The paper proposes a model of strain resistance of alloy under high-temperature deformation. The model describes hardening of alloy due to the increase of dislocation density, as well as the barrier effect of blocking free dislocations, boundaries of grains and subgrains by dispersoids. The model also takes into account the softening processes associated with the recovery and dynamic recrystallization. The model has been tested on the rheological behavior of an Al-Mg alloy named AMg6 at temperatures of 400 and 500 ºC in the range of strain rates from 5 to 25 s -1 . It was found in this temperature -strain rate range that the curve of strain resistance of the AMg6 alloy consists of several portions. First there is hardening of the material, then there is material softening, which is again replaced by hardening of the material. With the use of the electron backscatter diffraction technique and transmission electron microscopy, it was found that the main process of softening at investigated temperatures is dynamic recrystallization. The appearance of the second portion of hardening on the strain resistance curve is the inhibition of dynamic recrystallization, as well as manifestation of the barrier effect of blocking free dislocations, grain and subgrain boundaries by dispersoids.
This work deals with studying the effect of reinforcing SiC particles on the mechanical and plastic properties of a metal matrix composite with a matrix of aluminum alloy AlMg6 (the 1560 aluminum alloy according to the Russian State Standard GOST 4784−97). We assess this effect using the results of mechanical tests at the microscale and macroscale levels. The paper analyzes the fracture mechanism at the microlevel under tensile and compressive stress conditions, as well as the type of contact between the composite constituents. The experimental results obtained for the metal matrix composite are compared with analogous experimental data for the AlMg6 alloy and a compacted material made from the AlMg6 alloy (a compacted powder without addition of SiC reinforcing particles). The studied compacted materials were not previously subjected to extrusion. The tests show a decisive influence of the reinforcing particles on the plastic and mechanical properties of the AlMg6/10% SiC metal matrix composite under compression and tension. For example, the addition of silicon carbide increased the initial yield stress of the compacted material by 26% under tensile tests, and the percentage elongation after fracture was increased up to 1.1%, while it amounted to 0.02% for the compacted material without addition of silicon carbide. Under compression, on the contrary, the addition of silicon carbide degraded plastic properties. As a result, the percentage compression before cracking was 28.4% and 57.9% for the compacted materials with and without addition of silicon carbide, respectively.
The paper deals with a procedure of preparing a specimen surface for the EBSD analysis of a metal matrix composite (MMC) with a high volume fraction of reinforcing particles. Unlike standard procedures of preparing a specimen surface for the EBSD analysis, the proposed procedure is iterative with consecutive application of mechanical and electrochemical polishing. This procedure significantly improves the results of an indexed MMC matrix in comparison with the standard procedure of specimen preparation. The procedure was verified on a MMC with pure aluminum (99.8% Al) as the matrix, SiC particles being used as reinforcing elements. The average size of the SiC particles is 14 lm, and their volume fraction amounts to 50% of the total volume of the composite. It has been experimentally found that, for making the EBSD analysis of a material matrix near reinforcing particles, the difference in height between the particles and the matrix should not exceed 2 lm.
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