Corrosion protection for car parts and safety
Earlier this year NACE International released the International Measures of Prevention, Application and Economics of Corrosion Technology (IMPACT) study. It estimates that the global cost of corrosion is $ 2.5 trillion, roughly 3.4 % of global GDP.
The research also included a case study on corrosion management within the auto industry, and highlighted its successes. The study found that the automotive industry had made savings of $ 9.6 billion or 52 % annually in 1999 compared to 1975, adding that the success was because ‘corrosion prevention decisions were made at the highest level’.
Much progress has been made in the intervening years, but corrosion remains an expensive problem for the automotive industry, and recent recalls have only served to highlight the issue.
Recalls due to corrosion
The full cost of a recall is hard to quantify and varies on an individual basis. Repairs, legal cost and damage to brand image can all have a financial impact, which will depend very much on the defect that caused the recall, and the way it is dealt with.
Corrosion is a long-term problem for car manufacturers, not least because a number of factors - some of which are out of the control of OEMs - contribute to the issue. Crucial parts such as brake and suspension components can be susceptible to corrosion, and as these are critical to safety on the road, manufacturers and suppliers continue to develop sophisticated corrosion prevention technologies. A few recent recalls involving Mazda, Toyota, Kia and Mitsubishi serve to highlight the problem of corrosion on suspension parts.
In August 2016 Mazda confirmed that it was recalling more than 190,000 CX-7 crossovers from model years 2007-2012. The US National Highway Traffic Safety Administration confirmed that water could enter the CX-7’s front suspension ball joint fittings. If the water contains contaminants, such as salt used to de-ice roads, it could cause the ball joint to corrode. If the corrosion was severe enough it could in turn cause the front lower control arm to separate from the vehicle, making the car difficult to steer and increasing the risk of an accident.
Toyota initiated a similar recall this summer with more than 370,000 Toyota and Lexus vehicles being called back to fix a serious problem with the suspension. The vehicles concerned are the 2006-2011 RAV4 crossover and the 2010 Lexus HS 250h Sedan. The issue is that the lock nuts on the rear suspension arm may not have been properly tightened. As a result they could be too loose, allowing the thread to rust and the suspension arms to fail. Again, this would make the vehicle difficult to control and increase the risk of an accident.
Yet another recall came from Mitsubishi, with over 174,000 vehicles recalled due to potential corrosion of front lower control arms. Similar to the Kia issue, recalls are being made in states which use salt to de-ice roads. The corrosion caused could lead to the front lower control arm detaching from other suspension components, thus making the vehicle unsafe to drive. All recalled vehicles will be inspected, and additional anti-corrosion coatings will be applied to new and existing parts for future protection.
Recalls are part and parcel of a mass-production industry and, as mentioned, the auto industry has made great strides over previous decades. However, it is clear that corrosion is still an issue - particularly when salt combines with water to attack metal parts and components. The fact that different types of corrosion affect automobiles also means that various solutions are required.
Atmospheric corrosion can occur when any metal surface of a vehicle comes into contact with air containing moisture. A thin film of moisture deposited under nonzero humidity conditions is sufficient to cause the gradual decay of steel surfaces. The thickness of the film will depend upon factors such as ambient temperature and pressure, relative humidity, and the presence of salts.
Crevice corrosion refers to electrochemical processes that occur in confined spaces, such as gaskets, seals, flanges, and spaces filled with deposits. This type of corrosion is a localized attack due to the presence of a stagnant solution or an electrolyte.
Galvanic corrosion occurs when two different metals are placed in electrical contact. One metal can corrode preferentially in relation to the other. The corrosion of nuts and bolts to join components together is one such example.
Pitting is another form of localized attack, similar to crevice corrosion. It typically occurs in otherwise passive materials where the passive oxide film that protects the metal is broken down as a result of chemical or mechanical attack. The chlorine in salt water is very effective at breaking down such passive oxide films.
Corrosion Treatments and Solutions
Environmental conditions can play a significant role in corrosion, but the causes can also be traced back to manufacturing processes, and treatment is a sizable sector in its own right. The market size of anti-corrosion coatings was $ 22.45 billion in 2015, and is projected to reach $ 30.04 billion by 2021. A variety of solutions are in play within the industry, and some of the leading protective coatings are detailed below.
Automotive supplier Henkel provides a range of surface technologies to protect against corrosion, with services including pre-treatments, process control equipment, metal coatings, and surface car treatments with corrosion protection. Henkel’s solutions are optimized to work with a variety of applications and processes, from chassis to body-in-white.
The Bonderite (formerly Aquence) M-PP 937 coating for example delivers corrosion protection for applications such as vehicle frames and chassis components. The epoxy-acrylic urethane coating provides a high gloss appearance while maintaining high levels of performance on Neutral Salt Spray (NSS) testing and automotive OEM cyclic corrosion tests. The hard coating provides a number of benefits to manufacturers, including environmental sustainability with very low VOCs, heat stability, excellent flexibility and impact resistance, and lower maintenance requirements.
Autodeposition advantages, compared to conventional coating operations, include significantly less manpower and equipment, and less cycle time, energy, handling, packaging and transportation. It can be used in a combined cure sequence with some topcoats due to the low VOC content, and it is self-limiting so it cannot be over-applied. The coating also provides a uniform thickness on all parts, including edges and complex shapes, with no drips, runs or sags.
Henkel’s coating products are approved by the likes of BMW, Volkswagen and PSA.
Surface Technology is a leading supplier of automotive coatings and coating application services, numbering Jaguar Land Rover, BMW, Volkswagen and Toyota among its customers.
Its coating services include powder coating, dry film lubrication, zinc nickel, porosity sealing, zinc plating, and electroless nickel plating. Applications include engine blocks and cylinder heads, air conditioning components, power steering and brake pipes, fuel pipe and fuel delivery systems, and brake calipers. As well as anticorrosion properties, their coatings also provide wear resistance, anti-fretting, anti-galling, electrical insulation where required, and heat and sulfur corrosion resistance.
BASF is another key supplier which provides a wide range of coatings, paints, and processes specifically for automotive applications. Its e-coatings portfolio includes Cathoguard 800 and Cathoguard 900 - the latest technologies, which are both tin-free to meet regulations, and contain less than 1% solvents.
These cathodic e-coatings are applied during a dip in an electrocoat tank, and protect the car’s edges, surfaces and cavities from corrosion. To achieve cathodic e-coating, an electric current is used to apply the paint to body or component permanently. The part to be coated effectively becomes a cathode, with a negative charge. The coating’s binder particles act as cations, with a positive charge. In the cathodic e-coat bath, the coating particles migrate towards the steel body or part with the aid of an electric current, and are deposited. The process provides an ideal coating for corrosion protection, as all cavities and edges can be uniformly covered.
In such a high volume industry, recalls of one kind or another are inevitable. However, the cost is far from insignificant, and corrosion is one of the main reasons that recalls are initiated. The introduction of lightweight metals into manufacturing has also presented a number of new challenges, with metals such as magnesium useful for weight reduction but susceptible to corrosion. A variety of approaches are required to protect different materials and components against corrosion, and it is a sector of the automotive industry that will continue to develop.