Abstract
The microstructural evolution and properties of an Al-Cu-Li alloy with Mg and Zn microalloying (Al-3.5Cu-1.5Li-0.5Mg-0.4Zn-0.3Mn-0.12Zr-0.06Ti) ingot subjected to homogenization (second-step annealing at 500 °C for 24 h following first-step annealing at 400 °C for 8 h) were investigated. Mg-Zn atom clusters were enriched at the end of dendrites as well as low-melting eutectic phases such as S (Al2CuMg), T2 (Al6CuLi3), TB (Al7.5Cu4Li) and T1 (Al2CuLi) in the as-cast alloy. During homogenization, Mg-Zn atom clusters diffused from the segregation to the vacancies, leading to the dissolution of the low-melting eutectic phases. Not only Al3Zr particles were observed at 500 °C, but more fine and uniform spherical dispersoids appeared, which were assumed as Al3(ZrxTiyLi1−x−y). Mg and Zn microalloying can promoted the nucleation of Al3Zr and Al3(ZrxTiyLi1−x−y) dispersoids, as well as T (Al20Cu2Mn3) phases, which all inhibited recrystallization effectively and improve the uniformity of the grains due to the strong pinning effect. The yield ratio was decreased from 0.81 to 0.52 with the yield strength decreased from 172 MPa to 61 MPa, which showed better plastic deformation ability of the alloy subjected to homogenization. In addition, the dissolution of low-melting eutectic phases and formation of Al3(ZrxTiyLi1−x−y) dispersoids resulted in the significant improvement on thermal stability.
Highlights
At present, Al-Li alloys are increasingly being studied as the structural materials with the most potential for development in the 21st century
Metals 2018, 8, 1010 of Mg and Zn to 7XXX series alloys can lead to the formation of η (MgZn2 ) phase during heat treatment [12,13], besides, the addition of Zn can promote the precipitation of T1 phase as Ag-like effect in 2198 alloy [14,15]
The cube samples (15 mm × 15 mm × 1.5 mm) cut from the central part of the ingot were subjected to a two-step homogenization in salt bath furnace, in which the samples were heated at 400 ◦ C for 8 h followed by 500 ◦ C for 24 h and cooled by water quench
Summary
Al-Li alloys are increasingly being studied as the structural materials with the most potential for development in the 21st century. The third-generation Al-Li alloys are widely used in military and aerospace applications because of their superior properties such as low density, high specific strength as well as damage tolerance [1,2]. 1460) [3,4,5], high-plasticity Al-Li alloys containing Ag (such as 2195 and 2198) [6,7] and low-cost Al-Li alloys containing Zn (such as 2060, 2099 and 2A97) [8,9,10]. Metals 2018, 8, 1010 of Mg and Zn to 7XXX series alloys can lead to the formation of η (MgZn2 ) phase during heat treatment [12,13], besides, the addition of Zn can promote the precipitation of T1 phase as Ag-like effect in 2198 alloy [14,15]. The specific mechanism of the influence of Zn on the microstructure and properties of the alloy during solidification, deformation and heat treatment is still unclear
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