Influence of Li on the ageing characteristics and microstructure of Al--Cu--Mg--Ag alloy with low Cu/Mg ratio
锂对低Cu/Mg比Al-Cu-Mg-Ag合金时效特性的影响

The influence of lithium on the ageing behavior and microstructure of the low Cu/Mg ratio Al--Cu--Mg--Ag alloys was investigated. The results show that the effect of Li is to increase the rate of hardening, however, the addition of lithium does not progressively change age hardening and precipitation process of Al--Cu--Mg--Ag alloys with low Cu/Mg ratio, and significant age hardening response only occurs with the addition of 2.0\%Li (mass fraction). Transmission electron microscope (TEM) investigation results show that the remarkable increase of age hardness and strength is attributed to the fine dispersion of $\delta^{\prime}$, $Z$ phase and spherical $\delta^{\prime}$/$\beta^{\prime}$ compound particles in the 2.0\%Li--containing alloy.