搅拌摩擦焊接Al-Li合金接头的微观组织及力学性能

MICROSTRUCTURES AND MECHANICAL PROPERTIES OF Al-Li ALLOY FRICTION STIR WELD

采用锥形带螺纹搅拌头搅拌摩擦焊接5 mm厚的Al-Li合金轧制板材,并对接头组织、力学性能及断裂特性进行了研究。结果表明,焊核区组织发生动态再结晶,形成细小的等轴晶晶粒,在等轴晶的晶界处析出大量的偏析相。热影响区组织发生回复和粗化反应,形成粗大的棒状回复晶粒;热机影响区组织发生弯曲变形,但整体上仍保留带状组织形貌,前进侧热机影响区组织变形程度高于后退侧,该区同时还发生回复反应,且后退侧热机影响区内的回复晶粒数量多于前进侧。拉伸实验结果表明,焊接速度v=40 mm/min时,接头强度达到最大值,为345 MPa;v=60 mm/min时,接头延伸率达到最大值,为9.6％。硬度测试结果表明,搅拌摩擦焊接头发生软化,前进侧的软化区宽度大于后退侧。断口形貌分析表明,接头断裂模式为韧-脆混合型断裂。

Friction stir welding (FSW) for 5 mm thick Al-Li alloy rolled sheet material has been completed with a cone-shape screw thread pin. The metallurgy experiment demonstrates that the dynamic recrystallization occurs in the weld nugget zone (WNZ), fine equiaxed grains form, and a large number of segregation phases appears at grain boundaries. The microstructure in the heat-affected zone (HAZ) consists of coarse bar-shdpe recovery grain, and that of the thermo-mechanically affected zone (TMAZ) exhibits bent band-like character, but the deformation degree at the advancing side is bigger than that at the retreating side. Microstructures in TMAZ are also recovered, and the amount of recovery grain at retreating side is more than that at advancing side. Tensile test shows that the joint strength and elongation are 345 MPa at welding rate v=40 mm/min, and 9.6% at v=60 mm/min respectively. Hardness measurement shows that the FSW joint is soften during welding, and the softened zone at advancing side is wider than that at retreating side. Fractographs confirm that the fracture of the joint is mixed mode of ductile and brittle fracture.