Casting Aluminum Issues
Casting Aluminum Issues
(OP)
I'm working on a streetlight with some cast aluminum parts. The base connecting the pole to the foundation is cast and I've spec'd 771.0-T71 up to this point as it has the required fu=48 and fy=45 psi required by the calc's. But 771.0-T71 is only listed for sand casting so far as I've discovered, and if this thing goes into production, it will probably require a die casting process because of high production volume (>300,000) and tight tolerances in areas.
As an alternate to 771.0-T71, I've found casting aluminum 201.0-T6 listed on a couple of die casting foundry websites. 201 has the strength I need: fu=68 and fy=60 and an elong. at failure around 7% (important if it gets hit by a car).
Any advice on high strength, relatively ductile casting aluminum with acceptable machinability? And reasonable cost.
Thanks,
As an alternate to 771.0-T71, I've found casting aluminum 201.0-T6 listed on a couple of die casting foundry websites. 201 has the strength I need: fu=68 and fy=60 and an elong. at failure around 7% (important if it gets hit by a car).
Any advice on high strength, relatively ductile casting aluminum with acceptable machinability? And reasonable cost.
Thanks,





RE: Casting Aluminum Issues
Regards,
Cory
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RE: Casting Aluminum Issues
I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
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RE: Casting Aluminum Issues
RE: Casting Aluminum Issues
RE: Casting Aluminum Issues
RE: Casting Aluminum Issues
I don't think you will get > 300 000 castings per year of A357 with yield strength ≥ 45 ksi.
TVP,
Alcoa sold their automotive casting division to a private equity firm. Here is a news story:
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This included the Pressure-Counter Pressure process, but I don't think Vacural was included in this.
Regards,
Cory
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RE: Casting Aluminum Issues
RE: Casting Aluminum Issues
Permanent mold looks to have a limit of around 3,000 before 'redressing' is required, but a lifetime of about 20,000 castings. Also, I should have been more clear about the estimated 300,000 volume anticipated. That is the initial target range, but it may occur over say, 3 years.
357.0-T6 seems to have fu=52 ksi and fy=43 attainable with perm. mold casting, which is very close to the 771.0-T71 I was using initially. I have a least a shot at making that work with little change to the section modulus.
I only find 357 under perm mold casting, not die casting. Can 357 be die cast, or does the die cast process decrease fu and fy because of increased porosity from trapped gas? Also, all the alloys I find under die casting have fu and fy's that are way too low to work.
Question: if I spec 357 for now, is it reasonable to also spec perm mold casting when I know they're going to have to redress the mold or molds probably every two or four weeks? And that they will go through roughly 300,000/20,000 = 15 perm molds before they reach the 300,000 target? Is that reasonable?
Thanks again.
RE: Casting Aluminum Issues
RE: Casting Aluminum Issues
Yes, it is reasonable to expect that the molds will require some amount of maintenance and/or complete replacement up to something like 15 molds for a production quantity of 300,000 pieces. These types of molds are not nearly as complicated as high pressure die casting tools, so they are less costly to manufacture and to maintain. The lowest cost solution is likely to be a permanent mold (gravity die cast or low pressure die cast) casting out of alloy A356 or A356 that is subsequently heat treated to the T6 temper. Vacuum die casting would only be a viable option if you could reduce the yield strength requirement, but then the section modulus (thickness) would likely increase beyond the point where hpdc is optimal (< 3-5 mm).
RE: Casting Aluminum Issues
It looks like permanent mold is the only way to go. My only other question - now that I checked in the Aluminum Design Manual (that AASHTO references for streetlight design) is that there's no fy listed for 357.0-T6. Only an fu=45 ksi.
But there is 354.0-T62 listed with fu=50 and fy=42 for 'designated areas'- locations which I can specify that must meet those values. Any objections to 354? Corrosion resistance is good w/r to stress corrosion cracking and 'ok' for NaCl spray exposure(actually a 'C' rating on a scale of A-F; unprotected A and B ratings are considered ok for seacoast exposures). But the base will be painted.
Best,
RE: Casting Aluminum Issues