Ford salt spray booth
In this corrosion salt spray booth at Ford’s Arizona Proving Ground, a five-percent salt solution is applied to the top, sides and bottom of a vehicle.

by Tony Whitney

For motorists in years gone by – and for some of us old enough to look back on several decades of driving – rust was a constant problem. Even the best of automobiles was inclined to rust sooner or later – and usually sooner. Good old paint was the only method of protecting bodywork against corrosion.

Even in the late 1970s, I can remember buying a new Italian car then quite popular in Canada and detecting rust within a year of ownership – and it was bubbling through the roof from the inside! Even cars from Japan were prone to rust in their early years on this continent.

Recent years have seen remarkable changes in the way automakers rustproof their vehicles – and I don’t mean by building them out of composites or aluminum. Any well-looked-after vehicle will take many years for even a small amount of corrosion to reveal itself – even in areas of the country where winter road salt is present.

At one time it was dealers who took care of rustproofing vehicles. All kinds of fascinating systems – some still available for those who want to be doubly sure – were used to delay the onset of rust on a new car. Automakers began to take on the job of ensuring that cars would have a rust free life back in the late 1980s. According to Ford Motor Company, rust is now “a non-issue” with modern vehicles.

One of the first major automotive corrosion protection innovations was a paint layer called “anodic electrocoat” introduced back in the 1960s. Application involved applying an electrically charged coating to the unpainted vehicle body in a large tank. In the late 1970s, automakers began using cathodic electrocoat and Ford was among the first to make the switch. All Ford’s North American assembly operations were converted to electrocoat by the mid-1980s and one of the reasons for this was to reduce the environmental impact of materials containing lead. This process worked well for many years, but during the 1990s, many of them started looking towards galvanizing to make vehicles ever more corrosion-resistant.

Galvanizing is a process that can be applied to mild steel (as used to make most car bodies), cast iron or steel alloys. The body component to be galvanized is thoroughly cleaned and then dipped in a tank of liquid zinc at 500-degrees Celsius. The process coats the body panel or fabricated assembly of panels with a layer of highly corrosion-resistant zinc. Body panels can also be stamped into shape from sheet stock which has been pre-coated with zinc on one or both sides.

This process makes for a very rust-resistant body component indeed. Just think of all those galvanized steel silos you see on farms these days, standing out year round in all weathers and still staying shiny and serviceable for years. Of course, vehicle bodies are painted on top of the galvanized surface, so protection is even greater and the paint itself is usually topped by a clearcoat.

To make sure everything goes well when prepping a car body for life in the real world, Ford uses something called “digital pre-assembly.” Early on in the vehicle’s computer-aided design process, Ford makes a careful study of just where corrosion is likely to occur and where road salt is like to do its worst. Initially, automakers like Ford were galvanizing only panels where the damage was likely to be done, but nowadays, many automakers galvanize the entire vehicle.

Among Ford’s corrosion protection steps is the use of computer-aided engineering tools to develop and tune the large ovens and cure the electrocoat. It’s not just those outer body panels that benefit from this coating technology. Automakers protect their vehicles extensively against paint damage from stones, gravel and other road hazards. Polyurathanes and polyvinyl chloride coatings are used underneath the vehicle and also on rocker panels and lower body areas. If you check out your new car carefully, you’ll find that the lower side panels have a “bumpy” surface which is slightly soft – at least, you can often mark it with a fingernail.

Like other manufacturers, Ford puts evaluation vehicles through some of the most corrosive tests imaginable. Interestingly, salt spray tests are carried out at a Ford proving ground in Arizona rather than up north because there isn’t a corrosion threat below freezing level. Ford says that the worst thing you can do to your vehicle on a freezing night is park it in a warm garage where ice turns to water and gets into all the nooks and crannies. Of course, the kind of protection Ford and other makers have developed takes care of this hazard anyway, but an older car is a different story.

We’re reaching a time when rust on our vehicles is something we don’t think too about much any more. But it took many decades of research and testing to reach this point.

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