Abstract
The solutionized 7136 Al alloy was heat treated by one-step aging, two-step aging, retrogression and re-aging (RRA) and RRA plus further aging treatment, respectively. The influences of different aging treatments on the precipitation behavior, electrical conductivity and tensile properties were investigated. The results showed that one-step aging treatment forms continuous grain boundary precipitates (GBPs), coherent Guinier-Preston (GP) zone and semi-coherent η’ grain interior precipitates (GIPs). By two-step aging treatment, the GIPs are coarsened and partly transformed into incoherent η phase, which result in a reduction of strength but an enhancement of ductility and electrical conductivity. RRA treatment makes the GBPs to be discontinuous and forms precipitates free zone (PFZ) near grain boundary. The RRA alloy shows similar strength but higher electrical conductivity in comparison with one-step aging. When the RRA alloy further aged at 160 °C, the strength keeps almost constant until 10 h, while the electrical conductivity is increased with increasing aging time. The PFZ is widened and the GIPs become coarser by further aging at high temperature. By contrast, the PFZ is eliminated, accompanying with the formation of GP(II) as further aged at low temperature of 70 °C, therefore a higher strength and lower electrical conductivity are obtained.
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