The effect of deformation and strain rate on the microstructure refinement of the aluminium alloys (AlCu₄Zr_0.5 and AlZn₆Mg₃CuZr)

Abstract

The well known refinement of grain size by the Severe Plastic Deformation (SPD) methods is the subject of the presented work. The effect of intense deformation is a nanometric feature of microstructure found after SPD in various materials, such as aluminium alloys, iron and many others. The observed changes depended on the properties of the deformed material, its phase composition, stacking fault energy, degree of deformation, strain rate, etc. Nowadays, the influence of strain and strain rate on microstructure is being extensively investigated. Two aluminium alloys: AlCu4Zr0.5 and AlZn6Mg3CuZr were deformed by hydrostatic extrusion. The samples were deformed at a strain rate (έ) ranging from 7.4×101 to 3.84×102s‐1 and in the range of true strains (ϕ) between 1.39 and 2.4. The evolution of microstructure and properties were investigated after deformation. A large amount of microbands and microshearbands was found in the tested samples. The microbands geometry (width of microbands) was analysed statistically and microhardness was measured. It has been found that the microbands show a large misorientation with respect to the matrix. An increase in the strain rate and degree of deformation resulted in a reduction in the microbands width in AlZn6Mg3CuZr alloy. In both alloys the mean width of microbands (d) fell into the range 100÷120 nm after deformation ϕ = 2.4 (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of strain rate on the evolution of microstructure in aluminium alloys

“…In all materials, the reduction of the mean width of the microbands with increasing deformation at the strain rate (in the investigated range) was observed. The smallest AlCu4Zr0.5 ECAP, ϕ = 7 200 nm (Valiev et al, 2000) CEC, ϕ = 14 120 nm (Richert, 2006) HE, ϕ = 2.4 120 nm (Leszczyńska & Richert, 2008) Compression by special laboratory hammer, ϕ = 0.5 114 nm (own) AlMg5 CEC, ϕ = 14 150 nm (Richert, 2006) Compression by special laboratory hammer, ϕ = 0.5 173 nm (own) ECAP -equal channel angular pressing, CEC -cyclic extrusion compression, HE -hydrostatic extrusion.…”

“…The large deformations and high strain rates are the parameters mostly influencing the possibility of forming the bulk nanomaterials. It was found that the high strain rates activate the deformation in the shear bands, microbands and adiabatic shear bands (Giota & Ortiz, 1996;Leszczyńska & Richert, 2008). Observations of the structure of the highly deformed materials show that these elements of the microstructure strongly contribute to the formation of the nanograins, which form inside the mutually crossing microbands (Richert, 2006).…”