RRA Heat Treatment of Large Al 7075-T6 Components

Abstract

Retrogression and re-aging (RRA) is a heat treatment process performed on the aluminum alloy 7075 in the T6xxx temper condition to improve its resistance to corrosion, while at the same time maintaining the high strength levels required for aircraft structural applications. For large extruded or forged parts, we have determined that the most practical process involves retrogression at 195 degrees centigrade for 40 minutes, followed by rapid cooling and full re-aging at 120 degrees centigrade for 24 hours. After an RRA treatment of a large extrusion (a three-metre section from a CC-i 30 sloping longeron), we measured a shrinkage of approximately 0.015%, with minimal distortion damage.