| The effects of alloying elements and various heat treatments process on mechanical properties, stress corrosion crack (SCC) property, fracture toughness and microstructural evolution of 7475 high strength aluminum alloys were investigated by means of the tensile test, SCC test, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). And the heat treatment regimes were optimized by analyzing the experimental results. The conclusions are summarized as follows:1. 7475 aluminum alloy has a wide range of solution temperature and the proper solution temperature is 470℃. SEM observation shows that after solution treated at 470℃for 1h, residual particles in the matrix are Al7Cu2Fe and Al2CuMg (S phase).2. The aging treatment practices of 7475 alloy sheet are summarized as below:T6: aging process parameter: 120℃/24hT76: aging process parameter: 107℃/8h+163℃/15hT73: aging process parameter: 107℃/8h+163℃/30hRRA: aging process parameter: 120℃/24h+200℃/7min+ 120℃/24h3. The addition of minor element Cr can greatly increase the strength of the alloy although the ductility of it decreases slightly. After T6 heat treatment (120℃/24h), the tensile strength, yield strength of the Cr-free 7-c alloy is 543MPa and 510 MPa, respectively. While in the Cr-containing 7-1 alloy, the tensile strength and yield strength reach as high as 589MPa and 554 MPa, increased by 8.5%, 8.6% respectively, compared with Cr-free alloy.4. The tensile strength of 7475 alloy after T73 process increases obviously with increasing of Zn, Mg, Cu content. The tensile strength of 7-2(upper limit of composition), 7-1 (middle limit of composition), 7-3(lower limit of composition) alloy is 525MPa, 519MPa and 476MPa, respectively. Meanwhile the fracture toughness decreases with increasing of Zn, Mg, Cu content, the fracture toughness of the three alloys is 35.3 MPa .......(?), 36.1 MPa·(?) and 38.3 MPa·(?), respectively. |
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