【作者】 王火生；

【导师】 傅高升；

【作者基本信息】 福州大学 ， 材料加工工程， 2004， 硕士

【摘要】 本研究针对我国当前易拉罐铝材生产中存在的铸锭内部冶金质量较国外的差、热轧加工工艺控制水平较落后等关键问题，采用高效铝熔体综合处理技术制备易拉罐用铝材，通过动态热/力模拟试验以及OM、TEM等现代分析手段，较系统地研究了热变形条件对该材料经均匀化后的高温流变应力行为和微观组织特征的影响规律，并通过试验数据的回归分析等，求解了该材料的材料常数、高温流变应力方程以及热变形微观组织性能的预测模型，探讨了该材料热变形过程中的动态软化机理。获得了以下主要研究结果：（1）各试验条件下，流变应力在达到峰值之后均表现出了不同程度的软化。变形温度对高温流变应力具有显著的影响，在应变速率一定的条件下，随着变形温度的升高，动态软化的趋势也越明显，流变应力降低，峰值应力对应的真应变值减小，进入稳态流变的真应变值则增大。应变速率对高温流变应力的影响较复杂，当应变速率低于1.0s-1时影响较显著，随应变速率的增大，流变应力明显提高，增大，而值则减小；当应变速率高于1.0s-1时的影响减弱。在较高的应变速率和变形温度条件下，流变应力曲线还表现出了多峰值的特征。此外，稳态流变应力与应变速率、变形温度之间满足Arrhenius方程，进一步表明该材料的热变形是受热激活控制的塑性变形过程。（2）采用作图法、最小偏差法和回归分析法求得的易拉罐用铝材的材料常数相当，其中最小偏差法求得的材料常数为：=189.95kJ/mol，=2.16×1013， =5.1914，=0.02185，该材料的热变形激活能远高于纯铝的自扩散激活能，也大于压力罐用铝材的热变形激活能，但低于铸态易拉罐用铝材的热变形激活能。这主要是由于易拉罐用铝材中Mn、Mg等合金元素降低了层错能，使得位错交滑移能力降低，更有利于产生动态再结晶。（3）通过多元线性回归分析，建立了流变应力与应变速率、真应变、变形温度的经验半定量关系；但充分虑到变形条件对加工硬化速率和动态软化速率的影响，又进一步采用Laasraoui与Jonas的峰前应力模型和Jonson-Mehl-Avrami的再结晶动力学模型，求得了更为准确的高温流变应力方程。（4）变形温度对易拉罐用铝材热变形微观组织的影响很显著。随着变形温度的升高，晶粒组织明显长大。变形温度低于400℃时，晶粒分布较不均匀，TEM观察还发现晶粒存在被拉长的趋势，晶内的位错密度也较高。变形温度高于400℃时，开始形成等轴且均匀分布的再结晶晶粒，晶内位错密度较低。应变速率对易拉罐用铝材热变形微观组织的影响较复杂。应变速率低于0.1s-1时晶粒较粗大，晶内位错密度也较低；应变速率高<WP=3>于1.0s-1时，晶粒便出现了被拉长的趋势，晶内位错密度明显升高；应变速率10.0s-1时，通过TEM观察到细小晶粒，该变形条件下可能发生了几何动态再结晶。变形量对微观组织也有明显的影响。变形量较小时，晶粒有被拉长的趋势，个别区域已经出现了细小的再结晶晶粒；变形量50%时，已发生了较充分的动态再结晶，晶粒呈等轴状；随着变形量的进一步增大，再结晶晶粒又一次被拉长。（5）晶粒尺寸d与Zener-Hollomon参数或与稳态流变应力之间存在类似Hall-Patch的关系，说明该材料的组织和性能受Z参数控制，即同时改变变形温度和应变速率而保持Z值不变则可获得一样的热变形组织和性能，该关系可用于易拉罐用铝材热变形组织性能的预测和控制。（6）TEM观察表明，该材料在热变形过程中主要通过重复多边化形成丰富的亚晶组织，通过亚晶的合并长大形成动态再结晶晶核，并通过晶界的迁移完成再结晶晶粒的长大；材料组织中的杂质相、夹杂物和均匀化处理后形成的细小弥散第二相等会阻碍位错运动，提高了变形储能，为动态再结晶创造了有利条件，因此经均匀化处理的易拉罐用铝材较铸态的具有更明显的动态再结晶特征。更多还原

【Abstract】 The influences of hot deformation conditions on the flow stress and microstructures of aluminium sheet used for easy-open-can prepared by synthetical technique of high-efficient melt-treatment of aluminium during hot deformation are studied by using dynamic thermal/mechanical simulation technology and OM and TEM analysis methods, aming at the currently existing problem of internall aluminium sheet used for easy-open-can. The material constants , the flow stress equation, the prediction model of microstructures and properties are derived from experimental data by linear regression analyses. The machanism of dynamic recovery and dynamic recrystallization of the material during hot deformation are discussed. The main results are as follows:(1)There are different dynamic softening phenomenons after peak stress at all experimental conditions. The influence of deformation temperature on the flow stress at elevated temperature is remarkable. The dynamic softening is more obvious, the flow stress and the value of true strain()corresponding to peak stress decrease, but the value of true strain() corresponding to the steady-state plastic flow increase with the increasing of deformation temperature. The influence of strain rate on the flow stress is more complicated. At lower strain rate(),the influence is remarkable, that is the flow stress and the value of increase, and the value of decrease with the increasing of strain rate. When the strain is higher than 1.0s-1, its influence is not obvious. The flow stress curve take on characteristic of multipeak at higher strain rate and deformation temperature. The interrelations of state flow stress ,strain rate and deformation temperature can be described by Arrhenius’ equation, and the result indicates that the hot deformation of the material is controlled by thermally-activated process. (2)The material constants derived by the methods of graphing, linear regression and minimum deviation are to be equal, and the results derived by minimum deviation method are as follows: =189.952kJ/mol，=2.16×1013，=5.1914，=0.0218，the thermally-activated energy of the material is much higher than that of purity aluminium<WP=5>or that of aluminium sheet used for pressure can, and lower than that of as-cast aluminium sheet used for easy-open-can, because the alloy elements such as Mn amd Mg ect., make the fault energy decrease and the cross-slip ability of dislocation decrease, which is favorable to dynamic recrystallization.(3)The semi-empirical equations of the flow stress at elevated temperature are derived from experimental data by polyelement linear regression analysis. Considening the influence of hot deformation conditions on the hardening rate and the dynamic softening rate, we also use Laasraoui and Jonas’s flow stress model before peak stress and the Jonson-Mehl-Avrami model which is used to decribe the kinetics of recrystallization to establish the flow stress model at elevated temperature. The result fit into the pratically measured curves.(4)the influence of deformation temperature on microstructure during hot deformation is remarkable. The recrystallization grains size increases with the increasing of temperature. Whe deformation temperature is lower than 400℃, the distribution of grain structure is not uniform, and TEM analyses also show that the grains are elongated and dislocation density in the grains is high. When the temperature is higher than 400℃, the grains are equixed and distribute uniformly, and the dislocation density in the grains is low. The influence of strain rate on microstructures is complicated. The grains are coarser and the dislocation density in the grains is low when the strain rate is lower than 1.0s-1, the grains are elongated and the dislocation density increases obviously when the strain rate is higher than 1.0s-1.When the strain rate is equal to 10.0s-1, geometric dynamic crystallization might occurre by means of TEM analyses. The influence of strain on microstructure is also remarkable. The grains are elongated and there are few small更多还原