Effect of Mg content on quenching sensitivity relative to yield strength of ultra-high strength aluminum alloy
The effect of Mg content(1%,2%and 3%,mass fraction)on the quenching sensitivity relative to yield strength of Al-Zn-Mg-Cu alloy was studied by immersion end-quenching technique,room temperature tensile test,electrical conductivity test,calculation of phase diagram and continuous cooling transformation diagram,scanning electron microscopy,electron backscatter diffraction and transmission electron microscopy.The results show that higher content of Mg leads to higher reduction rate of yield strength due to the decrease of quenching rate,and therefore quenching sensitivity is higher.The quenching-induced phases in the alloys are η and T phase.The increase of Mg content increases the critical quenching rates for precipitation,the quantities and sizes of these phases.Combined with the results of electrical conductivity and quenching-induced phase area fraction,the mechanism of Mg content affecting quenching sensitivity was discussed in terms of the difference of driving force and nucleation sites for precipitation of quenching-induced phase.
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