Normally aluminum alloy 356 is used for castings, and this heat treating process is based upon this metal.
Temperatures and such may vary if you use a different aluminum alloy.
There is some variation in the recommendations for temperatures and times to be used for heat treating aluminum.
These are the values that I use.
It should be noted that some casting folks pull their hot castings out of the sand and immediately quench them in water.
They claim this is all the heat treating they need in order to get a harder and cleaner machining aluminum.
I would recommend trying this first, and if this produces the desired additional hardness, then there is no need to apply the complete heat treating process.
T4 Solution Treatment:
There is a "T4" treatment called "solution treatment", and it consists of elevating the aluminum casting to just below its melting point, and holding it at that temperature for 8 hours.
I have read that some use a shorter period of time, but the white papers say that the solid solution process does not begin until after 6 hours, and thus the 8 hour requirement.
I use 1,000 F for 8 hours for aluminum 356 alloy, followed by an immediate cold water quench.
This temperature must be digitally controlled very carefully, since you are close to the melting point of the aluminum.
Some recommend a hot water quench immediately after this 8 hour period, but I use cold water, and have not had any measurable distortion due to using cold water.
A T4 treatment produces noticeably harder aluminum.
T6 Precipitation Hardening:
If you want the best strength and hardness, then use a second step, which is called "precipitation hardening", and this takes you to a "T6" level.
This step is easy, and can be done by heating the casting to about 400 F for perhaps 4 hours.
No water quench is required after precipitation hardening.
Other's may use different time durations and temperatures, but settings these have worked for me.
I was using raw 356 aluminum castings, and while they machined and drilled ok, they tended to load up the cutting tool, drill bit, saw blade, etc., and were what many including my self called "gummy aluminum castings", ie: not heat treated.
When I used the approximate T6 heat treating method, the aluminum seemed harder, appeared to machine more cleanly, and there was basically no more tool loading.
.
Temperatures and such may vary if you use a different aluminum alloy.
There is some variation in the recommendations for temperatures and times to be used for heat treating aluminum.
These are the values that I use.
It should be noted that some casting folks pull their hot castings out of the sand and immediately quench them in water.
They claim this is all the heat treating they need in order to get a harder and cleaner machining aluminum.
I would recommend trying this first, and if this produces the desired additional hardness, then there is no need to apply the complete heat treating process.
T4 Solution Treatment:
There is a "T4" treatment called "solution treatment", and it consists of elevating the aluminum casting to just below its melting point, and holding it at that temperature for 8 hours.
I have read that some use a shorter period of time, but the white papers say that the solid solution process does not begin until after 6 hours, and thus the 8 hour requirement.
I use 1,000 F for 8 hours for aluminum 356 alloy, followed by an immediate cold water quench.
This temperature must be digitally controlled very carefully, since you are close to the melting point of the aluminum.
Some recommend a hot water quench immediately after this 8 hour period, but I use cold water, and have not had any measurable distortion due to using cold water.
A T4 treatment produces noticeably harder aluminum.
T6 Precipitation Hardening:
If you want the best strength and hardness, then use a second step, which is called "precipitation hardening", and this takes you to a "T6" level.
This step is easy, and can be done by heating the casting to about 400 F for perhaps 4 hours.
No water quench is required after precipitation hardening.
Other's may use different time durations and temperatures, but settings these have worked for me.
I was using raw 356 aluminum castings, and while they machined and drilled ok, they tended to load up the cutting tool, drill bit, saw blade, etc., and were what many including my self called "gummy aluminum castings", ie: not heat treated.
When I used the approximate T6 heat treating method, the aluminum seemed harder, appeared to machine more cleanly, and there was basically no more tool loading.
.
