| Some round bar of6xxx and7xxx alloys for rail vehicle use were produced through smelting&casting, homogenization and extrusion under industrial condition. The reasonable solution&aging process and quench sensitivities of main industrial alloys for rail vehicle use were investigated through mechanical property test, electrical conductivity test, and microstructure analysis as well as computer software simulation. The TTT and TTP curve of these alloys were obtained based on all of the experimental data, and then the results were compared with those of computer simulation. the effect of different cooling rate to the inner stress was analyzed through finite element analysis software. At last,A precise on-line water-miss-wind quenching system were developed under the research which was used in real production line to the sensitivity evaluation. the results shows that:(1) The suitable solution-aging system of6005A alloy is535℃×50min solid solution and water quenching,180℃×6h aging. In this condition, the6005A alloy tensile strength, yield strength and elongation are329MPa,305MPa and14%.(2) The TTT curve and TTP curve of6005A alloy are "C" type, the nose temperature is340℃, the time of gave birth is9s,6005A alloy has high quench sensitivity, The phase transformation kinetics equation of6005A alloy at340℃isothermal treatment is f=1-exP(-0.006t0.9457.)The supersaturated solid solution of6005A alloy decompose and precipitate second phase particles during the isothermal process, and has the maximum rate at the tip temperature of340℃,6005A alloy precipitation sequence is:supersaturated solid solution-β"-β’-β.(3) The best solution quenching and aging technology of extrusion bar of7005alloy is470℃/30min solution, water quenching and with two step aging of105℃/10h+145℃/10h, under this condition, the tensile strength, yield strength and elongation of alloy bar can get to480Mpa,451Mpa and8.4%respectively. Take alloy strength as priority, the effect of every factor of aging process to strength is A>C>B>D, that is:the aging temperature of the first step> the aging temperature of the second step> the aging time of the first step> the aging time of the second step.(4) The TTT curve and TTP curve of7005alloy are"C" type, the nose temperature is285℃, and the incubation period of phase transformation corresponding to the decomposition of solid solution is extremly short in the nose area, which menns that it has very high quenching sensitivity, but it has low quenching sensitivity in the area of high temperature and low temperature. During the on-line quenching, the quenching rate can slow down in the area of high temperature and low temperature, but the quenching rate should exceed6℃/s in the nose area, so as to restrain the presipitates of phase, and ensure the synthesis property of alloy.(5) The TTT and CCT curve of main6xxx and7xxx alloy were simulated and calculated through Jmatpro5.1software, and the results are the same with those obtained by experiment.(6) Abaqus CAE software can simulate the temperature field and stress field at different quenching systems through the curves of physical parameters changing with temperature which get from JmatPro5.1software. Compared with the one-time quenching section, to ensure the basic performance is not declining, sub-quenching can reduce the stress of the alloy.(7) The outlet temperature (the equivalent of online quenching temperature) of6005A profile alloy should be higher than500℃after online extrusion quenching. The speed can be slowed down from500℃to415℃, and higher than9℃/s form415℃to280quenching sensitive areas. For one thing, this can reduce the residual stress. For another, this can avoid the decomposition of solid solution, which can guarantee the mechanical properties.(8) The quenching sensitivity of6061alloy is very high bettween the temperature of250～450℃, and the criticle cooling rate to prevent the precipitate of (3phase is2℃/s, and9℃/s for β" and β’ phase, so for6061Al-alloy the quench rate should be more than9℃/s at the quench sensitivity temperature zone (250～450℃) so as to gain the best properties.(9) The quenching sensitivity of6082alloy is very high bettween the temperature of340～360℃, and the criticle cooling rate to prevent the precipitate of β phase is3℃/s, and15℃/s for β" and β’ phase, so for6082Al-alloy the quench rate should be more than15℃/s at the quench sensitivity temperature zone so as to gain the best properties.(10) The quenching sensitivity of7003alloy is very high bettween the temperature of250～330℃, and the criticle cooling rate to prevent the precipitate of η’ phase is1℃/s, so for7003Al-alloy the quench rate should be more than1℃/s at the quench sensitivity temperature zone so as to gain the best properties.(11) An precise on-line water-mist-wind quenching system was developed based on the former research. And it can be precise controlled in different direction in the circle and axis, and the cooling data can be stored in the form of the die number, and could directly used the next time during production, and could satisfy the quenching requierment of main6xxx and7xxx alloy for industrial use. |
PDF Full Text Request