铝合金薄板高转速搅拌摩擦焊接头组织与力学性能

Microstructures and Mechanical Properties of Thin Plate Aluminium Alloy Joint Prepared by High Rotational Speed Friction Stir Welding

采用高转速微型搅拌摩擦焊接工艺实现了0.8 mm厚6061-T6铝合金薄板对接。利用OM、SEM、TEM及EBSD等测试技术探讨了高转速对接头微观组织及力学性能的影响规律。结果表明,高转速焊接6061-T6薄板时,焊缝表面成型良好,焊缝各区域组织呈连续均匀过渡。与常规搅拌摩擦焊相比,高转速工艺下,焊缝区b-Mg2Si、S相(Al2Cu Mg)和Al8Fe2Si析出相数量增多,特别是长条状b-Mg_2Si数量增多,焊缝区显微硬度值明显提升;转速8000 r/min、焊速1500 mm/min条件下,接头最大抗拉强度高达301.8 MPa,是母材抗拉强度(351.7 MPa)的85.8%;转速对6061-T6铝合金超薄板高转速搅拌摩擦焊对接接头抗拉强度影响较小,接头断裂模式为脆性断裂为主的韧-脆混合断裂。

Aluminium alloys were widely applied in rail transit, ships and aerospace owing to their unique properties, such as low density, high strength and stiffness, outstanding corrosion resistance and low temperature performance. As a type of structure material, aluminium alloy joining was inevitable.However, these alloys were often considered very difficult to weld using traditional fusion welding technique since the welding seams were often accompanied with metallurgical defects, large deformation and stress. Friction stir welding （FSW）, an innovative solid-state welding technology invented at the welding institute （TWI）, was seen by designers as an effective joining methods in welding aluminium alloys due to low heat input, small stress-strain and environment friendly. In this work, 0.8 mm thick plate of 6061-T6 aluminium alloy was successfully welded by use of high rotational speed fiction stir welding technology. The microstructure and mechanical property of the butt joints prepared by high rotational speed friction stir welding were analysed in detail. The results show that the well surface topography and excellent bonding interface existed in the nugget zone （NZ） were observed. Both of the microhardness of the weld seam was lower than that of the substrate. The lowest microhardness of the butt joints located between the thermo-mechanically affected zone （TMAZ） and heat affected zone （HAZ）. Compared with the conventional rotational speed, the number of β-Mg2Si, Al2CuMg and Al2Fe2Si precipitated phases existed in the NZ was more, which made the microhardness in the NZ improved significantly. The rod-shaped precipitates （Mg2Si） have the greatest influence on the microhardness. The excellent mechanical properties were obtained at the rotational speed of 8000 r/min and welding speed of 1500 mm/min. The maximum tensile strength was 301.8 MPa, which was 85.8% of the as-received 6061-T6 （351.7 MPa）. And the toughness-brittleness fracture mode appeared.