Cast versus Wrought aluminum alloy
Cast versus Wrought aluminum alloy
(OP)
I have a question about the phrase "cast 7075-T6 aluminum." Every reference I have refers to cast aluminums with designations "AXX.Y", while the wrought aluminum alloys use the 2XXX, 3XXX, etc. designations, with the 'dash' "T-some number" indicating a heat treatment. Does "cast 7075-T6 aluminum" mean an aluminum casting with similar material composition as 7075 with a T6 heat treat, or does it mean the casting has similar mechanical properties of 7075-T6, such as yield, UTS, elongation, etc. Or something else?





RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
7075 is a pretty weird alloy, and requires IIRC, some combination solution anneal, cold forming, heat treat and rapid quenching to achieve its properties. There is very little liklihood that a cast version of the alloy could even come close to obtaining the same UTS as properly forged and aged 7075-T6 wrought forms.
RE: Cast versus Wrought aluminum alloy
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Title: High Strength Aluminum Casting Technology: Squeeze Casting of 7075 Alloy.
Abstract: The objective of this investigation was to develop wrought 7075-T6 mechanical properties in a cast aluminum alloy component of net or near-net shape. ((there's more))
Sounds to me as if they are trying to create a cast aluminum with the same mechanical properties as 7075-T6. Is that a bad interpretation of what I see?
RE: Cast versus Wrought aluminum alloy
Since they are working with cylinders I am guessing that they are looking to save a ton of machining time.
This isn't a simple casting process that they are using. This may a high pressure slush casting.
It might be interesting to see what chemistry they are using.
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RE: Cast versus Wrought aluminum alloy
As EdStainless pointed out, you have the correct understanding of the process that was investigated. Since this is/was a research project, the investigators used the wrought alloy nomenclature for their casting alloy/process, especially since it is the wrought version of the alloy that they are intending to replace with a casting. If this were to become standardized, such as in an ASTM casting standard, then the alloy would likely be given a casting designation, e.g. 7xx-T6.
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
Are you sure you aren't looking at a custom-forged shape?
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
can you perform a quick macro test to observe the flow lines if any. Absence of flow line will suggest a casting possibly
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
Regarding forged vs cast - aluminum is typically sand-cast, and you would see the typical sand roughness in un-machined areas. Forgings are much smoother, and you can sometimes see the "flow" of the metal grains if you polish/etch. More what I was thinking, though, is to look at the part shape, and say to yourself "could I have made this from a forging", since the process is inherently more limited than casting in terms of coring. Irregardless, you should try and get ahold of copies of the drawings.
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
Though I've haven't seen any injection molded 7075 parts, I do know that some attempts to make same was attempted several years ago.
We used some pretty complex injection molded parts, mostly 356.
RE: Cast versus Wrought aluminum alloy
7075 solidifies over the range 635 to 477 oC, with lots of segregation between higher melting intermetallics and a low temperature eutectic. Ingot intermetallics (DC cast, ~16oC/sec) are (Fe,Cr)Al3, (Fe,Cr)3SiAl12, Mg2Si, Mg(Zn2,AlCu) and CrAl7. It cannot be completely homogenized by heat treatment – significant hot working is required to break up and distribute the intermetallics. Also, Fe does not diffuse to any significant extent in the Al matrix below 400 oC, and Mn and Cr only above 500-550 oC.
--- Refs: various Metals Handbooks (phase diagrams, metallography & non-ferrous alloys), Aluminum Vol. I (1967), and Aluminum: Technology, Application and Environment, 6th Edn. (1998).
To avoid the casting microstructural problems, alternative methods include powder metallurgy using rapidly solidified powder, and more recently, thixotropic casting (stir casting) and spray casting. Note that in the article referenced by prost above, squeeze casting didn't solve the segregation problem (nor would HIP).
A few interesting articles on 7075 production and microstructure:
“For 70 years, aluminium alloys have been the materials of choice for both military and commercial aircraft structures. The ingot metallurgy (IM) alloys of the 2000 (Al-Cu-Mg) and 7000 (Al-Zn-Mg-Cu) series used thus far show several disadvantages caused by the production process. Such problems are primarily coarse intermetallic constituent phases, coarse grains, and macrosegregation, resulting in low fracture toughness.”
Mechanical Properties of Spray Cast 7XXX Series Aluminium Alloys (2002)
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Properties Of 7075 Aluminium Alloy Extruded From Rapidly Solidified Flakes And Conventional Atomised Powder [abstract] (1984)
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'Effects of Dispersoid Particles on Toughness of High Strength 7000 Aluminum Alloys'
http:
“Q: Why is aluminum alloy 7075 not listed in AWS D1.2, Structural Welding Code - Aluminum?
A: Most aluminum alloys are weldable, but a fair number of them are not, including 7075 aluminum....However, 7075 should not be used for structural work.”
htt
[Of course, 7075 is weldable, but the results are often bad. Layers of liquid may form parallel to surface, along the rolling or extrusion direction.]
Thermal Stability of Rapidly Solidified Alloys of Aluminium with Transition Metals [1st page only] (2006) http://www.scientific.net/0-87849-408-1/389/
Finally, you can identify 7075 by its speckled olive coloration when hard anodized. And, the intermetallics, if not well broken up/dispersed/homogenized, will appear as blisters in the anodize.
RE: Cast versus Wrought aluminum alloy
One important note regarding coarse intermetallic phases in 7XXX alloys. Because of their detrimental effects, alloy 7075 has been replaced in many critical applications with 7475. 7475 has a modified chemical composition to reduce intermetallic particles and increase fracture toughness. Here is a comparison:
Alloy
7075 7475
---- ----
Fe 0.50 0.12
Mn 0.30 0.06
Si 0.40 0.10
Ti 0.20 0.06
For T651 temper:
KIc(MPa√m) 22 37
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cast versus Wrought aluminum alloy
RE: Cast versus Wrought aluminum alloy
But 7075 (known as 75S in the 1940's & 1950's) isn't a casting alloy & hence isn't in any casting standards. It is only usable as a wrought alloy. But, few people are really familiar with aluminum metallurgy. So, the vast maority were easily duped that the only use of 7075-T6 tubes is for uranium enrichment centrifuges (although proven unsuitable by testing in 2002 at Oak Ridge National Labs done at the request of the CIA). Actual connection of 7075 to WMDs: Material of construction for the B-29s that delivered the atomic bombs ending World War II.