摩擦攪拌點銲(FSSW)為摩擦攪拌銲接(FSW)的擴充應用，其為一固態接合技術，由於過程中溫度未達熔點，故無氣孔、凝固裂紋等傳統熔融銲接所產生之缺陷，所以特別適合鎂、鋁合金等輕金屬點銲的應用。
實驗結果發現暫態拘束空間(Constraint space)之建立，為形成攪拌區及銲件接合行為的必要條件。摩擦攪拌點銲期間，除工具的攪拌作用(Traction force)直接造成材料的塑性流動外，由於攪拌工具幾何形狀在拘束空間內造成的壓力梯度(孔隙效應)更是引發材料軸向或徑向流動及形成攪拌區的關鍵因素，而攪拌區的形成及成長將影響板材的接合行為及上板材厚度減少的趨勢，進而影響銲件之機械性質。因此適當的攪拌工具設計將可大大提升銲件的接合效能。而適當的製程參數也是形成良好銲件的必要條件。三角柱凸銷及螺紋圓柱凸銷以不同的塑性流動機制形成攪拌區，螺紋圓柱凸銷驅動材料軸向流動的效應高於光滑三角柱凸銷；但三角柱的凸銷其驅動材料徑向(Radial direction)流動的效應，則高於螺紋圓柱凸銷。因此兩者的銲件具有十分不同的銲道形貌。由於Hook幾何形狀的差異，其拉剪破壞模式及強度也明顯不同。螺紋圓柱凸銷製程之銲件其拉剪強度略高於三角柱製程之銲件。
本文建立不同幾何形狀的工具之摩擦攪拌點銲(FSSW)材料流動的模式，並藉由追蹤物(tracer)技術及實驗觀察來闡述攪拌工具的肩部及凸銷之幾何形狀對材料塑性流動及板材接合的效應，並提出攪拌區(SZ)形成機制，以及銲接參數對銲件破壞模式及接合強度之效應的論述，期能對FSSW的工具設計提供參考。

Friction stir spot welding (FSSW) is a derivative process of the friction stir welding (FSW), which is a solid-state joining technique, due to the process temperature below the melting point, so it therefore does not exit porosity, solidification cracking and other defects generated by traditional fusion welding. It is especially suitable for magnesium, aluminum and other light metal alloys.
Results showed that, the construction of the transient constrained space is a prerequisite to the formation of a stirring area and the bonding of the welding work pieces. Friction stir spot welding (FSSW) is driven mainly by the materials flow induced by the stirring tool in a constrained space that gradually diminishes the contact interface between the upper and lower plates leaving them bonded to each other. The stirring tool has a decisive influence on the flowing behavior of the plastic and the bonding strength of the welding work pieces.
During the FSSW period, except for the traction force of the tool that can directly cause the flow of plastic materials, the pressure gradient generated in the constrained space by the tool geometry that causes the axial or radial flow of the materials and the formation of a stir zone are even more key factors. The formation and growth of the stir zone will influence the bonding behavior of the plates and the effective thickness reduction trend of the upper plate. This will further influence the mechanical strength of the welding work pieces. Therefore, the appropriate design of the stirring tool can greatly improve the bonding performance of the welding work pieces. In addition, appropriate process parameters are also a prerequisite to the formation of well-welded work pieces.
The triangular tool pin and the threaded cylindrical tool pin will form stir zone caused by the different plastic flow mechanisms. The threaded cylindrical tool pin has a higher performance than the smooth triangular tool pin when driving the axial flow of materials. However, the triangular tool pin has a higher performance than the threaded cylindrical tool pin when driving the radial flow. Therefore, the nuggets of welding working pieces of the two types are totally different in their geometric features. Because of the geometrical differences of the hook, its tensile shear failure modes and strength also have significant differences. The welding work pieces made by the process using the threaded cylindrical tool pin has a slightly higher tensile and shear strengths than those made by the process using the triangular tool pin.
This study established the FSSW materials flow modes using different geometrical tools as well as observations from the experiments. It has also used tracer techniques to elaborate on the influences on the flow of materials and the bonding effect of the plates induced by the shoulder of the stirring tool and the geometrical shapes of the tool pin. The formation mechanism of the stirring zone was presented and the effects of the welding parameters on the welding work piece failure modes and their bonding strength were also discussed. This was done in the hope of providing more useful references for the FSSW tool design.

1.Thomas, W. M., Nicholas, E. D., “Friction stir welding for the transportation industries”, Materials and Design, Vol. 18, No. 4/6, pp. 269-273 (1997).
2.Fonda, R. W., Bingert, J. F., Colligan, K. J., “Development of grain structure during friction stir welding”, Sripta Materialia, Vol. 51, pp. 243-248 (2004).
3.Deqing, W., Shuhuadr, L., “Study of friction stir welding of aluminum”, Journal of Materials Science, Vol. 39, pp. 1689-1693 (2004).
4.Mishra, R. S., Ma, Z. Y., “Friction stir welding and processing”, Materials Science and Engineering: R, Vol. R50, pp. 1–78 (2005).
5.Lu G., Williams, J. C., “Titanium”, Springer, NY, pp. 109–113 (2007).
6.Sato, Y. S, Yamanoi, H., Kokawa, H. and Furuhara, T. “Microstructural evolution of ultrahigh carbon steel during friction stir welding”, Scripta Materialia, 57,557–560 (2007).
7.Feng, Z., Santella, M. L., and David, S. A., “Friction Stir Spot Welding of Advanced High-Strength Steels–A Feasibility Study”, SAE Technical Paper, No 2005-01-1248.
8.Shindo, D. J., Rivera, A. R. and Murr, L. E., “Shape Optimization for tool wear in the Friction-Stir Welding of Cast Al 358-20% SiC”, Journal of Materials Science, Vol. 37, pp. 4999–5005, (2002).
9.Uzun, H., “Friction stir welding of SiC particulate reinforced AA2124 aluminium alloy matrix composite “, Materials and Design, 28, 1440–1446 (2007).
10.Lee, C.J., Huang, J.C. and Hsieh, P.J., “Mg based nano-composites fabricated by friction stir processing”, Scripta Materialia, 54, pp. 1415–1420 (2006)
11.Rhodes, C. G., Mahoney, M. W., Bingel, W. H., Spurling, R. A., and Bampton, C. C., “Effects of Friction Stir Welding on Microstructure of 7075 Aluminum”, Scripta Mater., Vol. 36, pp.69–73 (1997).
12.Liu, G., Murr, L. E., Niou, C. S., McClure, J. C., and Vega, F. R., “Microstructural Aspects of the Friction-Stir Welding of 6061-T6 Aluminum”, Scripta Mater.,Vol. 37, pp. 355–359 (1997).
13.Li, Y., Murr, L. E., and McClure, J. C., “Flow Visualization, Residual Microstructures Associated with the Friction-Stir Welding of 2024 Aluminumto 6061 Aluminum”, Materials Science and Engineering, A271, pp. 213–223 (1999).
14.Ma, Z. Y., “Friction Stir Processing Technology: A Review”, Metallurgical and materials transactions A, Vol. 39A, pp. 642-658 (2008).
15.Joel, J. D., "The Friction Stir Welding advantage" , Welding Journal, Vol. 80, No. 5, pp. 269-273 (2001).
16.Hwan, S., Park, C., Sato, Y. S. and Kokawa, H., “Microstructural evolution and its effect on Hall-Petch relationship in friction stir welding of thixomolded Mg alloy AZ91D”, Journal of Materials Science, 38, pp. 4379 – 4383 (2003)
17.Murr, L.E., Pizana, C., “Dynamic Recrystallization: The Dynamic Deformation Regime”, Metallurgical and Materials Transactions A, 38A, pp. 2611–2628 (2007).
18.Sakano, R., Murakami, K., Yamashita, K., Hyoe, T., Fuzimoto, M., Inuzuka, M., Nagao, Y., Kashiki, H., “Development of spot FSW robot system for automobile body members”, In: Proceedings of the 3rd International Symposium of Friction Stir Welding, Kobe, Japan, September, pp. 27–28 (2001).
19.Schilling, C., Dos Santos, J., “Method and device for joining at least two adjoining work pieces by friction welding”, US Patent 0179682 (2002).
20.日本川崎重工業(株) : http://www.khi.co.jp/robot/.
21.藤本光生，古賀信次，阿部奈津美，佐藤裕，粉川博之，” 摩擦攪拌点接合で得られたアルミニウム合金継手における塑性流動に関する検討 “，日本溶接学会論文集，第26巻，第3号， pp. 67-73 (2008).
22.Wang, D. A., Lee, S. C., “Microstructures and failure mechanisms of friction stir spot welds of aluminum 6061-T6 sheets”, Journal of Materials Processing Technology, Vol. 186, pp. 291–297 (2007).
23.Fujimoto, M., Koga, S., Abe, N., Sato, S. Y. and Kokawa H., ”Microstructural Analysis of the Stir Zone of Al Alloy Produced by Friction Stir Spot Welding”,日本溶接学会論文集, Vol. 25, No.4, pp. 553-559 (2007).
24.Nandan, R., DebRoy, T., “Recent advances in friction-stir welding Process, weldment structure and properties”, Progress in Materials Science, 53, pp. 980–1023 (2008).
25.Horie, S., Shinozaki, K., Yamamoto, M., Kadoi, K. and North, T.H., “Effects of tool geometry and process conditions on material flow and strength of friction stir spot welded joint”, 日本溶接學會論文集, Vol. 29, No. 3, pp. 119s-123s (2011).
26.Badarinarayan, H., Yang, Q. and Zhu, S., “Effect of tool geometry on static strength of friction stir spot-welded aluminum alloy”, International Journal of Machine Tools & Manufacture, 49, pp. 142–148 (2009).
27.Yin, Y. H., Sun, N., North, T. H. and Hu, S.S., “Microstructures and mechanical properties in dissimilar AZ91/AZ31 spot welds”, Materials Characterization, 6 1, pp. 1018-1028 (2010).
28.Su, P., Gerlich, A., North, T. H., and Bendzsak, G. J., “Intermixing in Dissimilar Friction Stir Spot Welds”, Metallurgical and materials transactions A, Vol 38a, March, pp. 584-595 (2007).
29.Rosendo, T., Parra, B., Tier, M. A. D., da Silva, A. A. M. , dos Santos, J. F., Strohaecker, T. R. and Alcântara N. G., “Mechanical and microstructural investigation of friction spot welded AA6181-T4 aluminium alloy”, Materials and Design, 32, pp. 1094–1100 (2011).
30.Yuana, W., Mishra, R., Webb, S. S., Chen, Y. L, Carlson, B., Herling, D. R. and Grant, G. J., “Effect of tool design and process parameters on properties of Al alloy 6016 friction stir spot welds”, Journal of Materials Processing Technology, 211, pp. 972–977 (2011).
31.Bakavos, D., Chen, Y., Babout, L. and Prangnell, P., “Material interactions in a novel pinless tool approach to friction stir spot welding thin aluminum sheet”, Metallurgical and materials transactions A, Vol 42A, pp. 1266-1282 (2011).
32.Tozakia, Y., Uematsub, Y. and Tokaji, K., “Effect of tool geometry on microstructure and static strength in friction stir spot welded aluminium alloys”, International Journal of Machine Tools & Manufacture, 47, pp. 2230–2236 (2007).
33.Yin, Y. H., Sun, N, North, T. H. and Hu S. S., “Hook formation and mechanical properties in AZ31 friction stir spot welds”, Journal of Materials Processing Technology, 210, pp. 2062–2070 (2010).
34.Fujimoto, M., Koga, S., Abe, N., Sato, S. Y. and Kokawa, H., “Analysis of plastic flow of the Al alloy joint produced by friction stir spot welding”, Welding International, Vol. 23, No. 8, 589-596 (2009).
35.Fujimoto, M., Watanabe, Abe, D., N., Yutaka, S. S. and Kokawa, H., “Effects of process time and thread on tensile shear strength of Al alloy lap joint produced by friction stir spot welding”, Welding International., Vol. 24, No.3, March, pp. 169-175 (2010).
36.Fatini, L., Barcellona, A., Buffa, G. and Palmeri, D., “Friction stir spot welding of AA6082-T6: influence of the most relevant process parameters and comparison with classic mechanical fastening techniques”, Journal of Engineering Manufacture, Vol. 221 part B, pp. 1111-1118 (2007).
37.Yuana, W., Mishra, R., Webb, S. S., Chen, Y. L, Carlson, B., Herling, D. R. and Grant, G. J., “Effect of tool design and process parameters on properties of Al alloy 6016 friction stir spot welds”, Journal of Materials Processing Technology, 211, pp. 972–977 (2011).
38.Bakavos, D., Chen, Y., Babout, L. and Prangnell, P., “Material interactions in a novel pinless tool approach to friction stir spot welding thin aluminum sheet”, Metallurgical and materials transactions A, Vol 42A, pp. 1266-1282 (2011).
39.Tozaki, Y., Uematsu, Y. and Tokaji, K., “A newly developed tool without probe for friction stir spot welding and its performance”, Journal of Materials Processing Technology, 210, pp. 844–851 (2010).
40.Arul, S. G., Miller, S. F., Kruger, G. H., Pan, T. Y., Mallick, P. K. and Shih, A. J., “Experimental study of joint performance in spot friction welding of 6111-T4 aluminium alloy”, Science and Technology of Welding and Joining, Vol. 13, No. 7, pp. 629-937 (2008).
41.Bozzi, S., Helbert-Ettera, A. L., Baudin, T., Klosek, V., Kerbiguet, J. G. and Criqui, B., “Influence of FSSW parameters on fracture mechanisms of 5182 aluminum welds”, Journal of Materials Processing Technology , 210, pp. 1429–1435 (2010).
42.Horie, S., Yamamoto, M., Shinozaki, K., North, T. H., Kadoi, K., Gerlich, A., Shibayanagi, T., “Local Melting and Cracking during Friction Stir Spot welding on Mg-Al binary alloy”, 日本溶接學會論文集, 第27卷第2號，pp. 94s-98s (2009).
43.刘克文, 邢丽, 柯黎明, “LY12铝合金摩擦搅拌点焊接组织及性能”, The Chinese Journal of Nonferrous Metals, 第18卷,第2期, pp. 288-293 (2008).
44.Lathabai, S., Painter, M. J., Cantin, G. M. D. and Tyagi, V. K., “Friction spot joining of an extruded Al–Mg–Si alloy”, Scripta Materialia, 55, pp. 899–902 (2006).
45.Lin, Y. C., Liu, J. J., Lin, B. Y., Lin, C. M. and Tsai, H. L., ”Effects of process parameters on strength of Mg alloy AZ61 friction stir spot welds”, Materials and Design, 35, pp. 350–357 (2012).
46.Tozaki, Y., Uematsu, Y. and Tokaji, K.,“Effect of processing parameters on static strength of dissimilar friction stir spot welds between different aluminium alloys”, Fatigue and Fracture Engineering Materials and Structures, 30 , pp. 143–148 (2007).
47.Sato, S. Y., Fujimoto, M., Abe, N. and Kokawa, H., ”Friction stir spot welding phenomena in Al alloy 6061”, Materials Science Forum , Vol.638-642, pp. 1243-1248 (2009).
48.Uematsu, Y., Tokaji, K., Tozaki, Y., Kurita, T. and Murata, S., “Effect of post heat treatment on fatigue behavior of friction stir spot welded Al-Mg-Si alloy”, 溶接學會論文集 第26卷第1號, pp. 7-14 (2009).
49.Horie, S., Shinozaki, K., Yamamoto, M. and North, T. H., “Experimental investigation of material flow during friction stir spot welding”, Science and Technology of Welding and Joining, Vol. 15, No. 8, pp. 667-670 (2010).
50.Hirasawa, S., Badarinarayan, H., Okamoto, K., Tomimura, T. and Kawanami, T., “Analysis of effect of tool geometry on plastic flow during friction stir spot welding using particle method”, Journal of Materials Processing Technology, 210, pp. 1455–1463 (2010).
51.Yang, Q., Mironov, S., Sato, Y. S. and Okamoto, K., “Material flow during friction stir spot welding”, Materials Science and Engineering A, 527, pp. 4389–4398 (2010).
52.Merzoug, M., Mazari, M., Berrahal, L. and Imad, A., “Parametric studies of the process of friction spot stir welding of aluminium 6060-T5 alloys”, Materials and Design, 31, pp. 3023–3028 (2010).
53.Gerlich, A., Su, P., Yamamoto, M., North, T. H., “Effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy”, Journal of Materials Science, 42, pp. 5589–5601 (2007).
54.Zhang, Z., Yang, X., Zhang, J., Zhou, G., Xu, X., Zou, B., “Effect of welding parameters on microstructure and mechanical properties of friction stir spot welded 5052 aluminum alloy”, Materials and Design , 32, pp. 4461–4470 (2011).
55.Wang, D. A., Lee, S.C., “Microstructures and failure mechanisms of friction stir spot welds of aluminum 6061-T6 sheets”, Journal of Materials Processing Technolog, 186, pp. 291–297 (2007).
56.Shibayanagi, T., Gerlich, A., Kashihara K., and Thomas N., “Textures in Single-Crystal Aluminum Friction Stir Spot Welds”, Metallurgical and materials transactions A, Vol. 40A, April, pp. 920-931 (2009).
57.Badarinarayan, H., Shi, Y., Li, X. and Okamoto, K., “Effect of tool geometry on hook formation and static strength of friction stir spot welded aluminum 5754-O sheets”, International Journal of Machine Tools & Manufacture, 49, pp. 814–823 (2009).
58.Yin, Y. H., Ikuta, A. and North, T. H., “Microstructural features and mechanical properties of AM60 and AZ31 friction stir spot weld”, Materials and Design, 31, pp. 4764–4776 (2010).