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Effect of repeated Heating on 2024-T351

Effect of repeated Heating on 2024-T351

Effect of repeated Heating on 2024-T351

(OP)
I need some help if possible.

My company uses 2024-T351 as bond arbors for bonding liner to the inside of bearing races.  Once the liner is adhered to the ID of the race, a tube shaped bond arbor is inserted into the race and the assembly is placed in an oven.  The standard temperature we use is 315 deg F.  As the assembly heats up, the bond arbor expands and sets the liner to the ID of the race.  It also sets the diameter of the liner due to the amount of expansion that occurs.  

This works really well most of the time, BUT after a while, an arbor that has been producing great parts starts to give us failures in the liner.  These failures include voids under the liner as well as dimensional problems (undersize/oversize).  We have inspected the arbors once they start producing bad parts and the hardness is down, the conductivity is up and the OD is exactly where it was when the parts were new.

As I understand it, the coefficient of thermal expansion does not change with the hardness of the material.  Since it is aluminum, the CTE stays as that of aluminum.  Is this correct?  Would the parts expand faster/slower after repeated heatings?  Does the temperature we are using cause the material to be overaged and how does that affect the pressure we would get at a temperature and the expansion of the part?

Basically, I am looking for anything I can get to help understand why these bond arbors "die" after being run through these heat cycles.

Any help you can offer would be greatly appreciated.

Thanks.

Andrew

RE: Effect of repeated Heating on 2024-T351

Your hardness and conductivity measurements indicate overaging occurred.  This lowered the yield stress and thus the maximum pressure exertable upon the part.  Re CTE, MIL-HDBK-5J, Figure 3.2.3.0, does not indicate any effect of temper upon CTE.

The only imponderable is that the overaged arbors were still the original size, seeming to indicate that yielding had not occurred. A possible reason is that precipitation processes produced a compensating change.  See Aluminum, Vol. I, Properties, Physical Metallurgy and Phase Diagrams, pp.157-161.  Fig. 35 shows that Al 2024-T4 at 300 F undergoes an increase in linear dimension beginning at ~40 hours, with a maximum of 0.16% at ~1000 hours.
As overaging occurred, this dimensional increase may have masked any decrease due to yielding. Perhaps, if you had continued using arbors after ~1000 hrs at 300 F, a decrease in diameter would occur.  I would be interested in knowing time at temperature data for the arbors.

You may get longer arbor use by increasing the wall thickness or using solid barstock.

Hope this helps,
Ken

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