Microstructure And Properties Of Al-Zn-Cu-Mg-RE Aluminum Alloy Extrusion

Al-Zn-Mg-Cu alloys have been widely used in aerospace field, military industry and automotive applications because of their high specific strength and specific stiffness, good toughness machinability and other superiority. In order to promote development and application, some appropriate alloying processing and hot working are applied to aluminum alloys to fine microstructure and improve mechanical properties.In this paper, the Al-2.3Cu-2Mg-7.5Zn alloy was chosen as matrix alloy. Two groups of alloys were used in this study. The alloys had same content of Sc element except for that only one group alloy contained Er element. The Al-2.3Cu-2Mg-7.5Zn-0.2Sc-xEr alloys were prepared by melting, casting, and hot extrusion processes. The effect of alloying element Er on the properties of Al-2.3Cu-2Mg-7.5Zn-0.2Sc alloy was studied with tensile tester, fatigue tester, scanning electronic microscope and optical microscope, respectively.The experimental results indicate that the grains in as-extruded and T6 treated Al-2.3Cu-2Mg-7.5Zn-0.2Sc are effectively refined after adding 0.1 wt.% Er. The room temperature tensile strength and yield strength of Al-2.3Cu- 2Mg-7.5Zn-0.2Sc with T6 treated state are improved. The Al-2.3Cu-2Mg-7.5Zn-0.2Sc-xEr alloys without heat treatment can exhibit the cyclic hardening under various total strain amplitudes. The alloys subjected to heat treatment under external total strain amplitude(??t/2 = 0.3%) presents the cycle stability in the late fatigue deformation. After adding Er, cyclic deformation resistance of as-extruded Al-2.3Cu-2Mg-7.5Zn-0.2Sc alloys under the most external total strain amplitude is improved, the cyclic deformation resistance of T6 treatment Al-2.3Cu-2Mg-7.5Zn-0.2Sc alloys under higher external total strain amplitude(??t/2 = 0.4~0.8%)also is increased. After T6 heat Treatment, cyclic deformation resistance of Al-2.3Cu-2Mg-7.5Zn-0.2Sc alloys under the higher external total strain amplitude(??t/2 = 0.4~0.8%) is improved, cyclic deformation resistance of Al-2.3Cu-2Mg-7.5Zn-0.2Sc-x Er alloys under various external total strain amplitude is also increased. The low cyclic fatigue life of Al-2.3Cu-2Mg-7.5Zn-0.2Sc alloys in both T6 treated and as-extruded states can be improved by adding Er. The low cyclic fatigue lives of Al-2.3Cu-2Mg-7.5Zn-0.2Sc-xEr alloys can be enhanced by T6 heat treatment.The fatigue cracks of hot extruded Al-2.3Cu-2Mg-7.5Zn-0.2Sc-xEr with distinct treatment state initiate in a transgranular mode at the free surface of fatigue specimen, and propagate transgranularly.