The aim of the work is the investigation of the inner structure influence of polycrystalline aluminum alloys on their resistance to deformation and fracture under submicrosecond load duration. The Hugoniot elastic limit, yield strength and critical fracture stresses (spall strength) of aluminum alloys A7, AMz and B95 in as-received coarse-grained state and after the Dynamic Channel Angle Pressing (DCAP) under shock-wave loading were determined.
The method DCAP concerns the methods of high-rate deformation and combines the shock wave and mechanical shear influence [1]. During the DCAP procedure the sample is pressed in the matrix with the crossing channels due to the pressure of blasting powder gases on the pistol or because of the saved kinetic energy at the launch, at that the strain rate of the order of 104-105 c-1 is reached.
All as-received coarse-grained samples of aluminum alloys AMz and B95 had subgrained structure with crystallite sizes of 2-2,5 µm, average grain size of as-received commercial Grade aluminum A7 was ~180 µm. The severe plastic deformation of samples with the DCAP method leads to the formation of complex submicrocrystal structure with the average grain – subgrain sizes 200-650 nm.
The shock-loading pulses with the amplitude up to 5 GPa were created in the samples with a thickness of ~2 mm at collision with flat aluminum impactors, accelerated by high-explosive devices [2] up to velocities 600-650 m/c. The sample thicknesses approximately 5 times exceeded the impactor thickness. The material strain rates before the fracture in the shock experiments were a little higher than 105 c-1. The characteristics of the deformation and fracture process were defined from the analysis of the profiles of free surface velocity of samples, registered with the laser Doppler velocimeter VISAR with high space and temporal resolution [3].
All the tested aluminum alloys demonstrate the growth of the HEL and yield strength after the DCAP processing from 7 to 25%. The spall strength of aluminum alloys weakly variates in interval <10%, but noticeably decreases for commercial grade aluminum A7 in ultra-fine grain state.
The comparison of the results of this work with the known data on strength properties of different UFG aluminum alloys under static and dynamic load conditions has shown the following. The increasing of the strength characteristics of UFG aluminum alloys under shock loading is much less than the one under static conditions. The UFG aluminum alloys tested in this work have the same strength behavior under shock wave loading as the others investigated before [4], so the strength behavior of aluminum alloys after the DCAP processing is very similar to one after severe plastic deformation by the traditional Equal Channel Angle Pressing methods.
The work was carried out in the frames of the project №14-02-31341 of Russian Foundation for Basic Research and the Program № 12-П-21009 of Presidium of Russian Academy of Sciences.
Referenses.
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- Antoun T., Seaman L., Curran D.R., Kanel G.I., Razorenov S.V., Utkin A.V. Spall Fracture. Springer, 2003, p.404.
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- R L Whelchel, N N Thadhani, T H Sanders, L J Kecskes and C LWilliams // Spall properties of Al 5083 plate fabricated using equi-channel angular pressing (ECAP) and rolling. Journal of Physics: Conference Series 500, (2014) 112066.
