\r张 旭¹，罗 震¹，毕 敬²，张 禹\r¹\r
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AuthorsHTML:\r张 旭¹，罗 震¹，毕 敬²，张 禹\r¹\r
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AuthorsListE:\rZhang Xu¹，Luo Zhen¹，Bi Jing²，Zhang Yu\r¹\r
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AuthorsHTMLE:\rZhang Xu¹，Luo Zhen¹，Bi Jing²，Zhang Yu\r¹\r
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Unit:\r\r1. 天津大学材料科学与工程学院，天津 300072；\r
\r\r2. 天津航天长征火箭制造有限公司，天津 300462\r
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Unit_EngLish:\r1. School of Materials Science and Engineering，Tianjin University，Tianjin 300072，China；
2. Tianjin Aerospace Long March Launch Vehicle Manufacturing Co.，Ltd.，Tianjin 300462，China\r
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Abstract_Chinese:\r针对TA1 工业纯钛在电阻点焊时极易与氧气发生反应而导致接头局部脆化的情况，引入了外加横向磁场以改善其电阻点焊接头的连接质量．实验使用材料为1 mm 厚的TA1 工业纯钛薄板，在220 kW 的逆变直流电阻点焊设备上进行．电极采用端部直径为6 mm 的锥形电极头．外加磁场由一对环形钕铁硼永磁铁N40 产生．上、下永磁体S 极相对，沿电极臂中心线呈轴对称安装．上、下永磁体距两试件的接触面为9 mm．以熔核尺寸和接头在拉剪测试中表现出的峰值载荷为指标，分析了外加横向磁场对TA1 工业纯钛电阻点焊连接质量的影响．并且测量了点焊接头截面的显微硬度以判断熔核边缘的氧化程度．结果表明，在同等热输入前提下，外加磁场不影响TA1 熔核内部的结晶形态，但能够有效增加熔核直径，改善TA1 点焊接头的承载能力．并且在热输入较小的条件下，外加磁场对熔核直径生长的作用更明显．当接头熔核尺寸相近时，施加外部横向磁场的点焊过程所需热输入量更小．这也导致了在同等熔核尺寸和峰值载荷前提下，有外加磁场下的点焊接头断裂模式呈现对称纽扣断裂模式，无磁场的点焊接头呈现单侧纽扣断裂模式．同时外加磁场作用下的点焊接头拉伸断口的韧窝尺寸更大，表现出更好的塑韧性，这是因为较小的热输入能降低熔核边缘区域的氧化程度．\r
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Abstract_English:\rDue to the easily oxidation of commercial pure titanium TA1 during resistance spot welding(RSW)， which leads to embrittlement of the joints，external transverse magnetic field(EMF)is introduced to improve the quality of the joint．The materials used were 1 mm thick commercial pure titanium TA1．Welding was performed using a 220 kW direct current resistance spot welding machine．Truncated-cone electrodes with a 6 mm diameter tip end was used for the welding．The EMF was generated through two identical annular N40 type NdFeB permanent magnets mounted coaxially on electrode arms with opposite polarities．The two magnets were symmetrically located with their south poles(S)against each other．The distance between permanent magnet to origin was 9 mm in this study．The effect of EMF on commercial pure titanium TA1 RSW is studied．Impacts of the EMF on the nugget size and peak load in tensile-shear tests have been systematically discussed．Besides，the microhardness of the spot welded joints was measured to determine the oxidation degree of the edge region of the nugget．The results show that the EMF doesn’t affect the crystal morphology of the joints，but improves the nugget diameter and tensile-shear peak load of the joints．Moreover，the effect of EMF on the improvement of nugget diameter is larger when the heat input is smaller．Besides，the heat-input of the RSW process with EMF is lower than its counterpart without EMF while in both situation the nugget sizes are similar to each other．The EMF can improve the plasticity of the RSW joint under the same nugget sizes and peak loads．And the joints with EMF exhibit symmetrical pull-out fracture mode and the joints without EMF exhibit unilateral pull-out fracture mode．This is because that the lower heat-input can reduce the oxidation degree of the edge region of the nugget．\r
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Keyword_Chinese:电阻点焊；外加磁场；工业纯钛；点焊质量\r

Keywords_English:resistance spot welding；external magnetic field；commercial pure titanium；spot weld quality\r


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