Connector Contacts The Surface Of Atmospheric Corrosion

Atmospheric environment corrosion is one of the main reasons to cause electric contact failure of connectors. Atmospheric corrosion includes gas corrosion and dust corrosion. In foreign countries, the research on the effect of atmospheric corrosion on electric contact reliability is based upon long-term field exposure and lab accelerated corrosion, and flowing mixed gases (FMG) corrosion standard is established. Environment of China has particularity of severe gas pollution and corrosive dust particles. It is necessary and worth to carry through indoor air exposure of typical contact metal material, and to analyze characteristics and electric behavior of corrosion products. The results provide reasonable and believable reference to connector design and application.The thesis studies the physical property and electric performance of corrosion products formed on Au plating, Ni plating, Cu alloy sample and tin plating after long-term indoor air exposure. Corrosion products on Au plating show circular structure, rather than localized on pores. This special products structure increases contact failure probability. The circular corrosion products have strong compression strength, contact resistance under the condition of 1.0N normal force is still beyond the given failure resistance of 10mΩ. Its anti-wear performance depends on probe's curvature radius. Fretting number of corrosion ring is much more than that of corrosion core with small curvature radius, however, Fretting number of corrosion core is much more than that of corrosion ring with small curvature radius. Corrosion products formed on common metal behave dense and discrete corrosion spots, rather than whole corrosion film. It needs only several fretting number to get rid of the effect of corrosion particles formed on Ni plating and tin plating, and it takes more than one hundred fretting cycles to eliminate the effect of corrosion particles formed on Cu alloy sample.The thesis discusses and analyzes formation mechanism and growing process of corrosion products. Tidal corrosion mechanism is represented, which magnificently explains the formation of circular corrosion structure. However, it is incapable to simulate circular corrosion products structure with the combination of single gas accelerated corrosion and damp experiment. Using Weibull's probability distribution of reliability theory, reliable lifetime of Au plating in contaminated environment is calculated with only several months. The thesis also analyzes characteristics and contact behavior of corrosion products after single SO₂ gas accelerated simulation. Although the structure also shows discrete corrosion spot, and composition is single, corrosion products thickness is as high as tens micron. Corrosion products have stronger compression strength and shear strength. Static resistance is higher than tens ohms, and it needs several hundreds fretting cycles to get rid of corrosion products. Corrosion gas concentration affects composition and structure of corrosion products, and consequently affects its contact performance.The thesis verifies with experiment that dust particles in deed have corrosion property, and analyzes the effect of environmental parameter, including temperature and relative humidity, on dust corrosion. Dust corrosion is electrochemical reactive process, in which dissoluble salts are the internal cause, and environmental condition is the extrinsic factor. Dust corrosion degree increases with relative humidity, but there doesn't exist the critical humidity. A great number of dust particles deposits on sample surface during indoor exposure. Its density is much more than corrosion products density. Therefore, it can not ignore the effect of dust particles on contact performance. Dust particles shall incorporate in accelerated corrosion simulation. Atmospheric corrosion is the synergetic effect of gas corrosion and dust corrosion.The thesis discusses the effect of dust corrosion on electric contact behavior and the affecting condition. Dust corrosion products can trap dust particles and therefore increase the contact failure possibility.