0.02 mm thick Cu foil was used as tracer material when 7075-T6 aluminum alloy thick plates with a thickness of 20 mm were friction stir welded using the tool with a triangle plane tapered pin .The vertical temperature distribution was measured and the distribution of tracer material in the weld seam was observed ,and the plastic flow characteristic of the local material was analyzed .The results show that the peak temperature decreases gradually along the vertically downward direction of the weld seam , and the temperature difference between the top and the root is about 90 ℃ .Also ,the temperature on the advancing side (AS) is 15℃ higher than that on the retreating side (RS) for two symmetric points at the same thickness of the weld .Moreover ,on the weld top the Cu foil is broken up into small particles and distributed in the nugget zone (NZ) ,while Cu with flake structure is presented on the weld root of the NZ on the AS .It is interesting that the NZ consists of many onion rings ,and in NZ the metal shows textured structure ,which might be ascribed to the change of material flow along the vertical direction of the weld seam .%以0.02 mm厚铜箔为标示材料,采用带三角平面圆锥形搅拌针对20 mm厚7075-T6铝板进行焊接.通过测试沿焊缝厚度方向上温度场分布及观察标示材料分布状态,分析焊缝局部金属塑性流动行为特征.结果表明,沿焊缝厚度方向上自上而下的金属温度逐渐降低;焊缝上、下表面温度差约为90℃;同一厚度上相对称的两点,位于前进边金属的温度高于返回边约15℃.位于焊核区上部的铜箔呈细小颗粒状均匀分布;下部铜箔则呈层片状分布,且向前进边偏移.焊核区由多个呈纹路状、有序排列的洋葱环结构相互层叠而成,这与焊缝塑化金属沿轴向迁移方式发生变化有关.
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