The dissimilar metals of Ti6Al4V titanium alloy and 2A12 aluminum alloy were joined by pinless friction stir lap spot welding. After welding, the low melting point aluminum alloy was melted by friction heat. The high melting point titanium alloy remained solid during the welding process and interacted with the aluminum alloy in the liquid state. Finally, at the Ti/Al interface formed a welded joint, and the tensile shear force of the joint reaches 19.20 kN. This paper studied the microstructure changes of the titanium alloy and aluminum alloy, and the characteristic morphology of the joint interface. The results indicate that due to the influence of friction heat and the downward pressure of the stirring head, the structures of the titanium alloy and aluminum alloy at the welding point changed significantly. On the titanium side mainly formed the thermal mechanically affected zone and the base material zone. Three areas formed on the aluminum side:the nugget zone, heat-affected zone, and base material zone. The grain size of heat-affected zone and nugget zone was larger than that of the base material zone, and its structure underwent a process from being heated for a long time to melt to complete melting. A uniform, dense and thin intermetallic compound layer formed at the interface of the lap joint, with the main component being TiAl3. The interface area of the joint changed obviously. There was a uniform interface layer in the middle part, and the layer gradually disappeared as it extended to both sides of the joint with the gathering of Cu at the edge. Compared with that by other Ti/Al lap joint welding methods, the tensile and shear strength of the joint obtained by pinless friction stir spot welding has been significantly improved.
[1] CHEN Y H, NI Q, KE L M. Interface characteristic of friction stir welding lap joints of Ti/Al dissimilar alloys[J].Transactions of Nonferrous Metals Society of China, 2012, 22(2):299-304.
[2] 黄永宪, 吕宗亮, 万龙, 等. 钛/铝异质金属搅拌摩擦焊技术研究进展[J].航空学报, 2018, 39(11):022154. HUANG Y X, LYU Z L, WAN L, et al. Review of dissimilar friction stir welding between titanium and aluminum[J].Acta Aeronautica et Astronautica Sinica, 2018, 39(11):022154(in Chinese).
[3] 张鑫, 陈玉华, 王善林. 中间层材料对Ti/Al搅拌摩擦焊接头组织和性能的影响[J].稀有金属材料与工程, 2016, 45(5):1290-1295. ZHANG X, CHEN Y H, WANG S L. Effect of intermediate layer on microstructure and mechanical properties of Ti/Al joint welded by friction stir welding[J].Rare Metal Materials and Engineering, 2016, 45(5):1290-1295(in Chinese).
[4] ZENG H, LUO G Q, SHEN Q, et al. Preparation of TC4-LY12 joint by vacuum diffusion welding[J].Advanced Materials Research, 2009, 66:242-245.
[5] MOLLER F, GRDEN M, THOMY C, et al. Combined lase hybrid structures[J].Physic Procedia, 2011, 12:215-223.
[6] HUANG Y X, LV Z L, WAN L, et al. A new method of hybrid friction stir welding assisted by friction surfacing for joining dissimilar Ti/Al alloy[J].Materials Letters, 2017, 207:172-175.
[7] WU A P, SONG Z H, NAKATA K, et al. Interface and properties of the friction stir welded joints of titanium alloy Ti6Al4V with aluminum alloy 6061[J].Materials & Design, 2015, 71:85-92.
[8] LI Y, ZHANG Y, LUO Z. Microstructure and mechanical properties of Al/Ti joints welded by resistance spot welding[J].Science and Technology of Welding and Joining, 2015, 20(5):385-394.
[9] YANG X W, FENG W Y, LI W Y, et al. Microstructure and mechanical properties of dissimilar pinless friction stir spot welded 2A12 aluminum alloy and TC4 titanium alloy joints[J].Journal of Central South University, 2018, 25(12):3075-3084.
[10] PLAINE A H, SUHUDDIN U F H, AFONSO C R M, et al. Interface formation and properties of friction spot welded joints of AA5754 and Ti6Al4V alloys[J].Materials & Design, 2016, 93:224-231.
[11] 张志涛. Ti/Al异种金属搅拌摩擦焊点焊工艺及组织性能研究[D]. 南昌:南昌航空大学, 2017. ZHANG Z T. Study on the parameters and microstructure properties of Ti/Al friction stir spot welded joints[D]. Nanchang:Nanchang Hangkong University, 2017(in Chinese).
[12] CHEN Z W, YAZDANIAN S. Microstructures in interface region and mechanical behaviours of friction stir lap Al6060 to Ti-6Al-4V welds[J].Materials Science and Engineering:A, 2015, 634:37-45.
[13] 曹文明. Ti/Al搅拌摩擦点焊-钎焊复合焊接接头组织性能研究[D]. 南昌:南昌航空大学, 2017. CAO W M. Study on microstructure and properties of friction stir spot welding-soldering hybrid weled joint between titanium and aluminum dissimilar metals[D]. Nanchang:Nanchang Hangkong University, 2017(in Chinese).
[14] 刘东亚. Ti/Al异种金属电阻点焊工艺及接头形成机理研究[D]. 南昌:南昌航空大学, 2016. LIU D Y. Study on Ti/Al dissimilar metal resistance spot welding technique and joint formation mechanism[D]. Nanchang:Nanchang Hangkong University, 2016(in Chinese).
[15] ZHOU L, MIN J, HE W X, et al. Effect of welding time on microstructure and mechanical properties of Al-Ti ultrasonic spot welds[J].Journal of Manufacturing Processes, 2018, 33:64-73.
[16] VAN DER REST C, JACQUES P J, DE SIMAR A. On the joining of steel and aluminium by means of a new friction melt bonding process[J].Scripta Materialia, 2014, 77:25-28.
[17] KUANG B B, SHEN Y F, CHEN W H, et al. The dissimilar friction stir lap welding of 1A99 Al to pure Cu using Zn as filler metal with "pinless" tool configuration[J].Materials & Design, 2015, 68:54-62.
[18] 闫泰起, 程序, 李安, 等. 轧制+增材TC4合金电子束焊接接头组织与性能[J].焊接学报, 2019, 40(6):112-117, 166. YAN T Q, CHENG X, LI A, et al. Microstructure and mechanical properties of electron beam welded joints in different state of TC4[J].Transactions of the China Welding Institution, 2019, 40(6):112-117, 166(in Chinese).
[19] 许鸿吉, 尹丽香, 李晋炜, 等. TC4钛合金电子束焊接接头组织和性能[J].焊接学报, 2005, 26(11):43-46, 3. XU H J, YIN L X, LI J W, et al. Microstructures and properties of TC4 alloy joints welded by the electron beam welding[J].Transactions of the China Welding Institution, 2005, 26(11):43-46, 3(in Chinese).
[20] KATSAS S, NIKOLAOU J, PAPADIMITRIOU G. Corrosion resistance of repair welded naval aluminium alloys[J].Materials & Design, 2007, 28(3):831-836.
[21] REN J W, LI Y J, FENG T. Microstructure characteristics in the interface zone of Ti/Al diffusion bonding[J].Materials Letters, 2002, 56(5):647-652.
[22] CHEN Y H, DENG H B, LIU H, et al. A novel strategy for the reliable joining of Ti6Al4V/2A12-T4 dissimilar alloys via friction melt-bonded spot welding[J].Materials Letters, 2019, 253:306-309.
[23] 顾华. 2A12厚板铝合金电子束焊接接头组织及工艺研究[D]. 哈尔滨:哈尔滨工业大学, 2017. GU H. Research on the microstructure and process of thick 2A12 aluminum alloy electron beam welded joints[D]. Harbin:Harbin Institute of Technology, 2017(in Chinese).
[24] ZHANG C Q, ROBSON J D, PRANGNELL P B. Dissimilar ultrasonic spot welding of aerospace aluminum alloy AA2139 to titanium alloy TiAl6V4[J].Journal of Materials Processing Technology, 2016, 231:382-388.
[25] SUN Q J, LI J Z, LIU Y B, et al. Microstructural characterization and mechanical properties of Al/Ti joint welded by CMT method-Assisted hybrid magnetic field[J].Materials & Design, 2017, 116:316-324.
[26] ZHAO H Y, YU M R, JIANG Z H, et al. Interfacial microstructure and mechanical properties of Al/Ti dissimilar joints fabricated via friction stir welding[J].Journal of Alloys and Compounds, 2019, 789:139-149.
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