Preparation Of Nanostrctured 2024 Al, Structure And Properties Based Severe-Plastic-Deformation

Along with the high speed development of aerospace, armament and vehicle, the need of the metallic materials with high performance, especially high specific strength and good ductility, keep in increasingly rising. How to prepare these materials and how to establish the relationship between structure and property are both very important research subject in current field of Materials Science and Engineering around the world. In this dissertation, the severe-plastic-deformation based fabrication, structure and property of nanostructure 2024 Al alloy was investigated, using 2024 Al as experimental materials. The contents and results were summarized as follow:(1) Equal-channel angular pressing (ECAP) of the 2024Al alloy treated by enhanced solid solution has been performed at room temperature, with an imposed equivalent strain of～0.5. A very high hardness of～191 HV and yield strength of～610 MPa in terms of commercial aluminum alloys has been observed for the ECAPed alloy. In addition to the strengthening, this process allows the ECAPed alloy have a moderate level of tensile ductility (～13 %). It is concluded that a low-temperature ECAP processing combined with pre-ECAP enhanced solid solution plus post-ECAP low-temperature ageing is a very effective routes in improving the hardness and strength of commercial 2024 Al alloy.(2) A theoretical calculation based on Taylor equation dealing with strength-dislocation density relationship indicated that the ECAP-introduced dislocation made a considerable contribution to the improvement in strength, about -62.2%. It is believed that ECAP-induced dislocation, fine-particle precipitation, and micro-structural refinement and homogenization are responsible to the modification in tensile properties.(3) The ageing behavior of, the ultrahigh strength 2024 Al alloy fabricated the above-mentioned route consisting of solid-solution plus deformation, was investigated. It is found that the ageing process of 2024Al is speed up by the pre-ageing deformation.(4) The strengthening mechanism of, the ultra-fine sub-grained 2024 Al prepared by over-ageing ECAP, was investigated. The results show that the yield strength of alloy can be described as which is consisted of grain boundary strengthening, dislocation strengthening, sub-boundary strengthening, and the friction stress of lattice.(5) The effect of compressive deformation at liquid nitrogen temperature (LNT-CD) on the 2024 Al alloy with the ultrafine subgrain was investigated. The results show that dislocation brought in by LNT-CD can not be effectively accumulated. This can be ascribed to dynamic recovery, which involved in a sink of dislocation into subgrain boundary. A theoretical calculation indicated that the LNT-CD resulted increase in dislocation density and the strengthening from the rising of the subgrain boundary angle is dominatively responsible for the LNT-CD resulted increase in strength and hardness.