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Influence of plasma electrolytic oxidation on fatigue behaviour of ZK60A-T5 magnesium alloy

Authors :
Alessandro Morri
Alessandro Bernardi
Carla Martini
Lorella Ceschini
Morri A.
Ceschini L.
Martini C.
Bernardi A.
Source :
Coatings, Volume 10, Issue 12, Coatings, Vol 10, Iss 1180, p 1180 (2020)
Publication Year :
2020

Abstract

Magnesium alloys are used in the motorsport and aerospace fields because of their high specific strength. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating, are necessary when they are used in humid or corrosive environments. The present study aimed at evaluating the effect of plasma electrolytic oxidation (PEO), followed by the deposition of a polymeric layer by powder coating, on the rotating bending fatigue behaviour of the wrought magnesium alloy ZK60A-T5. The specimens were extracted from forged wheels of racing motorbikes and were PEO treated and powder coated. Microstructural characterization was carried out by optical (OM) and scanning electron microscopy (SEM) to analyse both the bulk material and the multilayer, consisting of the anodic oxide interlayer with the powder coating top layer (about 40 &micro<br />m total thickness). Rotating bending fatigue tests were carried out to obtain the S&ndash<br />N curve of PEO-treated specimens. The results of the rotating bending tests evidenced fatigue strength equal to 104 MPa at 106 cycles and 90 MPa at 107 cycles. The results of the investigation pointed out that PEO led to a reduction in fatigue strength between 14% and 17% in comparison to the untreated alloy. Fracture surface analyses of the fatigue specimens, carried out by SEM and by 3D digital microscopy, highlighted multiple crack initiation sites at the interface between the PEO layer and substrate, induced by the concurrent effects of coating defects, local tensile stresses in the substrate, and increased roughness at the substrate&ndash<br />coating interface.

Details

Language :
English
Database :
OpenAIRE
Journal :
Coatings, Volume 10, Issue 12, Coatings, Vol 10, Iss 1180, p 1180 (2020)
Accession number :
edsair.doi.dedup.....1d0eedff8ba4af5747a99b59f6d0eb64