搅拌摩擦加工细晶AZ31镁合金腐蚀疲劳机理研究

发布时间：2018-08-12 07:40

【摘要】：本文对AZ31镁合金轧制板材进行室温下搅拌摩擦加工,通过空气与水下多道次搅拌摩擦加工得到不同晶粒尺寸的AZ31镁合金。通过在空气中和质量分数为1%NaCl溶液中对加工区进行疲劳实验。主要的结论如下:不同搅拌摩擦加工参数下,加工区得到平均晶粒分别为8.5、3.5、1.2μm的均匀等轴晶组织,平均晶粒尺寸随着热输入量的增加而增加,两道次水下加工制备出1.2μm的细晶组织。加工后织构类型改变且有利于基面滑移。不同加工参数下基面织构的影响相同。空气中的疲劳曲线表现出明显的各向异性,TD方向的疲劳强度高于PD方向,疲劳强度分别为130 MPa和90 MPa。在空气中超细晶镁合金PD方向S-N曲线的拟合方程为:lgN=2.3676-0.068lgσ、TD方向S-N曲线的拟合方程为:lgN=2.2555-0.032lgσ。腐蚀溶液中的疲劳同样表现出各向异性,TD方向的疲劳强度高于PD方向。晶粒尺寸细化能提高腐蚀疲劳强度:首先晶粒细化能够影响变形行为,使得不易变形;其次晶粒细化后在50万周次前能有效的减轻腐蚀,通过以上两种方式提高疲劳强度。织构主要影响变形的难易程度。PD方向,搅拌摩擦加工镁合金的织构利于滑移,可以发现断口处滑移带较多,滑移台阶窄而密;TD方向由于不利滑移,滑移台阶宽且低。母材由于晶粒尺寸大、腐蚀疲劳过程中孪生变形与滑移同时启动,断口表现出滑移带的扭转。
[Abstract]:In this paper, AZ31 magnesium alloy rolled sheet is processed by friction stir at room temperature, and AZ31 magnesium alloy with different grain size is obtained by air and underwater multi-pass friction stir processing. Fatigue tests were carried out in air and in 1%NaCl solution. The main conclusions are as follows: under different friction stir processing parameters, uniform equiaxed grains with average grain size of 8.5 ~ 3.5 渭 m and 1.2 渭 m were obtained in the processing zone, and the average grain size increased with the increase of heat input. A fine crystal structure of 1.2 渭 m was prepared by two subsea processing. The texture type is changed after processing and is favorable to base slip. The effect of basic texture is the same under different processing parameters. The fatigue strength in air is higher than that in PD direction, and the fatigue strength is 130 MPa and 90 MPA, respectively. The fitting equation of the PD direction S-N curve of ultrafine grained magnesium alloy in air is: 1: lgN 2.3676-0.068lg 蟽 and the fitting equation of TD direction S-N curve is: 1: lgN 2.2555-0.032lg 蟽. Fatigue in corrosion solution also shows that the fatigue strength in anisotropic TD direction is higher than that in PD direction. Grain size refinement can improve corrosion fatigue strength: first, grain refinement can affect deformation behavior, making it difficult to deform; secondly, grain refinement can effectively reduce corrosion before 500000 weeks, through the above two ways to improve fatigue strength. Texture mainly affects the degree of deformation. PD direction. The texture of friction stir processing magnesium alloy is favorable to slip. It can be found that there are more slip bands at the fracture surface, and the slip step is narrow and dense TD direction because of unfavorable slip, the slip step is wide and low. Due to the large grain size, the twinning deformation and slip start at the same time during corrosion fatigue, and the fracture surface shows the twisting of slip band.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22

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