A failure of piston pneumatic actuator was observed

which was caused by the fracture of the piston plate.In order to understand the cause for the fracture of piston plate in this batch

the failure analysis of coupling in each case was performed by microstructure observation

chemical composition analysis

scanning electron microscopic analysis.The results show that the fracture of piston plate in this batch belongs to fatigue fracture

which are caused by serious stress concentration existed at the bottom of sealing groove.Meanwhile

a higher strength aluminum alloy 7A19 was used which accelerated the fatigue cracking.Through selecting 5083 alloy

service life of piston plate was improved greatly with technological modification.