Corrosion Studies of Different Metal Coatings for Automotive Exhaust Applications

摘要

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-AI-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.