Abstract
The effect of plasma electrolytic oxidation (PEO) on the fatigue of AZ61 magnesium alloy has been investigated under high cycle conditions in air and 3.5% NaCl solution. PEO employed an alkaline pyrophosphate–silicate–fluoride electrolyte, with an offset square waveform, a frequency of 50Hz, and current density of 130mAcm−2. The PEO treatment led to reductions in the fatigue limit by 38% in air and by 56% in 3.5% NaCl solution. The reduction of the fatigue limit is attributed to cracking of the coating, roughness of the alloy/coating interface, corrosion and influences of Al–Mn particles.
Highlights
Magnesium alloys are attractive for many applications because of their light weight compared with materials such as steels and aluminium alloys [1,2,3]
The present study investigates the effect of plasma electrolytic oxidation (PEO) on the fatigue behaviour of extruded AZ61 magnesium alloy in air of 33% relative humidity and in 3.5% NaCl aqueous solution
Three types of specimen were employed for PEO: (i) flat specimens, cut transverse to the extrusion direction, of 20 mm diameter and 2.5 mm thickness for examination of the coating; (ii) fatigue specimens with a gauge section of length 15 mm and diameter 7 mm (see Fig. 1(a)); (iii) cylindrical specimens of length 50 mm and diameter 7 mm for assessment of the uniformity of coatings on a curved surface similar to that of the fatigue specimens
Summary
Magnesium alloys are attractive for many applications because of their light weight compared with materials such as steels and aluminium alloys [1,2,3]. Electrochemical processes are able to produce relatively thick, protective coatings [11], with much recent attention being given to plasma electrolytic oxidation (PEO) [12,13]. Ceramic coatings produced by PEO can provide high wear resistance and corrosion protection, the latter especially when the coating forms part of a paint scheme [13,14]. They are usually formed in aqueous electrolytes at high voltages, with the coating material being produced at locations of short-lived discharges [15]. Fluoride ions may promote the formation of a protective barrier film [11,18], which can provide
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