Shear Behavior of AA6061 Aluminum in the Semisolid State Under Isothermal and Nonisothermal Conditions

Abstract

International audienceThe shear behavior of a 6061 aluminum alloy was studied in the semisolid state at large solid fractions. The tests were carried out either at constant temperature after partial solidification (i.e., isothermal shear tests) or during solidification at low cooling rate (i.e., nonisothermal shear tests). In isothermal conditions, results show that (1) the mechanical behavior depends on the volume fraction of the solid phase present in the sample at the temperature of the test, (2) there is a critical solid fraction corresponding to the coalescence of the solid grains beyond which shear stress increases very sharply with increasing solid fraction, and (3) the mushy alloy exhibits viscoplastic behavior with a strain-rate-sensitivity parameter close to about 0.17. In nonisothermal conditions, results show that stress increases continuously with decreasing temperature whatever the strain rate. However, at high strain rate, it was observed that cracks developed when the solid fraction approaches 1, leading to a slower stress increase compared to that observed at low strain rate. Finally, modeling of this behavior is carried out by considering a cohesion parameter of the solid phase, which depends on solid fraction and strain rate

High temperature compression behavior of the solid phase resulting from drained compression of a semi-solid 6061 alloy

“…The displacement rate has an influence on the stress required to drain the liquid from the specimen: a high strain rate leads to a higher measured stress at a given solid fraction. This strain rate sensitivity is correlated to the viscoplastic behavior of the solid network in this solid fraction range as already observed for tensile [20] and shear [21] Since most of the solidification defects form in the last stage of solidification (i.e. g s > 0.8), only samples machined in the remaining solid obtained after a drained experiment at a high initial solid fraction (i.e.…”

“…2, is shown in Fig. 6: it increases slowly up to a solid fraction of 0.97 and then very sharply when the solid fraction exceeds 0.97 which corresponds to the coalescence solid fraction [20,21]. This sharp increase is due to the fact that, for solid fractions larger than that for coalescence (>0.97), the number of solid bridges increases drastically thus leading to a drop of the solid skeleton permeability and then to more and more difficult liquid flow.…”

Effects of Iron-Rich Intermetallics and Grain Structure on Semisolid Tensile Properties of Al-Cu 206 Cast Alloys near Solidus Temperature

“…Due to the thermal gradients and solidification shrinkage during the casting process, the semisolid microstructure is frequently subjected to tensile stresses, which can lead to casting defects such as hot tearing and porosity [6][7][8]. The response of the solidified microstructure to the applied stress depends on the deformation behavior, tensile properties and liquid flow within the semisolid structure (mush structure) [9][10][11]. To investigate the mechanical properties of aluminum alloys in the semisolid state, three major mechanical tests in shear [7,[12][13], compression [7,[14][15] and tension [4,7,11,[16][17][18][19] have been developed.…”

Process parameter optimizing and studies on microstructure and properties of AZ31 alloy prepared by semisolid rolling process

“…Semisolid processing technique is developed because of its advantages of easy forming, good product microstructure and performances. Therefore, the semisolid processing is regard as an effective technique for magnesium alloy processing [4,5] . Up to now, many slurry preparation processes have been developed [6,7] .…”