高转速FSW工艺特征及焊缝组织性能演变规律研究

目的研究不同转速的焊缝性能变化对组织的影响,以期为高转速搅拌摩擦焊工艺参数的优化和更大范围的应用提供指导。方法在3000~8000 r/min的高转速范围内对3A21-O态铝合金进行搅拌摩擦焊试验,焊后分析了焊缝成形特征和晶粒形态并测试了接头截面显微硬度。结果当转速由1000~4000 r/min区间升高至5000~8000 r/min区间时,焊核宽度急剧增大了近50%。这是由于焊具产热机制以滑移摩擦为主向以粘着摩擦为主转变,导致上述焊核宽度增大的行为。随着转速的增大,焊缝温度呈现出常规搅拌摩擦焊工艺中鲜见的先增大而后趋于稳定的变化趋势;温度随转速的这一演变特征导致焊缝焊核区的亚结构数量比例以及显微硬度都随转速呈现出与此相近的演变规律。结论在高转速搅拌摩擦焊中,转速提高能提高焊缝性能,且增强的焊缝性能能够在较宽的高转速区间内保持相对稳定的状态。

Process Characteristics and Weld Structure-property Evolutions of High Rotation Speed FSW

This paper aims to study the effects of weld performance changes at different rotating speeds on the micro-structure in order to provide guidance for optimization of process parameters and wider application of friction stir welding at high rotating speeds. Friction stir welding test at a high speed range of 3000-8000 r/min was carried out on 3A21-O-state aluminum alloy. The weld feature and grain morphology were analyzed and the micro-hardness of the joint was tested after welding. It was found that the nugget width was dramatically enlarged by nearly 50% as the rotation speed was increased from the range of 1000-4000 r/min to 5000-8000 r/min, which should be attributed to the change of predominant heat generation mechanism from sliding friction to sticking friction. With the increase of speed, the weld temperature increased firstly and then showed a stable change trend, which was rare in normal friction stir welding. The evolution trends of temperature with speed caused that the proportion and microhardness of substructures in nugget area showed a very similar evolvement rule. During high speed friction stir welding, the increase of rotation speed can improve the joint property. Additionally, the strengthened joint property can be maintained in a relatively large rotation speed range.