Improvements in Strength and Electrical Conductivity in 7B04 Aluminum Alloy Pre-Stretched Thick Plates Via Low-Temperature Retrogression and Re-Ageing Heat Treatments

The effect of RRA treatment with using low retrogression temperatures between 170°C to 190°C on the strength and electrical conductivity (as an indicator of corrosion resistance) of 7B04 aluminum alloy thick plates was investigated. The research results showed that the low-temperature RRA heat treatment provides a means for improving electrical conductivity of the aluminum alloy 7B04 pre-stretched thick plates without sacrificing the mechanical strength. The RRA temper with retrogression at 180°C for 60 min improved electrical conductivity remarkably (reached 21.0MS/m), with only a 3% reduction in strength below T6 temper. Furthermore, TEM observations showed that the microstructure of RRA treated alloy was a very fine distribution of η′ MgZn2 precipitates in the aluminum matrix, similar to T6 condition and η MgZn2 precipitates on grain boundaries distributed similarly to T73 temper.