Resistance spot welding of AZ series magnesium alloys: Effects of aluminum content on microstructure and mechanical properties
Resistance spot welding of AZ series magnesium alloys: Effects of aluminum content on microstructure and mechanical properties
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DOI：
10.1016/j.msea.2014.08.013
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发表时间：
2014-11
期刊：
影响因子：
6.4
通讯作者：
S. Niknejad;Lei Liu;Mokyoung Lee;S. Esmaeili;N. Zhou
中科院分区：
文献类型：
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作者：
S. Niknejad;Lei Liu;Mokyoung Lee;S. Esmaeili;N. Zhou
用光学显微镜和扫描电子显微镜研究了AZ31、AZ61和AZ80镁合金点焊后的组织演变。随着镁基合金中Al含量从3wt%(AZ31)增加到6wt%(AZ61)和8%(AZ80)，熔合区的柱状晶向等轴晶转变和细化作用增强。然而，随着热影响区和熔合区中β-Mg_(17)(Al，Zn)_(12)相数量的增加，AZ61和AZ80焊缝的拉伸剪切强度较AZ31焊缝有所降低。此外，在拉伸-剪切试验中，AZ61和AZ80焊缝在沿熔合面的热影响区失效，这是因为微裂纹优先发生在β颗粒与镁基体的界面。焊后固溶处理显著减少了AZ61和AZ80焊缝热影响区和熔合区的β颗粒数量。这导致了AZ61和AZ80合金焊接强度的提高，因为热处理消除了β颗粒，裂纹扩展到粗晶热影响区，然后扩展到母材。对于热处理后的焊缝，晶粒度是影响其失效模式的主要因素。
The microstructural evolution of the spot welded AZ31, AZ61 and AZ80 magnesium alloys was studied via optical and scanning electron microscopy. As the Al content of the magnesium base alloy increased from 3 wt% (AZ31) to 6% (AZ61) and 8% (AZ80), columnar to equi-axed dendrite transition and grain refinement in the fusion zone were enhanced. However, the increasing amount of the β-Mg17(Al,Zn)12phase in the heat affected zone (HAZ) and fusion zone (FZ) resulted in the reduction of the tensile shear strengths of the AZ61 and AZ80 welds compared to those of AZ31 welds. Moreover, in the tensile-shear testing, the AZ61 and AZ80 welds failed in the heat affected zone along the fusion boundary, because micro-cracking occurred preferentially at the interfaces between β particles and Mg matrix. Post-weld solutionizing treatment was found to significantly reduce the quantity of β particles in heat affected and fusion zones of AZ61 and AZ80 welds. This led to an increase in the weld strengths of AZ61 and AZ80 alloys because the heat treatment eliminated the β particles and cracks propagated into the coarse-grained heat affected zone and then base material. For the heat treated welds, grain size was found as a major factor in the failure mode.