Aluminum die casting material selection

[Andy330hp]

I am currently designing a throttle body for aftermarket EFI systems. Before, all our parts were sand cast A356. Now, we are talking about a move to die cast. I realize that a lot of changes will need to be made, but I have a more fundamental question: which alloy should I use?
I did a search on matweb, which produced 15 possibilities. I also did some more general searches, and A380, 384, and 390 seem like some common numbers. However, "common numbers" is not exactly a basis for material selection.

Stresses are for the most part low, the only stressed area is the flange, and ours is pretty thick so stress is really not even design criteria. Thermal cycling is typical underhood environment (WORST case that OEM's design for would be -40C to 80C). I am most concerned about ease of casting, low porosity (it is a throttle body injection system, so fuel will be present in the part), and decent machining. Thanks

 

[TVP]

Alloy 380/A380 is the most common, with 383 and 390 being next. 383 is the easiest to cast, with 390 being a stronger, but more brittle material. I would start with 380. Porosity is a function geometry, gating, injection profile, etc., not really an intrinsic material property. Vacuum casting techniques like those used by Gibbs Die Casting, Alcoa, and Alcan produce the lowest porosity. I would recommned discussing your design with them before going much further.

 

[Andy330hp]

what is the difference between A380 and 380? I saw both of those on matweb....

 

[TVP]

Not much. The difference is in the maximum allowable levels of the impurity elements. All things being equal, A380 will have higher elongation, impact strength, and fracture toughness than 380.

 

[lgearhart]

Andy330hp, take a look at ASTM B 85, the ASTM spec for aluminum alloy die castings. There's a nice couple of charts in the appendix that will assist your selection. From your noting of desired ease of casting, low porosity, and decent machining, I'd think about 383 in addition to the 380 and A380 choices. As TVP infers, you may be wisest selecting a die caster first, then working with them (alloy selection, gating, process used, etc.) to define your part.

Good luck!

Lee