Corrosion in automotive exhaust components is one of the major problems due to which failures occur
even after a very short period of time. Corrosion in such systems can be divided into two types: (a) cold
end corrosion and (b) hot end corrosion. These different ends of the exhaust system corrode by
different mechanisms. For cold end, the key concern has been corrosion due to interactions of salt
solution from outside and acidic condensate from inside. Presently, the most commonly used materials
in the automotive exhaust system are stainless steels. These steels contain high amounts of chromium,
nickel, manganese, molybdenum, titanium and nitrogen. Due to increasing cost of nickel and some
other alloying elements, there is a big intention to replace stainless steels by other substitutes. The aim
behind this study is to find low cost alternatives having enough corrosion resistance to achieve a
reasonable life time.
This work focuses on evaluation of corrosion resistance of Zn-Al-Mg coatings (ZM), hot dip aluminized
coatings (HDA), electrolytic nickel coatings (EN) on medium carbon steel. Numerous corrosion
simulation tests have been performed to develop a complete ranking of these coatings. The detailed
surface characterization including morphology, phase composition, corrosion products was studied. In
the end, a detailed mechanism of corrosion is discussed for each case.
Keywords: Automotive, metal coatings, salt spray corrosion test, condensate corrosion test, SEM/EDS.