Research On The ECAP Grain Refining Technology And Superplasticity Of LC9 Aluminum Alloy

Aluminum alloy which are nonferrous alloys have been wide use in aerospace industry owing to their attractive properties such as lightweight, low density, high strength, excellent corrosion resistance, good forming property and low cost. Therefore, it is of great significance to research the superplastic properties of these alloys for using superplastic isothermal forging to manufacture complex aviatic forge pieces.The purpose of this paper is to examine the uniaxial tensile behavior, microtructure evolution, fracture behavior and cavitation of LC9 and 2214 aluminum alloy deformed under different conditions, and to determine the optimal structure and process conditions for the best deformation properties of aluminum alloy, thus supplying a reliable basis for obtaining the development and application of the forming technology of aluminum alloy sheets.So the following work has been conducted:ECAP process was adopted to refine the ultra-fine grain LC9 aluminum alloy. The effect of temperature, pass, route and annealing temperature on microscopic have been studied. The microstructure evolution during the deformation was observed by optical microscopy and transmission electronic microscopy. It is demonstrated that ECAP technology has the quite remarkable effect on grain refining. Under ECAP test condition of this paper, raw coarse grains can be refined from 5-15μm to 0.5μm. After the samples are pressed under the condition of the 90° ECAP die, route B and 4 passes, the grains could be refined to be very fine equiaxed grains, in addition, the high production-efficiency is also obtained. When the samples are pressed under the best pressing conditions above mentioned, the samples annealed at 350℃ for lh, which is as the optimum heat treatment condition for the superplastic fine crystal structure preparation.The results of the superplastic tensile test show that the stable microstructure of the LC9 alloy can be achieved as the samples are pretreated via two projects. Project II (ECAP technology, 4passes, annealed at 350℃) is the proper superplastic pretreated technology recommended in this paper. The samples present superplaticity when they deformed under the conditions: in the range of the temperature from 410℃ to 470℃ and the strain rate from 1.1×10^-4s^-1 to 3.3×10^-2s^-1 .The elongation is in the range of 101.3%-406.3%. The optimal superplatic deformation condition is 430℃ and 3.3×10^-4s^-1 , when deformed under the condition, the maximum elongation is 406% and the flow stress is just only 13.2MPa.The experimental result of superplastic tensile test indicates that commercial...