Research On The ECAP Grain Refining Technology, Superplasticity And Isothermal Compression Technological Parameters Of 1933 Alloy

Three aspects of 1933 aluminium alloy imported from Russia are studied in this paper. First, the crystal grains are refined by ECAP technology, and discover what may cause the alloy crystal grain organization the best ECAP technological conditions;Next, the superplasticity of fine crystal material and raw material are investigated separately, and the evolution rule of the superplastic properties and microstructure are researched;finally, the effects of the different isothermal compression parameters on microstructure and room tensile properties of 1933 raw-material (hot rolled block material) are studied.The grain refining test results obtained in this paper show that: ECAP technology has the quite remarkable effect to refine grains. Under ECAP test condition this paper, raw coarse grains can be refined from 20⁵0μm to 7— 12μm. After the samples are pressed in the condition of the 90° ECAP die, route B and 4 passes, the grains could change to be very fine equiaxed-grains, in addition, the high production-efficiency is also obtained. Pressed in case of the best pressing conditions above, the samples anneal at 350℃ for 1h, which is as the optimum heat treatment condition for the superplastic fine crystal organization preparation.The results of the superplastic tensile test present that: the stable microstructure of the 1933 alloy can be achieved as the samples are pretreated via two projects. Project 2 (ECAP technological ,4passes, 350 °C annealing) is the proper superplastic pretreated technology which this paper recommends. The samples present superplaticity in the range of the temperature from 330℃ to 540℃ and the strain rate from 5.5 × 10^-5S^-1 to 3.3 × 10^-1 S^-1.The elongation is in the range of 119%²62%. The optimal superplatic deformation condition is 510°Cand 3.3×10^-4S^-1, on which the maximum elongation is 262% and the flow stress is just only 6.50MPa. Grain boundary sliding is the major mechanism of the superplastic deformation. It shows obvious intergranular fracture.The results of the isothermal compression test show that: the good room temperatures tensile properties are achieved when the raw material is isothermal compressed under six kind of isothermal compression temperatures (350℃ — 450℃ ) and three kind of deformation degrees (20%,40%,60%) separately. Under the identical deformation degree, the different isothermal temperatures have noremarkable effect on room tensile properties and microstructure. After the 410 °C and 390 °C isothermal compressions, the finest microstructure is obtained. Under the identical deformation temperature, the different deformation degrees also have no remarkable influence to isothermal properties and microstructure, and the. fine, uniform microstructure is obtained at 40% deformation degree. In the condition of the identical total compression degrees, the room tensile properties datum close and the microstructure difference is not big also when the isothermal compression of 1 fire time. 3fire times and 5 fire times are carried on separately. The microstructure is finest by a few fires. Although the high density crystal nucleus and the diffused, stable reinforced phases that prevent grain growing effectively can be formed in two aging methods(single aging and double aging), whereas at the single aging, the reinforced phases given by the deposition reinforced phase η' with bulk mass and reinforced ability and GP zone can enhance the tensile properties of the 1933 alloy .however, the microstructure is coarse and non-uniform. The good combination of strength and elongation is obtained at the single aging 1 only;But under the double aging, compared to the reinforced phases formed in single aging, the reinforced phase provided by finer η' with weekly reinforced ability can enable the alloy achieve the good comprehensive properties and fine, uniform microstructure. So the double aging is the optimum heat treatment technology. The room tensile fracture of 1933 alloy is ductile fraction. The fracture mechanism is micropore collective fracture. Brittle fracture appear partly in the single aging.In all, 1933 aluminium alloy, which possesses stable structure properties, good comprehensive properties and good superplasticity, can be isothermal compressed and superplatic formed in wide range of temperature and strain rate.