Study On Microstructure And Properties Of High Strength Al-Zn-Mg-Cu Alloy By Spray Forming

In this study, Al-Zn-Mg-Cu alloy ingots with the specifications ofΦ380mm were prepared by automatic control of reciprocating spray forming technology, and its microstructure analysis and mechanical properties of spray-deposited, hot extrusion and heat treatment states through the observation of microstructure, X-ray diffraction, scanning electron microscopy, hardness test, room temperature tensile test etc. And from the spray-formed billet to the whole completion of heat treatment process, studied the microstructures and mechanical properties variation of as-deposited super-high-strength 7475 aluminum alloy, which could provide the basis for application. In addition, for the first time, conducted Friction Stir Welding Experiment on spray-formed 7055 Al Alloys, which could provided basis for solving the connection problems in the practical application of 7055 aluminum alloy. The results are as follows:(1) Using automatic control of reciprocating spray forming technology prepared Al-Zn-Mg-Cu alloy ingots withΦ380mm. The grains of as-deposited billet were equixed shape which mainly in the size from 30 mm to 50 mm, and the microstructures appeared no obvious macro-segregation and ingot density reached 97%.(2) The second-phases in the deposited microstructures of spray-formed 7475 al alloy mainly included reticular phases in grain boundary and transgranular needle-like phases and transgranular near-spherical phases and a few blocky phases. The second-phases in grain boundary contained a large number of Zn and Cu, and the transgranular precipitated phases were MgZn2, as well as a small amount of Al2CuMg.(3) After T6 heat treatment, the second-phases in the deposited microstructures of spray-formed 7475 aluminum alloy reduced, even disappeared, and the boundary narrowed. In the crystalline, needle-like phases vanished and the second phase dispersed. EDS analysis showed that the grain boundary of the second phase of the Mg, Cu, and Zn from 5.94%, 9.41% and 27.58% down to 2.33%, 1.65% and 7.73%, respectively.(4) After the extrusion, the primitive grain boundary of as-deposited material vanished and the reticular phases was disrupted and the grain broke up. The microstructure was more compact and more tiny crowded second-phases precipitated. The ultimate tensile strength of the large-scale materials at T6 state was increased to 629.9MPa, and the elongation was 12.4%. (5) 7475 Al alloy by spray forming is a clear age-hardening alloy, 475~480℃/4~5h is a more reasonable solution process, after 120℃/24h aging alloy can achieve peak performance.(6) It's the first time for the successful realization of friction stir welding of 4mm thick 7055 Al alloy plates by spray forming, when choosing the appropriate welding parameters, the weld appearance is beautiful and excellent, receiving almost no deformation of the plate butt weld. Preliminary research show that welding parameters can be used as follows: the rotation speed of mixing head is 800r/min; Welding speed is 100mm/min; the depth of welding control shaft shoulder pressed into the workpiece is 0.1mm, with an inclination of 3°, weld tensile strength is 457.1MPa, reaching the strength of 77% of the base metal. The welding process, as well as post-weld heat treatment process needs further exploration and study.