×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Alum. 6061 vs 7075

Alum. 6061 vs 7075

Alum. 6061 vs 7075

(OP)
We are currently manufacturing a part out of 6061. The part is very similar to a roller lifter for an automotive engine in shape, and how it must perform. The part is being stressed in compression and also slightly side loaded. There is also lash in the assembly to make up for heat. The part runs in gravety fed oil. It is also hard anodized with a teflon type coating over top of the anodize. We have not had any significant failers, but the customer is asking us to use 7075 instead. Would there be any drawbacks to using the 7075 material such as possibly being more brittle. My concern is the two ears that hold the roller bearing could fatigue and snap off.

RE: Alum. 6061 vs 7075

7075 is more expensive than 6061. In my opinion, this is a case of "if it ain't broke, don't fix it". Your stated low incidence of failure suggests that there is no inherent stress problem with the part. I would leave it alone unless the customer absolutely insists on the change.

RE: Alum. 6061 vs 7075

(OP)
The customer is really insisting on this and cost doesn't seem to be a deteriant. I just want to make sure we do not create a new problem.

RE: Alum. 6061 vs 7075

I agree with swall. IF your customer is insistent, then perform a small trial. 7075 will not perform worse than 6061 under your stated loading conditions. The only concerns I would have are related to manufacturing. Is the part crimped or otherwise deformed at room temperature as part of an assembly process? Is the part completely machined from bar, or is it finish machined from a formed/forged blank? 7075 has limited ductility at room temperature, especially in the T6 temper.

RE: Alum. 6061 vs 7075

(OP)
It is completly machined from bar. It is a T6 temper.

RE: Alum. 6061 vs 7075

One possible consideration is the susceptibility of T6 7075 to stress corrosion cracking under sustained tensile loads. I don't know what the service conditions are ,but it is one thing to consider.

RE: Alum. 6061 vs 7075

nolimitmfg

what is the customers rationale for wanting 7075?
I would make analysis of both materials, I would sort of throw it back onto their lap.
and ask for a letter or email to remove your self as not responsible if a problem should arise.

HTH
mfgenggear

RE: Alum. 6061 vs 7075

(OP)
The customer's thought was, that the ears holding the roller axle were possibly mushrooming or pounding out over time, but there was no real evidence. If any did occur, it was because the bore was slightly undersize, causing the lifter pieces to stick. So we had to adjust the machined tolerance for the bore deviations.

The part is in service for about 9hrs a year. I would say it should run for about 2-3 years before needing possible replacement. The part is returned by a spring with any where from 150-1000 ft lbs. It is making 243 cycles up and down in about 13 seconds. A total of 9750 cycles over the course of a year. So there is sort of a pounding going on.

So will the compression, then non compression of the part cause stress cracking quicker than the current 6061 material vs 7075. The 7075 I believe will resist the mushrooming effect, but will it have a greater chance of stress chacking?

RE: Alum. 6061 vs 7075

nolimit

I uploaded the material data sheets for each material & compared the physical properties.
the 7075 was more impressive. however I would go the expert material engineers.
as stated above do an actual test.
I am an amature material engineer, i am not an expert. but these are my thoughts
I do see there is 1.5 x difference in hardness, the elongation is basicly the same. fracture toughness is equal.
if the customer wants the better wear & structural I would give it to them.

HTH
Mfgenggear

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources