转速对铝/镁搅拌摩擦焊接头金属间化合物及低熔点共晶的影响

Effect of Rotational Speed on Intermetallic Compounds and Low Melting Point Eutectic of Al/Mg Friction Stir Welded Joints

研究了转速对铝/镁搅拌摩擦焊接头金属间化合物和低熔点共晶的影响,并用电子背散射衍射表征了铝侧和镁侧界面微观结构。结果表明,当采用375 r/min的低转速时,镁侧界面上部出现由Mg固溶体和Al_(3)Mg_(2)相组成的共晶层,平均厚度为38.83μm。在镁侧界面上部还发现一层厚度为12.3μm的连续柱状Al_(3)Mg_(2)层,垂直于Al_(3)Mg_(2)层与共晶层的边界。在镁侧界面的中部和底部,只有Al_(3)Mg_(2)层和Al_(3)Mg_(2)层,其厚度沿厚度方向从上到下依次减小。此外,铝侧和镁侧界面的Al_(3)Mg_(2)层具有较高的平均晶粒取向差,这为铝和镁原子间的扩散提供了一条途径。当转速为600 r/min时,Mg固溶体与Al_(3)Mg_(2)相组成的共晶层沿厚度方向分布在镁侧界面上,共晶层厚度较低转速(375 r/min)时显著增加。镁侧界面上部的Al_(3)Mg_(2)层和共晶层的平均厚度分别为32.89和68.92μm。最后,由转速引起的应变速率对金属间化合物的生长起着重要作用。

The effects of rotational speed on the intermetallic compounds and low melting point eutectic of Al/Mg friction stir welded joints were investigated.The interfacial microstructures of both Al and Mg sides were characterized by electron backscatter diffraction.The results show that when the low rotational speed of 375 r/min is used,the eutectic layer(Mg+Al_(3)Mg_(2)),with an average thickness of 38.83μm,appears at the upper of the Mg side interface.A continuous columnar Al_(3)Mg_(2)layer with a thickness of12.3μm,perpendicular to the boundary between the Al_(3)Mg_(2)layer and eutectic layer,is also found at the upper of the Mg side interface.At the middle and bottom of the Mg side interface,there are merely Al_(3)Mg_(2)layer and Al_(3)Mg_(2)layer,the thickness of which decreases sequentially from the upper to the bottom along the thickness direction.In addition,the Al_(3)Mg_(2)layer with high kernel average misorientation at the Al and Mg side interface provides a path for the diffusion of Al and Mg atoms.When the high rotational speed of 600 r/min is used,the eutectic layer composed of Mg solid solution and Al_(3)Mg_(2)phase is distributed across the Mg side interface along the thickness direction,and the thickness of the eutectic layer increases significantly compared with that at the low rotational speed of 375 r/min.The average thickness of the Al_(3)Mg_(2)layer and eutectic layer on the upper of the Mg side interface is32.89 and 68.92μm,respectively.Finally,the strain rate caused by rotational speed plays an important role in the growth of intermetallic compounds.