Heat Treating

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solek
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Joined: Wed Apr 16, 2003 6:19 pm

Heat Treating

Post by solek »

I am using aluminum from diesel truck pistons to cast parts for engines. The castings machine well, but problem is the castings are brittle, found this when a connecting rod broke as I pressed in the wrist pin. Does anyone know what heat treatment is needed to make this type of aluminum ductile?
UnkaJesse
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Re: Heat Treating

Post by UnkaJesse »

Solek, I don't know if heat soaking would work or not, but that is what was done at the aluminum plant where I used to work. The coils of metal were put into an oven and held at several hundred degrees F for a day or two to anneal them. 'Course, they were large (2000 pound) coils so it took a while for the heat to soak all the way to the interior.

Wish I knew more particulars, but I don't except for one thing. Another machinist and I had to work in one of those ovens that had just been shut down. Noticed it was pretty warm inside there and our clothes were hot when they touched bare skin so we asked the operator what the temp was inside the furnace at that time. Don't remember exactly, but it was over 300 degrees F with the door open.

Unka(I am a lot older and wiser now and ain't nobody getting me back in one of those ovens, no way!)Jesse
"The same hammer that breaks the glass, forges the steel" Russian proverb
Rich_Carlstedt
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Re: Heat Treating

Post by Rich_Carlstedt »

I am not sure of what material the pistons are made from, nor what parts you are having a problem with other than the conrod..
Here is what most Aluminums do however.
When you cast them, they are totally soft.
As they age, the temper(hardness) goes up for about 30 days and then stops. that is as hard as you will get it. It is called "Precipitation Hardness"
6061 for example, goes from T- (soft) to T-6 (hard) in 30 days
Hard is good for machining ! Its less sticky, and doesn't plug your flutes like soft aluminum
Now if you cast it and need it hard for machining..right away.. You can "Artificially Age" the Alumminun by heat treating it.
You can heat it to 270 degrees for 24-48 hours, or
go to 350 degrees for 8 hours.
To make it soft, which I think you want to get ductility, you need to heat it almost to melting, like 700 degrees.
A way to do that , and maybe someone here knows better, is to use a Oxy-Acetylene torch with a carburising flame.
Play the torch on the part, and it will blacken up with carbon.(soot)
keep heating, and when the carbon suddenly burns off, stop, as you reached the critical point of softening
hope this helps..
I would suggest automatic transmission housings and valve bodies as superior to Pistons for good flow and strength (They use A356 Aluminum)
Rich_Carlstedt
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Re: Heat Treating

Post by Rich_Carlstedt »

I forgot to point out that strength is a function of hardness.
To reach maximum strength of the part, you must wait for 30 days.
so when you soften the part to insert a pin. don't expect it to be as strong as it will be in 30 days.
Check your Machinery Handbook for temper strengths
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Harold_V
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Re: Heat Treating

Post by Harold_V »

I am using aluminum from diesel truck pistons to cast parts for engines. The castings machine well, but problem is the castings are brittle, found this when a connecting rod broke as I pressed in the wrist pin. Does anyone know what heat treatment is needed to make this type of aluminum ductile?

A soak at 950°F and an instant water quench is likely to yield a solution annealed condition, but if you're melting unknown materials, that may not be true.

Not all grades of aluminum are subject to precipitation hardening. Pistons have a high content of silicon, and some of the heat treatable alloys of aluminum contain it as well, so melted pistons are likely a good candidate for heat treat. Alloys commonly found in the shop that are heat treatable are the 2xxx, 6xxx and 7xxx series. They are not known to have good casting properties, however.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Doug_Edwards
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Re: Heat Treating

Post by Doug_Edwards »

If you melted the aluminium in a steel pot, you may have introduced enough iron
in to the material to increase the grain size and cause the castings to be brittle.

Just a thought.

Doug
http://www.precisionlocomotivecastings.com/
Building a 70 ton Willamette in 1.6"
Building a 80 ton Climax in 1.6"

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