Heat Treatment of Al 7075 for Ejection Seat Shear Wire

摘要

Shear pins in ejection seats are required to have double shear breaking load values in the range of 46-51 lbs. over the life of the equipment. Aluminum 6061-T6 that was cold worked to increase the shear strength was initially used and performed well for many years. Current lots of Al 6061 could not duplicate the double shear breaking load values and so it was attempted to achieve the required double shear breaking load in the Al 7075 alloy with a stable microstructure. A variety of heat treatments were performed and tested for hardness and double shear breaking load. This report presents the resulting heat treatment curves and the correlation between hardness and double shear breaking load. The proper heat treatment for this application is identified as a solution treatment between 870 and 900 deg F for 32 hours, aging at 225 deg F for 8 hours and then further aging at 350 deg F for 144 hours. This heat treatment was found to produce a double shear breaking load in the required range that is stable over time.