Corrosion Effects on Fatigue Behavior of Zn-Cr+3 and Zn Flake Coated M8 DIN 933 Bolts

Abstract

In this study, fatigue behavior of Zn-Cr+3 and zinc flake coated bolts was investigated experimentally by considering corrosion effects. Fatigue tests were conducted on M8x50x1.25 8.8 DIN 933 bolts at normal and corroded conditions at force amplitudes between 2.35 and 5.36 kN at test frequency of 75 Hz. A part of bolts was subjected to salt atmosphere for corrosion. According to the Wöhler curves obtained from fatigue tests before corrosion, zinc flake coated bolts showed 1.55 times higher fatigue life compared to Zn-Cr+3. After corrosion, fatigue tests showed that the fatigue life difference increased to 2.10 times for the zinc flake coating. Moreover, corrosion was found to be ineffective on crack initiation region. For both coatings and corrosion conditions, fatigue cracks were seen to initiate from the thread roots.

Prognosis methods of stress corrosion cracking under harsh environmental conditions

“…Research has shown that the stress intensity factor K 1 is a significant indicator characterizing the stress corrosion process in metals [ 33 ]. Corrosion cracking can typically cause ductile metal alloys subjected to high temperature and tensile stress to fail suddenly [ 34 ].…”

Characterisation of the galvanic protection of zinc flake coating by spectroelectrochemistry and industrial testing

“…It is ideal for components for which the standards require high demands on accuracy of fit without rework, like bolts and nuts. [ 1,9 ]…”