搅拌摩擦加工超细晶镁合金塑性变形行为研究

发布时间：2018-03-04 18:00

  本文选题：搅拌摩擦加工　切入点：超细晶镁合金　出处：《西安建筑科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：AZ31镁合金是目前使用最广泛的变形镁合金,研究超细晶镁合金的塑性变形行为对镁合金的推广应用具有重要的意义。本文以搅拌摩擦加工(Friction Stir Processing,FSP)制备的AZ31超细晶镁合金为研究对象,采用纳米压痕技术探索FSP AZ31镁合金的塑性变形行为;对FSP AZ31镁合金进行高温拉伸,探索其高温塑性变形行为。主要研究结果如下:FSP加工后的区域,不同载荷下加载过程中曲线的重复性较好,而BM区域有所波动,这与材料的组织均匀性有关。BM的最大压入深度大于FSP各个区域。其中,母材(Basal Metal,BM)搅拌区(Stir Zone,SZ)和前进侧的热机械影响区域(Thermo-Mechanical Affected Zone-Advancing Side,TMAZ-AS)、后退侧的热机械影响区域(Thermo-Mechanical Affected Zone-Retreating Side,TMAZ-RS)的最大深度分别为1244.9 nm,1156.6 nm、1148.3 nm和1142.8 nm。在载荷为5 mN时表现出较高的纳米硬度,其中TMAZ-AS侧的硬度值最高为1.435 GPa。随着载荷增加,镁合金的纳米硬度值下降,表现出明显的尺度效应。在不同载荷下,FSP加工区域的杨氏模量保持不变,而BM的杨氏模量随着载荷的增加而减少。FSP区域的压头下的总位错密度、几何必需位错密度和统计存储位错密度高于BM区域。纳米压痕加载过程中,BM和SZ初始屈服强度分别为0.595 GPa和0.551 GPa,应变硬化指数为0.168和0.169。BM和SZ的宏观抗压屈服分别为0.340 GPa和0.406 GPa,符合Tabor’s压痕理论。FSP AZ31超细晶镁合金有较好的组织稳定性。在不同的变形参数下AZ31超细晶镁合金均表现出了超塑性。其中,在不同温度下,应变速率为3×10-3 s-1,1×10-3 s-1时,材料的延伸率高于应变速率为1×10-2 s-1和3×10-4 s-1时的延伸率;材料在400℃时的超塑性较好。在温度为450℃,应变速率为3×10-3 s-1时,超细晶镁合金的超塑性最好,延伸率为1090.8%。在高温拉伸过程中,镁合金的主要变形机制为晶界滑移,晶界滑移后晶界处产生孔洞,孔洞的汇集使得高温拉伸试样发生断裂。
[Abstract]:AZ31 magnesium alloy is the most widely used wrought magnesium alloy. The study of plastic deformation behavior of ultrafine grained magnesium alloy is of great significance to the popularization and application of magnesium alloy. In this paper, AZ31 ultrafine grained magnesium alloy prepared by friction stir processing Stir processing has been studied as an object of study. The plastic deformation behavior of FSP AZ31 magnesium alloy was investigated by nano-indentation technique, and the plastic deformation behavior of FSP AZ31 magnesium alloy was studied at high temperature. Under different loading conditions, the curves are reproducible and the BM region fluctuates, which is related to the microstructure homogeneity of the material. The maximum indentation depth of. BM is greater than that of FSP. The maximum depth of Thermo-Mechanical Affected Zone-Advancing (TMAZ-ASG) and Thermo-Mechanical Affected Zone-Retreating (TMAZ-RS) of the base metal base Affected Zone-Retreating Side-SZ are 1244.9 nm, 1156.6 nm and 1142.8 nm, respectively. The maximum hardness of thermo-mechanical Affected Zone-Advancing is 1142.8 nm when the load is 5 mn, and the maximum depth of TMAZ-RS is 1244.9 nm, 1156.6 nm and 1142.8 nm, respectively, when the load is 5 mn, the maximum depth of thermo-mechanical Affected Zone-Retreating TMAZ-RSZ is 1244.9 nm, 1156.6 nm and 1142.8 nm respectively, and the maximum depth is 1244.9 nm, 1156.6 nm and 1142.8 nm, respectively. The hardness of TMAZ-AS side is the highest 1.435GPa. with the increase of load, the nano-hardness value of magnesium alloy decreases, showing obvious scale effect. The Young's modulus in the processing area of TMAZ-AS remains unchanged under different loads. The Young's modulus of BM decreases with the increase of load. The geometric required dislocation density and statistical storage dislocation density were higher than those in BM region. The initial yield strength of BM and SZ were 0.595 GPa and 0.551 GParespectively, and the strain hardening exponents of 0.168 and 0.169. BM and SZ were 0.168 and 0.169. BM and SZ, respectively, during the loading of nano-indentation, the initial yield strength of BM and SZ were 0.595 GPa and 0.551 GPA, respectively. It is 0.340 GPa and 0.406GPa. it accords with Tabor's indentation theory. FSP AZ31 ultrafine grained magnesium alloy has good microstructure stability. The superplasticity of AZ31 ultrafine grained magnesium alloy is shown under different deformation parameters. At different temperature, the elongation of the material is higher than that of the strain rate of 1 脳 10 -2 s ~ (-1) and 3 脳 10 ~ (-4) s ~ (-1) when the strain rate is 3 脳 10 ~ (-3) s ~ (-1), and the superplasticity of the material is better at 400 鈩，

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