doi:

DOI: 10.3724/SP.J.1037.2013.00329

Acta Metallurgica Sinica (金属学报) 2013/49:12 PP.1597-1603

DEFORMATION BEHAVIOR AND MICROSTRUCTURE EVOLUTION OF 7050 ALUMINUM ALLOY DURING SEMI-SOLID STATE COMPRESSION PROCESS


Abstract:
The compression characters of the semi-solid slurries are the key to semi-solid pro- cessing such as semi-solid rolling which has high strain rates during the deformation. The deformation mechanism of semi-solid alloy can be understood well only after the relationship between stress and strain is obtained. Among many relevant research works done up to now, very few studies focus on the 7050 aluminum alloy. In order to study the sensibility of 7050 aluminum alloy to the strain rates, temperatures and reductions, the deformation behavior and microstructure evolution of 7050 aluminum alloy under different compression parameters were studied in this work. The grain coars- ening of 7050 aluminum alloy prepared by the strain induced melt activation (SIMA) method during the isothermal heating process was studied firstly. Then the compression tests, within the semi-solid temperature range, on conventional cast alloy and semi-solid alloy were carried out respectively by using a Gleeble-3500 material thereto-simulation machine with the strain rates from 0.1 s-1 to 10 s-t. The relationship between stress and strain was analyzed subsequently. The synergistic effect between liquid and solid was analyzed in-depth as well. In addition, the differences of cracks propagation between conventional cast alloy and semi-solid state alloy during compression were discussed. Experi- mental results show that the stress of conventional cast alloy has a higher level than that of semi-solid alloy, which is 12 MPa higher at the peak position and 9 MPa higher during the stabilization stage. Reductions, deformation temperatures and strain rates during compression have remarkable effects on the microstructure evolution and the liquid phase distribution. The high reduction leads to the sharp deformation of the grain shape. The deformation has an obvious transition region in the middle which can be clearly seen that elongated grains have a deflection toward the edge. The lower the temperature, the smaller the liquid fraction is. This leads to recrystallization during the compression. The strain rates contribute to the flowing and distribution of liquid phase. The liquid phase transfers hardly when consisting with the solid phase under the high strain rate (10 s-1),which results in a uniform deformation in different regions. Because of the remarkable differences in microstructures between conventional cast alloy and semi-solid alloy, the evolution of cracks propagation is also different, which corresponds to a solid-liquid separation mechanism and a mixed separation mechanism respectively. Semi-solid alloy has spherical crystals that can slide easily when comparing with conventional cast alloy with dendritic crystals. This makes a further explanation for the lower stress of the semi-solid alloy.

Key words:semi-solid aluminum alloy,microstructure,compression,separation between solid and liquid

ReleaseDate:2015-03-06 17:47:01



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