A356-T6 Aging at elevated temperatures

[wroberts]

I'm working with A356-T6 Al that has a normal operating temp of 100 degrees C but can go up to 200 degrees C for at most 10 minutes at a shot. My ASM Book Aluminum Alloy Castings Properties, Processes and Applications book has a table (D4.26) that shows 356-T6 material properties at elevated Temps/times and after being brought back to room temperature. At 200 Degrees for 1/2 hour I should be fine and it should have a higher Tensile Strength and Yield Strength after it returns to room temp. There is a chart for A356-T6 (D4.29) but it neglects to shown the material properties after it has been cooled. Is the chart for 356-T6 representaive of the general results after cooling for A356-T6?
Also are the temperature effects additive? If it spends 5 minutes everyday at 200 degrees C for a year is that the same as being held at 200 degrees C for 30 hours?
I don't beive it is but don't really know. If it is additive then the tensile and yield stregth will be reduced.
Any thoughts?
Thanks, Will

 

[Venturini]

The precipitate effect depends on difusion. If you constantly expose the material to a high temperature, the effect will be accumulated because more precipitates will form and eventually they will become incoherent. The behavior of the ageing should be very similar between these two alloys.

 

[swall]

Yes, as Venturini states, the effects of the temperature excursions will be cumulative in regards to the precipitation. You might consider going to the T7 condition (400F age) since your temperature excursions will take you there eventually. But, if you accumulate enough temperature excursions you will eventually overage the T7 condition. There is very little difference in tensile and yield for 356-T6 vs T7. I would also suggest the possibility of using the T51 condition (cast+ 440F age, no solution treat). With T51, you will suffer some loss in room temp mech properties.