Solidification phases and their evolution during homogenization of a DC cast Al–8.35Zn–2.5Mg–2.25Cu alloy

Microstructure, mechanical properties and stress corrosion cracking of Al–Zn–Mg–Zr alloy sheet with trace amount of Sc

“…There is a clear endothermic peak at temperature 476.7 ºC. It has been discussed by Liu et al [29] as well as by He et al [30] that the peak corresponds to the melting of α-Al matrix and η-MgZn 2 , which implies that the start melting temperature (T m ) of the alloy ingot is 476.7 ºC. Considering the accuracy of furnace, the temperatures ranging from 460 ºC to 480 ºC were selected in this paper.…”

Effect of Sc and Zr Additions on Recrystallization Behavior and Intergranular Corrosion Resistance of Al-Zn-Mg-Cu Alloys

“…The backscattered electron (BSE) images in the large magnification show that in both alloys the large intermetallics were mainly located at the grain boundaries or the intersection between grain boundaries while the much finer dispersive precipitations were distributed in the grain interior, as shown in Figure 3 c,d. For Al-Zn-Mg-Cu-Zr alloy, according to the result of EDS analysis, the large intermetallic (spectrum 1) was suspected to be the Mg(Zn, Al, Cu) 2 particle, one of the residual non-equilibrium phases that were widely mentioned in the previous investigation about the high Zn content Al-Zn-Mg-Cu alloys [ 30 , 31 , 32 ]. For Al-Zn-Mg-Cu-Sc-Zr alloy, the residual non-equilibrium phase (spectrum 2) should be the Mg(Zn, Al, Cu) 2 particle with a different atom ratio, but the intermetallic particles (spectrum 3) with the square shape remained both at grain boundary and in the grain interior, which should be the primary Al 3 (Sc 1−x Zr x ) phase with high stability [ 33 , 34 ].…”

Microstructure Evolution and Recrystallization Resistance of a 7055 Alloy Fabricated by Spray Forming Technology and by Conventional Ingot Metallurgy

“…It is well known that the solidification of conventionally cast 7055 alloy is accompanied by varying degrees of micro-segregation of alloying elements due to their partitioning between liquid and solid phases during solidification, and due to the non-equilibrium dendritic solidification. [12] The spray forming technology can effectively avoid this phenomenon due to the rapid solidification and without a characteristic dendritic structure. In general, because of this special forming process, the type, size and distribution of primary phases, the composition, and the grain structure are changed in the spray-formed 7055 alloy.…”

“…Many studies have documented that the white phase in Figure 2 is the Mg(Zn, Cu, Al) 2 phase, which has a similar structure as MgZn 2 containing Al and Cu, while the gray phase in Figure 2(b) (as-cast) is the Al 2 CuMg phase. [12,13] However, no such Al 2 CuMg phase embedded in the coarse Mg(Zn,Cu,Al) 2 phase is observed in the as-deposited 7055 alloy.…”

“…A homogenization heat treatment is an indispensable process for traditional casting alloys, aiming at dissolving large size eutectic phases, redistributing the solute, eliminating intragranular segregations, i.e., level out compositional variations, reducing internal stresses and removing other casting defects. [12,13] Besides, in 7xxx aluminum alloys with small additions of zirconium, coherent Al 3 Zr dispersoids are precipitated during homogenization, which may have a significant effect on inhibiting recrystallization so that alloys maintain their deformed microstructure during possibly subsequent high temperature exposure. [14][15][16] Hence, alloys may obtain excellent mechanical properties via the combination of their stable deformed substructure and Al 3 Zr precipitation hardening.…”