Abstract
In addition to the three well-known Ag-related precipitates(Ω,X'and Z)in the Al-Cu-Mg-Ag alloys,Ag can also be involved in the formation of the as-cast second phases.However,the effect of Ag ad-dition in Al-Cu-Mg-Ag alloys has not been completely studied and even the structure of the as-cast Ag-containing phases is still controversial.By employing the focused ion beam(FIB)combined with transmis-sion electron microscopy(TEM)techniques and density functional theory(DFT)calculations,the forma-tion mechanisms of the Ag-containing phases in the as-cast Al-Cu-Mg-Ag alloys have been investigated.The Ag-containing phases are a series of hexagonal C14-type Laves phases with continuously varying Ag concentrations,described as(AlxCuyAg1-x-y)2Mg.Moreover,the specific occupancy sites of the atoms in(AlxCuyAg1-x-y)2Mg were determined.The formation of the(AlxCuyAg1-x-y)2Mg can be attributed to the stronger Ag-induced aggregation of solute atoms in the initial stage and the establishment of strong Ag-X(X=Al,Mg and Ag)bonding in the Ag-containing phases.Furthermore,our experiments have revealed the solidification sequence of Al-Cu-Mg-Ag alloys,and pointed out that(AlxCuyAg1-x-y)2Mg is formed at a lower temperature(493.9 ℃)through the reaction L⇌Al2CuMg+(AlxCuyAg1-x-y)2Mg.The study could have positive implications for refinement of the Al-Cu-Mg-Ag quaternary phase diagram and promote the composition-property design of novel aluminum alloys based on(AlxCuyAg1-x-y)2Mg in the future.
基金项目
National Key R&D Program of China(2020YFF0218200)
National Key R&D Program of China(2016YFB0300800)
National Key R&D Program of China(2021YFC1910505)
Innovation Fund Project of GRINM()
NETL
NSTL
万方数据