Solid solution decomposition mechanisms in cast and microcrystalline Al-Sc alloys: I. Experimental studies

Study of Structure and Mechanical Properties of Fine-Grained Aluminum Alloys Al-0.6wt.%Mg-Zr-Sc with Ratio Zr:Sc = 1.5 Obtained by Cold Drawing

“…We believe this finding indicates that during casting and ageing (annealing at 300 °C for 2 h) before drawing, almost a complete disintegration of the supersaturated Sc and Zr solid solution took place in Al followed by the deposition of intermetallic Al 3 (Sc x Zr 1− x ) nanoparticles. This outcome is in agreement with the data in References [28,51] on the kinetics of the disintegration of the Sc and Zr solid solution in Al-Mg-0.22Sc-0.15Zr alloys with different Mg contents (0, 1.5, 3, 4.5 wt.%) where it has been shown that Al-0.22Sc-0.15Zr and Al-1.5Mg-0.22Sc-0.15Zr exhibit intensive deposition of Al 3 (Sc x Zr 1− x ) particles after heating to 240 °C and that after annealing at 300 °C for 2 h a ~50% disintegration of the solid solution takes place alongside with a ~0.4 vol.% deposition of Al 3 (Sc x Zr 1− x ) particles.…”

“…Calculating the stable grain size with the Zener formula d z = 3/4·R z /f v0 [32], the average size of the intermetallic Al 3 (Sc x Zr 1− x ) particles required to stabilize the grain structure in Alloys 1–3 is R z = 180 nm, 325 nm, and 435 nm, respectively. The calculated grain sized R z for intermetallic particles are well aligned with the published experimental data [13,16,17,18,19,23,24,26,28,34], and measurements of the average size of R 0 particles. The difference between the theoretical value R z and the experimentally observed value R 0 is apparently caused by the fact that experimental R 0 is taken as an averaged size of Al 3 (Sc,Zr) and Al–Fe particles.…”

“…(Here, R is the particle size, f v is the volume fraction of the particles, G is the shear modulus, b is the Burgers vector, and k 1 is the numerical coefficient). Many researchers note that the upper limit of increasing the yield strength (Δσ b(max) ) and microhardness (ΔH max ) in fine-grained Al-Sc(Zr) aluminum alloys is visibly lower than in coarse-grained alloys of similar compositions [9,28,29,30]. Existing literature [28] shows that the prime cause for that is the rapid growth of size R z in Al 3 Sc(Zr) particles that are deposited on lattice dislocation cores or grain boundaries in aluminum alloys.…”

“…Many researchers note that the upper limit of increasing the yield strength (Δσ b(max) ) and microhardness (ΔH max ) in fine-grained Al-Sc(Zr) aluminum alloys is visibly lower than in coarse-grained alloys of similar compositions [9,28,29,30]. Existing literature [28] shows that the prime cause for that is the rapid growth of size R z in Al 3 Sc(Zr) particles that are deposited on lattice dislocation cores or grain boundaries in aluminum alloys. As has been shown [31], the diffusion activation energy along the grain boundaries and in lattice dislocation cores is approximately two times higher than the activation energy of a lattice diffusion.…”

“…A common solution to this problem is to dope fine-grained Al-Sc(Zr) aluminum alloys with magnesium (1.5–6 wt.%), which decreases the grain-boundary diffusion coefficient for aluminum [4,9,10,11,12,13,14,15,20,21,28,33,34,35,36,37,38]. This, in turn, shrinks the deposited Al 3 Sc(Zr) particles, facilitates the formation of a finer-grained structure during annealing, and additionally increases the strength and hardness of Al-Sc(Zr) aluminum alloys [10,21,28,34].…”