外加磁场对TA1工业纯钛电阻点焊连接质量的影响
|
摘要
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.
Due 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 k W 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 bothsituation 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.
Due 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 k W 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 bothsituation 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.
引文
[1]Zhang H,Senkara J.Resistance Welding:Fundamentals and Applications[M].Florida:CRC Press,2012.
[2]Watanabe Y,Takeda T,Sato H.Effect of magnetic field on weld zone by spot-welding in stainless steel[J].Transactions of the Iron&Steel Institute of Japan,2006,46(9):1292-1296.
[3]Shen Q,Li Y B,Lin Z Q,et al.Effect of external constant magnetic field on weld nugget of resistance spot welded dual-phase steel DP590[J].IEEE Transactions on Magnetics,2011,47(10):4116-4119.
[4]Yao Q,Luo Z,Li Y,et al.Effect of electromagnetic stirring on the microstructures and mechanical properties of magnesium alloy resistance spot weld[J].Materials&Design,2014,63(63):200-207.
[5]张忠典,王亚荣,李双双.外加径向恒定磁场改善高强钢点焊质量[C]//第十一次全国焊接会议论文集(第1册).上海,2005.Zhang Z,Wang Y,Li S.Effect of external radial magnetic field on high strength steel resistance spot welding[C]//Proceedings of the 11th National Welding Conference(Vol.1).Shanghai,China,2005(in Chinese).
[6]李菊,关桥,史耀武.钛合金焊接过程应力应变特点分析[J].焊接学报,2010,31(3):53-56.Li Ju,Guan Qiao,Shi Yaowu.Investigation on welding stress and strain of titanium alloy[J].Transactions of the China Welding Institution,2010,31(3):53-56(in Chinese).
[7]姚杞,李洋,罗震,等.永磁体磁场对铝合金电阻点焊力学性能及微观组织的影响[J].焊接学报,2016,37(4):52-56.Yao Qi,Li Yang,Luo Zhen,et al.Impact of external magnetic field generated by permanent magnet on mechanical property and microstructure of aluminum alloy resistance spot weld[J].Transactions of the China Welding Institution,2016,37(4):52-56(in Chinese).
[8]沈琦,李永兵,陈关龙,等.永磁体磁场对双相高强钢电阻点焊质量的影响[J].焊接学报,2011,32(4):21-24.Shen Qi,Li Yongbing,Chen Guanlong,et al.Impact of external magnetic field generated by permanent magnet on quality of dual phase high strength steel by resistance spot welding[J].Transactions of the China W e l ding Institution,2011,32(4):21-24(in Chinese).
[9]Asme M.Ultimate strength and failure mechanism of resistance spot weld subjected to tensile,shear,or combined tensile/shear loads[J].Journal of Engineering Materials&Technology,2003,125(2):125-132.
[10]Kaya Y,Kahraman N.The effects of electrode force,welding current and welding time on the resistance spot weldability of pure titanium[J].International Journal of Advanced Manufacturing Technology,2012,60(1/2/3/4):127-134.
[11]钟群鹏,赵子华.断口学[M].北京:高等教育出版社,2006.Zhong Qunpeng,Zhao Zihua.Fractography[M].Beijing:Higher Education Press,2006(in Chinese).
[2]Watanabe Y,Takeda T,Sato H.Effect of magnetic field on weld zone by spot-welding in stainless steel[J].Transactions of the Iron&Steel Institute of Japan,2006,46(9):1292-1296.
[3]Shen Q,Li Y B,Lin Z Q,et al.Effect of external constant magnetic field on weld nugget of resistance spot welded dual-phase steel DP590[J].IEEE Transactions on Magnetics,2011,47(10):4116-4119.
[4]Yao Q,Luo Z,Li Y,et al.Effect of electromagnetic stirring on the microstructures and mechanical properties of magnesium alloy resistance spot weld[J].Materials&Design,2014,63(63):200-207.
[5]张忠典,王亚荣,李双双.外加径向恒定磁场改善高强钢点焊质量[C]//第十一次全国焊接会议论文集(第1册).上海,2005.Zhang Z,Wang Y,Li S.Effect of external radial magnetic field on high strength steel resistance spot welding[C]//Proceedings of the 11th National Welding Conference(Vol.1).Shanghai,China,2005(in Chinese).
[6]李菊,关桥,史耀武.钛合金焊接过程应力应变特点分析[J].焊接学报,2010,31(3):53-56.Li Ju,Guan Qiao,Shi Yaowu.Investigation on welding stress and strain of titanium alloy[J].Transactions of the China Welding Institution,2010,31(3):53-56(in Chinese).
[7]姚杞,李洋,罗震,等.永磁体磁场对铝合金电阻点焊力学性能及微观组织的影响[J].焊接学报,2016,37(4):52-56.Yao Qi,Li Yang,Luo Zhen,et al.Impact of external magnetic field generated by permanent magnet on mechanical property and microstructure of aluminum alloy resistance spot weld[J].Transactions of the China Welding Institution,2016,37(4):52-56(in Chinese).
[8]沈琦,李永兵,陈关龙,等.永磁体磁场对双相高强钢电阻点焊质量的影响[J].焊接学报,2011,32(4):21-24.Shen Qi,Li Yongbing,Chen Guanlong,et al.Impact of external magnetic field generated by permanent magnet on quality of dual phase high strength steel by resistance spot welding[J].Transactions of the China W e l ding Institution,2011,32(4):21-24(in Chinese).
[9]Asme M.Ultimate strength and failure mechanism of resistance spot weld subjected to tensile,shear,or combined tensile/shear loads[J].Journal of Engineering Materials&Technology,2003,125(2):125-132.
[10]Kaya Y,Kahraman N.The effects of electrode force,welding current and welding time on the resistance spot weldability of pure titanium[J].International Journal of Advanced Manufacturing Technology,2012,60(1/2/3/4):127-134.
[11]钟群鹏,赵子华.断口学[M].北京:高等教育出版社,2006.Zhong Qunpeng,Zhao Zihua.Fractography[M].Beijing:Higher Education Press,2006(in Chinese).