aluminium: anodization and fatigue resistance

[Meccbell]

6000 series aluminum (60606061-6082), pressed parts with internal pressure (210 bar) and subject to light bending (arrow equal to about 1/500 length) in alternating cycles (in one sense and another) with frequencies of about 5-8 cycles per minute:

Is it true that anodization decreases the fatigue resistance of the pieces made with these alloys?

I asked the question to 3 people that for the work they do they mean, or should be understood, of this matter and the answers were: Yes, no, maybe...

So I got there. .
Does anyone have experience or particular knowledge about this?

 

[zeffiro62]

I responded to you on mechanics and surroundings, anodising decreases fatigue resistance.
However, anodizing with chromic acid is less resistant to fatigue than anodising with the cheapest sulphuric acid and with more durable anodization but more aggressive and with more porous surface

 

[PierArg]

Hi.
I'm not on the subject, but I knew that anodising lowers the fatigue limit of a material.

I believe, in my opinion, it is because the treatment of anodization can lead to a phenomenon of "grain growth" and consequently the reduction of fatigue resistance.

 

[desMoira]

Hello mecc,
anodization can in fact reduce fatigue resistance on aluminum components, for a matter of intrinsic fragility of the treated layer in contrast to the increase of hardness and corrosion resistance for which it applies. In practice the surface layer is found to have mechanical characteristics different from those of the bulk, in particular it can be itself zone of nucleation of fatigue cracks.
the reduction of fatigue resistance is correlated not only to the type of anodization, so in fact that the chromic one is preferable (for the class 6000 usually uses sulphurics), but above all to the thickness of treatment. However, we are talking at the limit of a few %, and then also of the alloy and the state of supply.
a widespread solution to increase the fatigue resistance of the components to anodize at least x the class 2000 and 7000, is the pallination, essentially for the residual tensions of compression that induces on the substrate for plastic deformation (the non-nuclear and do not propagate in compressed zones).
hope this will be helpful.. .

 

[Fulvio Romano]

Hi.
I'm not on the subject, but I knew that anodising lowers the fatigue limit of a material.

aluminum has no limit of fatigue

Hello mecc,
anodization can in fact reduce fatigue resistance on aluminum components, for a matter of intrinsic fragility of the treated layer in contrast to the increase of hardness and corrosion resistance for which it applies. In practice the surface layer is found to have mechanical characteristics different from those of the bulk, in particular it can be itself zone of nucleation of fatigue cracks.
the reduction of fatigue resistance is correlated not only to the type of anodization, so in fact that the chromic one is preferable (for the class 6000 usually uses sulphurics), but above all to the thickness of treatment. However, we are talking at the limit of a few %, and then also of the alloy and the state of supply.
a widespread solution to increase the fatigue resistance of the components to anodize at least x the class 2000 and 7000, is the pallination, essentially for the residual tensions of compression that induces on the substrate for plastic deformation (the non-nuclear and do not propagate in compressed zones).
hope this will be helpful.. .

the ball, for the steels, increases the fatigue resistance, but palling a fragile surface like the anodized one, sure that no cracks are grafted? the fragile surface, being fragile, does not deform much plastically, so the compressed areas should be rather limited.

I mean nothing.

 

[bagaroz]

I press that I am a student, and what I carry has no practical validation. as we have been told the properties of aluminium alloys depend strongly on the state of supply (among other things subject to a revision of the norm in recent years).
As you have been noticed in particular you cannot define a limit of fatigue as for steels, the curves for such materials have a double knee. I do not know the temperature of the fluid flowing in the tube, in case it is high it also considers the fatigue cycles due to thermal expansion, especially for joints and welding

 

[PierArg]

aluminum has no limit of fatigue

I correct the caxxata, I meant resistance.

Thank you.

 

[desMoira]

aluminum has no limit of fatigue

the ball, for the steels, increases the fatigue resistance, but palling a fragile surface like the anodized one, sure that no cracks are grafted? the fragile surface, being fragile, does not deform much plastically, so the compressed areas should be rather limited.

I mean nothing.

hello fulvio, the ball for aluminum alloys is for components da anodizzare, in the sense that precedes the treatment of anodization.
is valid for all surface treatments of hardening/coating: the ball (when you choose to carry out it, i.e. for details subjected to fatigue) always happens before these. and, moreover, it must be calibrated according to the material, that is its mechanical characteristics... aluminum and steel ball parameters are quite different.

 

[Fulvio Romano]

hello fulvio, the ball for aluminum alloys is for components da anodizzare, in the sense that precedes the treatment of anodization.
is valid for all surface treatments of hardening/coating: the ball (when you choose to carry out it, i.e. for details subjected to fatigue) always happens before these. and, moreover, it must be calibrated according to the material, that is its mechanical characteristics... aluminum and steel ball parameters are quite different.

Here. Now I understand.. .