastic (thinners may remove cathodic primers and mastic will not dry).

Body Repairs - Corrosion ProtectionPartial Renewal

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