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在2219-T8铝合金搅拌摩擦焊(FSW)接头焊核区(NZ)发现了局部液化现象。采用热处理和热模拟2种方法对比分析了局部液化区组织的特点,采用显微硬度计和原位拉伸实验研究了局部液化对接头力学性能的影响。结果表明,局部液化是由NZ中的Al_2Cu相与周围基体的共晶反应,即发生了组分液化所致。液化区为液相α(Al)相的半固态组织,冷却时高熔点组元a(Al)相先析出,同时在搅拌挤压和材料流动的作用下发生固液分离,形成离异共晶。液化区的硬度低于NZ正常区域,是NZ微区试样断裂的起源,降低了NZ的抗拉强度和延伸率。不过,由于液化区域是局部的、极少量的存在于NZ中,其对接头拉伸性能的影响远小于整体均发生弱化的热机械影响(TMAZ)的影响。
Local liquefaction was observed in the weld zone (NZ) of the 2219-T8 aluminum alloy friction stir welding (FSW) joint. The characteristics of the local liquefaction zone were analyzed by two methods of heat treatment and thermal simulation. The effects of the local liquefaction on the mechanical properties of the joint were studied by using microhardness tester and in-situ tensile test. The results show that the local liquefaction is caused by the eutectic reaction of the Al 2 Cu phase in NZ with the surrounding matrix. The liquefaction zone is a semi-solid structure of α (Al) phase in the liquid phase. When cooled, a (Al) phase of the high-melting point is precipitated first, and solid-liquid separation takes place under agitation and material flow to form dissociated eutectic. The hardness of the liquefied zone is lower than that of the NZ normal zone, which is the origin of the fracture of the NZ microtube and reduces the tensile strength and elongation of NZ. However, since the liquefaction zone is localized and a very small amount present in NZ, its effect on the tensile properties of the joint is much less than the effect of the weakened thermo-mechanical effect (TMAZ) as a whole.