| The Al-Zn-Mg-Cu alloy is widely used in aeronautic industries due to its super-high strength compared with the other conventional aluminum alloys. However, a series of problems such as low fracture toughness and weak stress-corrosion resistance also occur because of its high alloying. By using tensile test, scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction spectrometry, the effect of forming technologies and different heat treatments on the microstructure and mechanical properties of surer-high strength aluminum alloys are discussed. The results show as follow.The most crystalline grains of the 7A04 alloy are equiaxed crystal spheres after spray deposition process and the sizes are 30-70μm. According to the result of X-ray diffraction, a-Al,η(MgZn2) and 0 (CuAl2) are main phases in the alloy. In hot extrusion process, high extrusion ratio and 400℃extrusion temperature are better for 7A04 alloy. Tensile strength of the alloy prodigiously increases after hot-extrusion as 500Mpa. Cause of the anisotropy, the elongation percentage of the extrusion alloy increased.The sizes of grains and precipitated phases are a little big after single solid solution treatment. After two-stage solid solution treatment, the grains are homogeneous distribution and size of them is small. Precipitated phases are tiny material points with wide distance. After the two-stage solid solution, the tensile strength and the elongations of the alloy are better. The tensile strength of the alloy can reach 760MPa with a elongation of 4.8 percent after the two-stage solid solution and the aging treatment. The main way of fracture is ductile fracture after heat treatment.Fracture toughness and tensility of the alloy have been improved by retrogression and reageing (RRA) heat treatment. After the retrogression and reageing treatment (120℃/24h+160℃/2h+120℃/24h), tensile strength and elongation of spray deposition 7A04 alloy are 720MPa and 8.2% respectively. |
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