Influence of microarc oxidation and hard anodizing on plain fatigue and fretting fatigue behaviour of Al-Mg-Si alloy

The present study compares the performance of microarc oxidation (MAO) and hard anodizing (HA) treated Al-Mg-Si alloy (AA6063) test samples under cyclic loading in uniaxial tension with a stress ratio of 0.1 (plain fatigue) and fretting fatigue loading. Fatigue test specimens were treated using MAO and HA techniques. MAO coated specimens were ground to reduce the surface roughness comparable with that in HA coated specimens. In that process the porous outer layer was removed. Characterization of coated and uncoated specimens was done with reference to the coating morphology, microhardness, surface roughness and residual stress. The specimens were tested under plain fatigue and fretting fatigue loading at ambient temperature. While the ground MAO coating exhibited relatively less amount of porosity, HA coating had through thickness cracks. MAO coating had compressive residual stress and it was very hard compared with HA coating. Both types of coated samples exhibited slightly higher friction force than that experienced by the uncoated specimens. Fretted region of the HA coated samples was rougher than that of the MAO coated specimens. Plain fatigue lives of both coated samples were inferior to those of the uncoated specimens. The inferior plain fatigue lives of MAO coated specimens compared with those of the substrate may be attributed to the tensile residual stresses supposedly present in the substrate leading to an early crack initiation in the substrate adjacent to the coating. As friction force of MAO coated samples was higher than that experienced by uncoated specimens, the fretting fatigue lives of MAO coated samples were slightly inferior to those of uncoated samples. As the anodized layer had preexisting through thickness cracks and strong adhesion with the substrate, cracks propagated from HA coating through the interface into the substrate easily. This may be the reason for the HA coated samples exhibiting inferior plain fatigue and fretting fatigue lives compared with MAO coated and uncoated samples.

[1]  P. Dearnley,et al.  The sliding wear resistance and frictional characteristics of surface modified aluminium alloys under extreme pressure , 1999 .

[2]  K. Stokes,et al.  Corrosion, erosion and erosion–corrosion performance of plasma electrolytic oxidation (PEO) deposited Al2O3 coatings , 2005 .

[3]  Y. .. Wang,et al.  Microarc oxidation coatings formed on Ti6Al4V in Na2SiO3 system solution: Microstructure, mechanical and tribological properties , 2006 .

[4]  L. Rama Krishna,et al.  The tribological performance of ultra-hard ceramic composite coatings obtained through microarc oxidation , 2003 .

[5]  G. Sundararajan,et al.  Mechanisms underlying the formation of thick alumina coatings through the MAO coating technology , 2003 .

[6]  A. Matthews,et al.  Characterisation of oxide films produced by plasma electrolytic oxidation of a Ti–6Al–4V alloy , 2000 .

[7]  T. W. Clyne,et al.  Thermo-physical properties of plasma electrolytic oxide coatings on aluminium , 2005 .

[8]  W. Xue,et al.  Growth regularity of ceramic coatings formed by microarc oxidation on Al–Cu–Mg alloy , 2000 .

[9]  Yang-ming Chang,et al.  Residual stress measurement by X-ray diffraction , 1972 .

[10]  Aleksey Yerokhin,et al.  Fatigue properties of Keronite® coatings on a magnesium alloy , 2004 .

[11]  S. Gnedenkov,et al.  Composition and adhesion of protective coatings on aluminum , 2001 .

[12]  A. Matthews,et al.  Effect of combined shot-peening and PEO treatment on fatigue life of 2024 Al alloy , 2006 .

[13]  A. Matthews,et al.  Plasma electrolysis for surface engineering , 1999 .

[14]  S. Joshi,et al.  Effect of detonation gun sprayed Cu–Ni–In coating on plain fatigue and fretting fatigue behaviour of Al–Mg–Si alloy , 2006 .

[15]  A. Matthews,et al.  Thickness effects on the mechanical properties of micro-arc discharge oxide coatings on aluminium alloys , 1999 .

[16]  Kun Wu,et al.  Effects of microarc oxidation surface treatment on the mechanical properties of Mg alloy and Mg matrix composites , 2007 .

[17]  A. Matthews,et al.  Abrasive wear/corrosion properties and TEM analysis of Al2O3 coatings fabricated using plasma electrolysis , 2002 .

[18]  S. Xin,et al.  Composition and thermal properties of the coating containing mullite and alumina , 2006 .

[19]  R. Rateick,et al.  Effect of hard anodize thickness on the fatigue of AA6061 and C355 aluminium , 1996 .

[20]  G. Sundararajan,et al.  A comparative study of tribological behavior of microarc oxidation and hard-anodized coatings , 2006 .

[21]  Z. Luo,et al.  Structure and antiwear behavior of micro-arc oxidized coatings on aluminum alloy , 2002 .

[22]  R. Hermann,et al.  Film-assisted fatigue crack propagation in anodized aluminium alloys , 1995 .

[24]  Jin Zeng-sun,et al.  The effects of current density on the phase composition and microstructure properties of micro-arc oxidation coating , 2002 .

[25]  S. Lixin,et al.  Properties of aluminium oxide coating on aluminium alloy produced by micro-arc oxidation , 2005 .

[26]  T. Clyne,et al.  Porosity in plasma electrolytic oxide coatings , 2006 .

[27]  Yaming Wang,et al.  Fretting wear behaviour of microarc oxidation coatings formed on titanium alloy against steel in unlubrication and oil lubrication , 2006 .

[28]  A. Matthews,et al.  Residual stresses in plasma electrolytic oxidation coatings on Al alloy produced by pulsed unipolar current , 2005 .

[29]  A. Merati,et al.  Determination of fatigue related discontinuity state of 7000 series of aerospace aluminum alloys , 2007 .

[30]  S. Raman,et al.  Effect of shot blasting on plain fatigue and fretting fatigue behaviour of Al–Mg–Si alloy AA6061 , 2005 .