【作者】 聂保新；

【导师】 乔军；

【作者基本信息】 辽宁科技大学 ， 材料加工工程， 2012， 硕士

【摘要】 本文主要针对粗晶粒铸轧AZ31和Mg-xAl系合金的高温快速变形性能和变形机制进行了研究。研究得出在475℃（12h） + 425℃（6h）的退火条件下,铸轧AZ31的晶粒尺寸由9.5μm长大到27.8μm。粗晶AZ31在450℃和10^-3 s^-1条件下达到最大延伸率106.7%,由于晶界滑移对应变的贡献降低,延伸率总体低于细晶AZ31。在450℃和10^-3 s^-1条件下的变形激活能为Q = 140.07 KJ/mol,接近Al在Mg中的扩散激活能。结合n≈3的应力指数,溶质牵制位错蠕变在高温低应力下对粗晶粒AZ31的延伸率起到重要作用。在相同应变率下,细晶AZ31的激活能较高,这是由于晶粒细小、晶界密度大,在变形过程中有利于动态再结晶形核,使动态再结晶倾向增加。用真空感应炉制得Mg-xAl （x = 2、3、4）系列铸锭,在400℃进行12 h的均匀化退火,并利用两辊可逆轧机制备3.0 mm厚的板材。研究退火对轧制板材晶粒尺寸的影响,得出在400℃进行60 min退火后,晶粒的平均尺寸较大。在此工艺下,得到粗晶粒Mg-2Al、Mg-3Al和Mg-4Al合金,平均晶粒尺寸分别为120.4μm、55.4μm和78.75μm。以热处理后Mg-xAl系列镁合金板材为研究材料,研究了溶质Al含量对Mg-xAl合金快速塑性变形塑性和变形机制的影响。在同一应变速率和温度下,峰值应力随着Al含量增加而增大。在10^-3 s^-1和450℃条件下,Mg–2Al、Mg–3Al和Mg–4Al的延伸率分别为122.1%、143.7%和139.8%。在相同应变率下,变形激活能随着Al含量的增加而减小。Mg-xAl合金在高应变率(（ε|’） = 10^-2 s^-1)下的变形激活能接近Al原子在Mg基体中的扩散激活能Q = 141.34±10 kJ/mol,结合Mg-xAl合金在450℃的应力指数n≈3,判定Mg-xAl合金在450℃和10^-2 s^-1条件下的变形机制为溶质牵制位错蠕变。更多还原

【Abstract】 In this thesis, annealing conditions and high temperature quick plastic deformation and deformation mechanism of AZ31 and Mg-xAl alloys are investigated.Experimental data show that grain size of twin-roll casted AZ31 grow up from 9.5μm to 27.8μm at the annealing condition of 475℃（ 12h ） + 425℃（ 6h ）. Coarse grained AZ31 reached the maximum elongation of 106.7% at 450℃and 10^-3 s^-1, which is less than fine grained material due to less contribution of grain boundary sliding. The coarse grained AZ31 alloy exhibits an activation energy of Q = 140.07 KJ/mol at 450℃and 10^-3 s^-1, which is similar to the diffusion energy of Al in Mg, Q = 143±10 KJ/mol. Combined with the stress exponent of n≈3, solute drag creep plays an important role during deformation at high temperature and low stress for Coarse grained AZ31. Under the same strain rate, fine grained AZ31 has higher activation energy than coarse grained material because that the high grain boundary density improves dynamic recrystallization.Mg-xAl （ x = 2、3、4 wt.% ） alloy ingot were made in vacuum furnace. Then the Mg ingot were hot rolled with an two roll reversible mill to produce plate with a thickness of 3.0 mm. The effects of annealing time on grain size of the rolled plate were studied. The average grain size reachs its maximum at 400℃for 60 min, under which condition, the average grain siz of Mg-2Al, Mg-3Al, and Mg-4Al are 120.4μm, 55.4μm, and 78.75μm, respectively.The effects of solute content of Al on quick plastic deformation were investigated for the Mg-xAl alloys. The peak tensile stress increases with an increase of Al content under constant temperature and strain rate.Elongations of Mg-2Al, Mg-3Al, and Mg-4Al are 122.1%、143.7% and 139.8% were consistently achieved at 10^-3 s^-1 and 450℃. The activation energy decreases with the increase of Al content under contant strain rate. The activation at high strain rate of （ε|’） = 10^-2 s^-1 for the Mg-xAl alloy is similar to that for diffusion of Al atoms in Mg, Q = 141.34±10 kJ/mol. Combined with the stress exponent of n≈3 at 450℃, it is concluded that solute drag dislocation creep is the dominate deformation mechanism at the strain rate of 10^-2 s^-1 for the Mg - xAl alloys.更多还原