Effect of low-temperature retrogression and re-aging treatment on the microstructure and properties of 7B04-T651 Al alloy thick plates

The microstructure and properties of retrogression and retrogression re-aging (RRA) treated 7B04-T651 Al alloy prestretched thick plates were studied by transmission electron microscopy, MTS-810 test system and conductivity meter. The results show that the appropriate RRA temper with retrogression at 180± 5℃ for 1 -2h can produce the remarkable improvement in electrical conductivity, with only a 2%-5% reduction in strength below T6. TEM observations of RRA samples show that the precipitation is extremely fine and distributed homogeneously inside the grains, being slightly denser and more stable than that resulting from the T6 temper; whilst the grain boundary precipitation is quite different from that resulting from T6 treatment, the particles being coarser, and much closer to the precipitation resulting from T74 temper.