In some instances a spring is required to operate in a corrosive environment which means some form of surface protection is needed. The options of protection available will depend on the application of the spring. If cost is an issue, or where the material needs to be of a required strength, than it may not be possible to design a spring with materials that will not corrode.
An obvious choice is the use of nickel alloys, they are excellent for corrosion resistance, however the cost can be prohibitive. A simple method is to simply oil or grease the springs, this should give a sufficient level of corrosion protection for springs in transit or when in storage (as long as the storage conditions are not too testing). Another effective method of protecting springs from corrosion is through either plastic coating or painting. The only issue with using either of these methods is that the protection is only effective until it is damaged, it will then be liable to corrosion underneath the finish. The easiest option is to manufacture the spring from carbon steel, wire drawn with a galvanised coating which should be sufficient enough in most circumstances, if not, a better protection is required. A popular method is to use a metallic finish which can be obtained by electroplating the spring. In order to ensure the maximum corrosion resistance it’s vital to use the correct electroplated metal. Zinc plate and cadmium (rarely used due to its toxicity) corrode in preference to steel and will protect the surface even when the coating is damaged. Nickel, copper and chromium plate will lead to the steel corroding when damaged so is not recommended. Nickel plate is only recommend when the component needs to undergo soldering and so it’s widely used in the electronics industry. There is a risk of hydrogen embrittlement when electroplating which can lead to component failure when it’s loaded. A de-embrittlement process must be carried out in order to minimise the risk, this process involves the component being held at an elevated temperature of 190-200°C for up to 24 hours to allow the hydrogen to dissipate. If low alloy spring steels such as BS2083 685A55 are to be used then they should not be electroplated under any circumstances due to the high risk of hydrogen embrittlement. In contrast, a mechanical zinc or zinc alloy plate will provide zero risk of hydrogen embrittlement and an equally effective corrosion resistance, all be it costly. The other options available include coating the spring with a resin impregnated with zinc flakes, they can have either a black or silver finish. They provide a superior protection to mechanical or electroplating and avoid the risks associated with hydrogen embrittlement.