A study of OY water test dedicated to internal corrosion of automotive heat exchangers using electro-chemical and statistical tools

摘要

Aluminium is the preferred material to produce brazing sheets for automotive heat exchangers. Given the wear resistance and durability requirements of next generation radiators, the combination of a sacrificial waterside cladding on a 3xxx alloy core should be optimised. The down-gauging trend is particularly critical with respect to mitigating pitting in order to prevent perforation. Although the experimental conditions are not sufficiently widely shared, the so-called OY water test is mostly practised as an accelerated corrosion test for inner side of radiators. The present work addresses the corrosion mechanisms and key parameters during a three-day immersion test in stagnant OY solution at 88℃. For that purpose, an in-situ electrochemical device has been implemented so that both sample corrosion potential and solution oxidizing power via a platinum electrode can be recorded. In addition, ZRA measurements have been performed to assess the corrosion kinetics while the test is in progress. Such a monitoring provides a mechanistic understanding of how the corrosion stages unfold during the three-day test as a function of cladding material or OY water composition. This could provide an electrochemical criterion to be used as a tool to help cladding material selection. Furthermore, reliable data is deduced from image analysis of the sample surface giving information on pit density and surface fraction affected by corrosion. A statistical analysis of maximum pit depth on each square centimetre section of the sample surface is also given as a cumulative distribution function.