铝合金厚板搅拌摩擦焊焊缝疏松缺陷形成机理
收稿日期: 2016-04-26
修回日期: 2016-06-16
网络出版日期: 2016-06-22
基金资助
国家自然科学基金（51265043，51265042）；江西省高等学校科技落地计划（KJLD13055，KJLD12074）
Formation mechanism of weld loose defect in friction stir welding thick plates of aluminum alloy
Received date: 2016-04-26
Revised date: 2016-06-16
Online published: 2016-06-22
Supported by
National Natural Science Foundation of China (51265043, 51265042); Landed Plan of Science and Technology in Colleges and Universities of Jiangxi Province (KJLD13055, KJLD12074)
采用圆锥形搅拌头焊接20 mm厚的7075-T6铝板，分析焊接过程中焊缝内部疏松缺陷的形成过程及原因。研究表明，焊缝表面成形良好，无明显缺陷。但是，在焊缝轴肩区和焊核区之间出现了疏松缺陷。分析认为，焊缝上、下部金属温度差太大，导致其塑性流动行为发生变化是疏松缺陷形成的主要原因。搅拌摩擦焊（FSW）过程中，焊缝上部金属温度较高，而底部温度仍然很低，脱离搅拌针端部的塑化金属在周围冷金属巨大的变形抗力作用下转而沿搅拌针表面往上迁移。到达轴肩区下方汇聚区时，由于轴肩区金属温度高，向下的挤压力太小，导致回迁上来的塑化金属继续往上迁移并冲破轴肩区而沿轴肩边缘溢出形成飞边。汇聚区内没有足够的塑化金属填充、焊缝无法被压实而产生疏松孔洞。通过建立疏松缺陷形成的物理模型，可以更直观地反映出焊缝金属流动形态及缺陷形成过程。
毛育青 , 柯黎明 , 刘奋成 , 陈玉华 . 铝合金厚板搅拌摩擦焊焊缝疏松缺陷形成机理[J]. 航空学报, 2017 , 38(3) : 420367 -420367 . DOI: 10.7527/S1000-6893.2016.0197
20 mm thick 7075-T6 aluminum alloys are joined by friction stir welding (FSW) using a tapered pin, and the formation process and reason of loose void defect are investigated during FSW. The results show that the weld surfaces are good without any defects. However, the loose defect is found in all welds between the shoulder zone and the nugget zone. The main reason is that the metal is stirred abnormally to cause the change in the plastic flow behavior due to high temperature difference on the top and bottom of the weld. During FSW, the temperature on the top is high while low on the bottom of the weld, the plastic material fallen off the pin-tip suffers from large deformation constraining force of the surrounding cold metal, and then moves upwards along the surface of the pin to reach the shoulder zone. The extruding force to plastic material is small because the temperature is too high, and the plastic material continues to migrate upwards and traverses the shoulder zone to flow along the edge of tool shoulder and form the flash finally. There is not enough plasticized metal to fill the cavity, and the loose zone is thus formed in the weld. By establishing the physical model for loose defect formation, the flow behavior of the plastic material and the formation process of loose defect in FSW can be directly reflected.
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