Community Research and Development Information Service - CORDIS


Designs involving the use of lap joints are becoming increasingly common in the steel industry. However, pre-coated steel sheets assembled by lap joints are prone to suffer several corrosion processes: crevice corrosion, galvanic corrosion, etc. The literature reveals a lack of knowledge about the corrosion mechanisms and primary factors involved in this issue.

This study considers materials commonly employed in car manufacturing (electro-galvanised and galvanneal) and building (hot-dip galvanised and 55% Al-Zn, painted or not), which have been tested in the atmosphere and in the laboratory by means of electrochemical studies and accelerated corrosion tests.

The retention of moisture inside the lap between plates is the main cause of the premature deterioration of materials in this type of joint. However, the presence of oxygen is imperative for the development of corrosion processes in the lap joint. The attack morphology in the lap joint is usually preserved in the form of 'ripple-mark' waves.

Other factors, which do not alter the mechanism but do affect its amount and attack morphology, are material corrosion susceptibility and material surface condition. It has been seen that, below the paint film, differential aeration and differential contamination cells can reach driving forces of several hundreds of millivolts.

The study has shown that standard accelerated corrosion tests designed for free surface s are inadequate for correctly simulating the negative effects of lap joints. In the project, weekly cyclic tests have been designed to adequately simulate the behaviour of different materials in this type of joint. joint.

Additional information

Authors: MORCILLO M, CENIM, Madrid (ES);GONZALEZ J A, CENIM, Madrid (ES);ALMEIDA E, INETI, Lisboa (PT);PUENTE J M, Aceralia, Aviles (ES)
Bibliographic Reference: EUR 20067 EN (2002), pp.204. Euro: 31:00
Availability: EUR-OP Reference:KI-NA-20067-EN-S. Available from EUR-OP sales agents. URL:
ISBN: ISBN: 92-894-2146-0
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