Microstructure and mechanical properties of weld-bonded and resistance spot welded magnesium-to-steel dissimilar joints
Microstructure and mechanical properties of weld-bonded and resistance spot welded magnesium-to-steel dissimilar joints
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DOI：
10.1016/j.msea.2011.12.096
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发表时间：
2012-03-01
期刊：
影响因子：
6.4
通讯作者：
Zhou, Y.
中科院分区：
文献类型：
--
作者：
Xu, W.;Chen, D. L.;Zhou, Y.
本研究的目的是评价镁与镁(镁/镁)异种焊接头和镁-钢(镁/钢)异种钢焊接接头的组织、拉伸和疲劳性能，并与电阻点焊(RSW)镁/钢异种接头进行比较。在WB镁镁接头中，熔合区(FZ)形成了等轴枝晶和离异共晶组织。在RSW和WB镁/钢异种接头中，FZ只出现在等轴晶和柱状晶的镁侧。在钢侧，WB镁/钢接头的显微组织没有变化，而RSW镁/钢接头的显微组织由板条马氏体、贝氏体、珠光体和残余奥氏体相组成，导致显微硬度增加。较低的冷却速度抑制了WB镁/钢接头中缩松的形成，但促进了镁/钢接头中镁锌和镁锌的形成。添加的粘结层减少了焊核周围的应力集中。在最大拉伸剪切载荷和能量吸收方面，WB镁镁和镁/钢接头均明显强于RSW镁/钢接头，且随着应变率的增加而增大。WB镁镁和镁/钢接头的疲劳强度是RSW镁/钢接头的三倍。在较低载荷水平下，RSW镁/钢接头的疲劳失效发生在缺口根部附近的热影响区，而在较高载荷水平下，疲劳失效模式为界面断裂，而在最大循环载荷达到10kN时，WB镁/镁和镁/钢接头的疲劳失效发生在镁母材中。(C)2011爱思唯尔B.V.保留所有权利。
The aim of this study was to evaluate microstructures, tensile and fatigue properties of weld-bonded (WB) magnesium-to-magnesium (Mg/Mg) similar joints and magnesium-to-steel (Mg/steel) dissimilar joints, in comparison with resistance spot welded (RSW) Mg/steel dissimilar joints. In the WB Mg/Mg joints, equiaxed dendritic and divorced eutectic structures formed in the fusion zone (FZ). In the dissimilar joints of RSW and WB Mg/steel, FZ appeared only at Mg side with equiaxed and columnar dendrites. At steel side no microstructure changed in the WB Mg/steel joints, while the microstructure in the RSW Mg/steel joints consisted of lath martensite, bainite, pearlite and retained austenite leading to an increased micro-hardness. The relatively low cooling rate suppressed the formation of shrinkage porosity but promoted the formation of MgZn2 and Mg7Zn3 in the WB Mg/steel joints. The added adhesive layer diminished stress concentration around the weld nugget. Both WB Mg/Mg and Mg/steel joints were significantly stronger than RSW Mg/steel joints in terms of the maximum tensile shear load and energy absorption, which also increased with increasing strain rate. Fatigue strength was three-fold higher for WB Mg/Mg and Mg/steel joints than for RSW Mg/steel joints. Fatigue failure in the RSW Mg/steel joints occurred from the heat-affected zone near the notch root at lower load levels, and in the mode of interfacial fracture at higher load levels, while it occurred in the Mg base metal at a maximum cyclic load up to similar to 10 kN in both WB Mg/Mg and Mg/steel joints. (C) 2011 Elsevier B.V. All rights reserved.