RETROGRESSION AND RE-AGING

摘要

Over the years, high strength aluminium alloys belonging to 7xxx series have been widely used as aircraft structural material because of their high strength to weight ratio and excellent mechanical properties. But these alloys in the T6 temper condition are s usceptible to stress corrosion cracking (SCC). This could be overcome by using the alloy in overaged condition (T74) which reduces its strength by about 10-15% compared to T6 condition. These shortcomings of combined strength and corrosion resistance could be overcome by multi-stage heat treatment known as retrogression and re-ageing. In the present invention, the properties of retrogressed and re-aged 7010 Al-alloy forgings are studied for two different section thicknesses. The two different section thicknesses samples of forged 7010 Al-Alloy are initially subjected to T6 temper condition. This is followed by subjecting the T6 treated samples to retrogression at 200�C for . different durations in a salt bath furnace. These are subsequently re-aged in accordance with T6 temper condition. The sample thus retrogressed and re-aged is evaluated for different properties like hardness, electrical conductivity and tensile tests. The result obtained through RRA treatment has given rise to a good combination of mechanical properties and stress corrosion crac king resistance. The process thus developed can be implemented during fabrication of upper wing structural components of the aircraft.