Corrosion Behavior of Aluminized Steel Sheet under Exhaust Gas Condensate Environment in Automotive Muffler

Abstract

The followings are main results of investigation of corrosion behavior of aluminized steel sheet under exhaust gas condensate in automotive muffler.
(1) In neutral or weakly alkaline solution of NH₄ including Cl^-, NO₃^-, SO^2-₄, CO^2-₃, CH₃COO^- and HCOO^- which are found in exhaust gas condensate, corrosion of aluminized low carbon steel sheet is enhanced by galvanic corrosion between coating layer and base steel at the site of coating defect.
(2) Galvanic corrosion above is influenced substantially by the corrosion characteristic of coating layer and base steel. In the solution including Cl^-, SO^2-₄, CH₃COO^- or HCOO^- ion individually, corrosion of aluminized steel is accelerated by corrosion of base steel. Especially under Cl^- rich condition this phenomenon is remarkable. In the solution including CH₃COO^- or HCOO^- ion, corrosion is accelerated under lower pH corrosion condition which corresponds to ion dissociation at high temperature, but it is restrained by formation of passivation film on base steel in higher pH corrosion condition at room temperature.