Change of anisotropic tensile strength due to amount of severe plastic deformation in aluminum 2024 alloy

Strength change in anisotropic principal axis directions of an over-aged aluminum 2024 (Al 2024) alloy subjected to equal channel angular pressing (ECAP) was studied. This alloy was subjected to several stages of severe plastic deformation by ECAP. Various strength values were measured using the tension test, the small punch (SP) test and Rockwell and Vickers hardness tests. The SP test was employed due to the size limitation for the tension test specimen in the transverse direction of the ECAP sample. In a previous paper [8], we proposed equations that can assess the tensile strengths in the anisotropic principal axis directions of an anisotropic material using SP test data and showed that the proposed strength assessment equations were very accurate. These equations were used in this study.As the amount of plastic deformation by ECAP increased, the tensile strength in the longitudinal direction of the ECAP-processed Al 2024 alloy was increased. However, considerable change of strength, which is generally predicted, was not observed in this study. In the result of the tensile strength in the transverse direction, the strength even decreased after an equivalent plastic strain of approximately 3.0. It was argued that this decrease was due to the dynamic recovery of the dislocation density during or after ECAP processes at 150 °C. This argument was supported by comparison with the results of the tension test and the hardness test. Based on the results of this study, the strength of an ECAP material must be assessed for both the longitudinal and transverse directions.

► We studied strength change in anisotropic principal axis directions of an ECAP-processed Al 2024 alloy.
► We used small punch test technique to overcome the transverse size limitation of the ECAP rod.
► We found that the longitudinal tensile strength increased as the number of ECAP pass increased.
► We found that the transverse tensile strength decreased after three ECAP passes.
► The strength of ECAP materials must be assessed for both the longitudinal and transverse directions.