Given that a billet is a casting and that you say it’s the same material as another casting, then the material properties including strength are identical.
A billet is an intermediate form of aluminum, not a finished product. Aluminum billets get further processed into castings, forgings, rolled shapes and extrusions. These forms receive final heat treatment; a billet is not heat treated.
"Billet" is a colloquialism used by performance parts enthusiasts. It generally refers to a part that would typically be cast or forged into it's rough shape but is instead fully machined from stock.
To me, "billet" simply says our production volume is too small to justify more efficient methods of production.
The real problem isn't tensile strength (for the same HT it will be just slightly lower), it is toughness (lower elongation) and fatigue (much lower also).
There are a bunch of unknowns. If by billet you mean forged bar that is one thing.
If you actually mean billet as in the intermediate breakdown of an ingot then who knows.
One issue that you need to pay attention to is the possibility of directional properties.
We know that castings have these issues, but we usually ignore them in forged or rolled stock.
Transverse strength will be about 5-10% lower than longitudinal, but elongation can be 50% lower.
Page 141 - Standard Mill Terminology
BILLET
A solid semifinished round or square that has been hot worked usually smaller than a
bloom. Also a general term for wrought starting stock for forgings or extrusions.
I am guessing that the context is aftermarket auto parts where people talk about 'billet' housings and wheels and such. All that they mean is that they machined the part (at a huge waste of metal and time) from a rolled or forged shape.
People think that this means that it is strong.
Wheels may the worst. Say a three price wheel where the rings are machined from plate where the L and T properties are 25% different. This could present real issues.
After all we know that real wheels are spin formed or forged into shape.
I meant strong light wheels, those aren't cast.
I watched some truck rims being tested the Alcoa forged wheels ($500-1,000) took over 5x the side load of wheels made any other way.
Like TugboatEng says, its a hot talking automotive performance catch word. A so called billet can be almost any large or small chunk of non finished metal. What is stronger cast or billet? Depends on how the billet is formed. If it is rolled and compressed in some form or fashion, or forged, then the billet will be stronger. That is tensile strength I'm thinking you mean by stronger.
The reason for the billet bragging rights are, the part is then totally formed by machining the features and not just cast or stamped into shape. A preformed forging with consideration given to grain flow, that is fully machined is the strongest and best "billet" machined part. If you want the % difference of strength, do it like they did in the old days, build your part out of the different materials and test them, way to many variables to guess at.
