heating of magnesium castings

[gearHTr]

We have magnesium castings, alloy AZ91C-T6. Engineering wants to heat these prior to assembly/insertion of steel bearing liner. My question is how to determine maximum temperature these can be heated to. I thought any temperature under the last tempering temp. would be OK.
thanks

 

[TVP]

Since aerospace castings require long cycle times for aging (usually 16 hours at 169 C but possibly 4 hours at 219 C) you should be ok with short-term heating to a temperature just under the aging temperature. I would not use anything greater than ~ 165 C even if the parts were originally aged at > 200 C.

 

[CoryPad]

The maximum temperature allowable will depend on the duration for which the castings will be exposed. MIL-M-6857D MAGNESIUM ALLOY CASTINGS, HEAT TREATMENT OF shows that AZ91C can be artificially aged at 220 [°]C for 4 hours or at 170 [°]C for 16 hours. If the parts will be exposed for a short duration (say 5 to 10 minutes), then I would say 200 to 220 [°]C would be fine. If it is longer, then I would limit the temperature to 170 [°]C.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[will123]

Are these castings shot peened? If not then the suggestions given above are fine.
However if they are shot peened then to avoid degrading the preferential compressive stresses at the surface the exposure temperature should be restricted to no more than 200F (or 93C) according to Mil-S-13165C (Shot peening of metal parts)