Influence of technological parameters on microstructure and mechanical properties of FSW AZ31 magnesium alloy joints
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摘要: 以AZ31镁合金为研究对象,采用数值模拟和工艺试验相结合的方法,系统研究了焊接工艺参数对搅拌摩擦焊接头温度场分布、微观组织以及力学性能的影响. 有限元数值模拟的结果表明,随着转速的增加或焊接速度的降低,接头产热逐渐增加,接头上层温度明显高于下层温度,说明搅拌摩擦产热主要来源于轴肩的摩擦运动,而搅拌针摩擦运动和材料的塑性变形只提供了少量的产热. 工艺试验结果表明,随着焊接速度的增加,接头晶粒尺寸降低,且组织均匀性得到改善. 随着转速的增加,接头晶粒尺寸不断增大,过渡区晶粒的均匀性变差. 拉伸过程中裂纹在焊核区与热力影响区之间的界面处萌生和扩展. 其中,转速为1400 r/min、焊接速度为300 mm/min的接头具有较好的力学性能,断后伸长率为16.5%,抗拉强度为252 MPa,分别达到母材的75%和90%.Abstract: The effect of technological parameters on the temperature field, microstructure and mechanical properties of AZ31 magnesium alloy was studied by means of numerical simulation and experiments. The results of simulation show that heat generation of the joint increases correspondingly with the increase of rotate speed or the decrease of transverse velocity, and the temperature of the upper part is significantly higher than that in the lower part, which indicates that the heat generation mainly comes from the friction motion of the shoulder, while the stir pin and the plastic deformation of the material only provide a small amount of heat generation. The technological tests show the grain size of the joint decreases and the microstructure homogeneity is improved with the increase of welding speed. With the increase of rotate speed the grain size of the joint increases and the uniformity of the thermo-mechanical affected zone become worse. The rotate speed 1 400 r/min and welding speed 300 mm/min joint obtained best mechanical properties, i.e. elongation and tensile strength are 16.5% and 252 MPa, reaching 75% and 90% of the base material, respectively.
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图 6 焊接速度为200 mm/min时不同转速下AZ31镁合金接头不同区域的金相组织
Figure 6. Microstructure in different positions of AZ31 magnesium alloy joints with the welding rate of 200 mm/min. (a)1 000 r/min-stir region;(b)1 000 r/min-interface region;(c)1 400 r/min-stir region;(d)1 400 r/min-interface region;(e)1 800 r/min-stir region;(f)1 800 r/min-interface region
表 1 AZ31镁合金的化学成分(质量分数,%)
Table 1 Chemical composition of AZ31 magnesium alloy
Mg Al Zn Mn Fe Ca Si 95.475 3.1 0.89 0.38 0.005 0.05 0.1 表 2 AZ31镁合金搅拌摩擦焊接头的力学性能指标
Table 2 Mechanical performance index of FSW AZ31 magnesium alloy joints
转速
n/(r·min−1)焊接速度 v/(mm·min−1) 抗拉强度 Rm/MPa 断后伸长率
A (%)1 400 100 263 5.0 1 400 200 241 7.5 1 400 300 252 16.5 1 000 200 227 5.0 1 800 200 198 3.0 -
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