A356 Yield Properties 2

[walkis15]

Wondering what others are getting for yield stresses on A356 - T6 aluminum castings. I'm seeing design callouts for up to 240MPa (34.8 ksi). Seems that designers are pushing the limits of the alloy possibly beyond capabilities. From excised bars, I see a wide range, but nothing to the level of confidence to agree to 240MPa as a min.

 

[israelkk]

According to MIL-HDBK-5J the minimum Ultimate tensile strength of A356-T6 conform to AMS-A-21180 is 38 ksi.

 

[walkis15]

Well, yes, I understand the 'standards', but I'm wondering what people are seeing in practice. And I'm talking yield, by the way, not ultimate.
I'm trying to design a suspension component, FEA shows peak stress just under 240MPa. I don't think this can be achieved with A356-T6. Can anyone shoot me some typical A356-T6 data, or even comment on the alloy, or suggest an alternative?

 

[swall]

You might consider 357 alloy, which is basically a jazzed 356. I'm showing (Aluminum Association Hdbk) 45ksi min uts for permanent mold cast. I've probably got more data, but it is in my other office at the moment.If 357 won't do it, you need to go to 201 alloy.

 

[unclesyd]

[ul]

38,000 UTS
27,000 YST 0.2%
5 Elg % 1/2" bar in 2" gage length
30,000 SStr Single shear from double shear tests
13,000 FS 500 million cycles of reversed stress
[/ul]

From an ALCOA Handbook.

We had thousands of parts made from 356 T-6 and other tempers and we found the published physical data to be a little on the generous side when compared to the real data gleaned from our actual components. Like the Elongation number 5%, we never measured over 3% with the end result being our designs assumed this. At the same time we found the UTS generally to be a measurable quantity higher than published values.

 

[israelkk]

When you say "peak stress" is it at a singular position or across an area? Did you analytically checked if it is logical to have such a peak stress at that point (FEA analysis can give false result if not carefully applied). Is your suspension see cyclic load or a static load?

 

[swall]

My experience mirrors that of unclesyd, at least with C355-T6. Mechanical properties from specimens machined from castings are lower than published values (which if you read the fine print, come from separately cast test bars).Some times, with a bar machined from a casting, we would be lucky to measure 1% elongation. BTW, some specs, such as AMS 4215, were written with different requirements for tensile specimens machined from castings.Also keep in mind that when specimens are machined from castings, you take them from where there is enough metal, not necessarily from the critical stress points.

 

[TVP]

What type of castings? Sand, permanent mold, squeeze cast? Delphi has published some good data on statistically significant properties for A356-T6 squeeze castings:

statistical min properties
207 MPA yield, 276 MPa ultimate, 70 fatigue at 10⁷ cycles

Weibull B1 capability
231 yield, 307 ultimate, 90 fatigue

average
259 yield, 329 ultimate, 103 fatigue

The typical HT parameters were solution at 1000F for 12 hours, quench as low as possible, then age at 310 F for 3-5 hours.

 

[walkis15]

Process is low pressure permanent mold. Thanks for the data, TVP, particularly the min data.
This is typical data I've seen. The key now is to determine the safe min value to sign up to. I prefer to express tensiles as mean - 3*sigma, but won't happen in this case. That's why I have to be more aware of the low flyers as a min spec.
Israelkk, the peak stress is over an area, not a point, and not an edge stress.
Swall, I am considering 357 or maybe 354. I think maybe I can get the properties with a higher Mg content.
Thanks everyone for your comments.