Bearing Stresses and Surface Loads of Magnesium Alloy AZ92A

[KHI]

I am not sure as to how to explain what I am looking for but I will attempt to give it a good try.

We are presently in the process of designing a housing which will be cast from Magnesium alloy AZ92A. In reviewing the requirements of FAR Part 25 Section 25.621 Casting Factors. The casting that is being designed is not thought to be a critical casting. It serves as a housing for rotating components that supply air to the cabin and cockpit. The housing is attached to a support sturcture in the airframe. The only surface loading would be from the result of torwuing froces applied by the attaching hardware, which would be compression on the housing and the support structures. Any help in clarification of the issue would be greatly appreciated.

 

[TVP]

It sounds to me that you would use the appropriate casting factor for non-critical castings, with the specific value dependent upon the items described in Section 25.621. Neither MMPDS nor MIL-HDBK-5 list bearing properties for Mg castings, but there is some data available from other references like "Magnesium Product Design" by R.S. Busk. The ASMH may also have this data, but my copy is at home.

 

[WKTaylor]

KHI... Briefly...

If You have a part that is this lightly loaded, why not make from molded heat/weather resistant glass-fiber reinforced plastic, such as fiberglass filled nylon 6/6 [ASTM D4066]... epoxy-fiberglass mat?

Otherwise suggest You make from AZ92A-T4 or -T6 per ASTM B80; except meet requirements of AMS2175 Class C Grade C or (if feasible) Class D Grade C [I rarely recommend Grade D].

FYI MIL-HDBK-5 [basic, Aug 1962] has complete mechanical properties for AZ92A sand and permanent mold castings per QQ-M-56 [trick is trying to determine what quality level the casting samples were maded equivalent to].

Regards, Wil Taylor