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Lm25 alloy treatment

Lm25 alloy treatment

Lm25 alloy treatment

Are oil pump castings found in most cars heat treated? The castings I refer to are the common design where metal pump rotors run inside the casings. Ive searched and searched this topic and cannot find a definite answer. Ive read that If I do heat treat be it(reworked casing design, gravity cast) in solution at 540 degrees(approx from memory for x amount of time) That this heat treatment will only be of use if the casing never sees a temperature of over 130 degrees.
The surfaces Im worried about are the end sections of casing where the most rotor contact is, granted there is an oil film there.

I know the above its a bit approximate but Im just after some pointers so I can look into whatever I need to do to get this done.

So to sum up.
Is gravity cast lm25 ok for the above without heat treatment?
Or should I heat treat bearing in mind the casings may see over 130degrees?

Thanks as always in advance,


RE: Lm25 alloy treatment

Sorry Pat, the coffee hadn't kicked in,

Its Lm25 aluminium alloy.
And Im referring to 130'degrees Celsius. Ive seen my oil temps to go more than that when pushing it on.
Ive read that over 130'c can effect any treatment to lm25?
I dont know if I should believe it or not.


RE: Lm25 alloy treatment

I don't know for aluminium. I knew iron would be no problem.

I am no metallurgist, but I think even moderate temperatures can impact on the dimensional stability of aluminium.

I once built a prototype for a plastics welder and it had aluminium bars as part of the heat transfer medium. It had to maintain quite high accuracy re crush on the plastic film and I remember I had to buy a very special grade of aluminium to maintain dimensions after repeated heat cycling in the range of 120 to 150 deg C. That was 10 years ago so the details are now gone from memory except T7 I think.

Also, I did have a quite souped up VW Beetle many many years ago. They have an aluminium oil pump set in a housing. As oil is a major part of the cooling system, it gets quite hot. 130 deg C was about maximum I think until Mobil 1 and AmsOil hit the market. I could then push it to about 150C

I never had oil pump issues. I don't know the alloy, but I always hard anodised them to reduce clearances and improve life.

I hope this only slightly relevent ramble helps.

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RE: Lm25 alloy treatment

It does indeed help Pat thanks. I know the beetle pumps only too well, face mounted with the drive shaft out the rear.

Had you any problems anodizing cast alloy no?
I just read there in an cast alloy book that it will obtain its full hardness in 12 months by its-self anyway, I should have started sooner!

I might test try anodizing on a scrap casting, see how I go.

Thanks Pat.

RE: Lm25 alloy treatment

As LM25 (AA356) is a heat treatable casting alloy, it would not really make sense to use it un heat treated, when cheaper alloys, would suffice. But, it would help us better answer your question if you told us what exactly you are trying to do.

RE: Lm25 alloy treatment

I have a different shape oil pump casing cast from it, and it is also fully machined to accept 2 rotors as seen in many factory pumps. Where these rotors bear on casing top and bottom(+ clearance tolerance) Im am worried if I should heat treat the casing to prevent axial wear that may occur over time from the spinning rotors. It is an oil pump keep in mind, so ample amounts of oil will exist between all moving parts at all times.

Hope this sheds more light on my problem, if not Ill answer anything else that may be needed in order to get to the bottom of this.

Thank you.



RE: Lm25 alloy treatment

When you say that "so ample amounts of oil will exist between all moving parts at all times", have you considered the possibility of briefly uncovering the pickup for any combination of reasons?


RE: Lm25 alloy treatment

Its not a common setup, its part of a scavenge system and low pressure, and there will always be 'a pipe full' of oil above it.
Ive also seen many car(s) with alloy heads with cams fitted directly to them(no shells) to run so dry that the crank locked solid due to blocked pickup. On inspection the head was ok as were journals and it has done 60k miles since.

I dont see how anything like that matters though really, all I need to know is if lm25 has good bearing properties in its raw cast state or should I treat it, and what is the best method. Its more so a general question really. Should I or should I not?

Thanks again folks.


RE: Lm25 alloy treatment

Increasing the hardness of the casting via heat treatment (T6) will improve the wear resistance to a degree. If the casting is already heat treated, you will not mess things up with a second heat treat. But to really enhance the wear resistance, you need to consider anodize as patprimmer suggested. It is hard to get a good film build on the aluminum silicon alloys, but you should be able to get a hard anodize film close to .001". You could also look at electroless nickel as an alternative to hard anodize.

RE: Lm25 alloy treatment

I have just poured the castings last week, so no they have no treatment as they sit now. What treatment would you recommend> T6?
Anodizing sounds good also, noted.

You reckon it does need some for of treatment though to improve wear resistance yes? I dont know why I thought It may be ok as is.

Swall, thanks for your reply, solid info is good.

RE: Lm25 alloy treatment

And just to add, is is a one off 'seeing' of 130 degrees that will return it to its normal 'soft' state or does it take many cycles?  

RE: Lm25 alloy treatment

As the ageing temperature for this alloy is 300F,(following a solution treatment of 1000F), your operating temperature of 130C (266F) will not degrade the hardness. It probably will craze crack the hard anodize film, although that is an issue only in situations where corrosion is involved. Additionally, aluminum casting alloys typically exhibit improved machinability in the T6 condition, compared to as-cast.

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