Effect on quench rate on the precipitation hardening of Al100-x Lix binary alloys

The quench sensitivity and the effect of lithium content on the precipitation hardening of Al-x at% Li (x = 0.5, 1, 2, 3, 6, and 8) alloys have been investigated by microhardness tests, scanning electron microscopy (SEM),and x-ray diffraction. In addition, the grain-size dependence on lithium concentration has been studied. The results showed that: (i) alloys with less than 6 at% Li are insensitive to quench rate, whereas alloys containing 6 at% Li or more are, to some extent, quench sensitive; (ii) the microhardness increases with increasing lithium content; (iii) SEM results show that the grain size diminishes with increasing lithium concentration both in naturally and in artificially aged specimens, the grain size in artificially aged specimens being greater than that in naturally aged specimens; (iv) the coexistence of δ' and δ phases suggests that small amounts of the δ phase could be precipitated at the expense of the δ' phase via partial dissolution.