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利用超声波水浸聚焦入射法对1 mm厚的SUS304奥氏体不锈钢板点焊接头进行超声波C扫描成像检测,研究了不同工艺参数下获得接头的焊核直径与内部缺陷;借助于材料试验机及扫描电镜探究了接头力学性能与失效机理。结果表明:超声波C扫描能够有效地观测出点焊焊核直径,并能够甄别出焊穿、飞溅等典型焊接缺陷:当焊接电流为8 kA时,接头的平均失效载荷最大(9707.1N),而当电流增加至9 kA时,接头的平均失效载荷急剧下降到699.5N;焊接电流在4~8 kA时,接头断口处出现大小不等的韧窝,呈现出韧性断裂过程,少数试件的接头出现韧性断裂与准解理断裂过程;焊接电流为9kA时,接头主要呈现出韧性断裂与过烧沿晶断口。
Ultrasonic C-scan imaging of 1 mm-thick SUS304 austenitic stainless steel spot welded joints was carried out by ultrasonic immersion-focused method. The weld core diameter and internal defects of joints were studied under different process parameters. With the help of material testing machine and Scanning electron microscopy explores the mechanical properties of joint and failure mechanism. The results show that ultrasonic C-scan can effectively detect the diameter of spot weld nuclei and identify the typical welding defects such as welding penetration and splashing. When the welding current is 8 kA, the average failure load of the joint is the highest (9707.1N) When the current increases to 9 kA, the average failure load of the joint drops sharply to 699.5N. When the welding current is between 4 and 8 kA, dimples of unequal sizes appear at the fracture surface of the joint, showing a ductile fracture process. The ductile fracture and quasi-cleavage fracture appear. When the welding current is 9kA, the joints mainly show the fracture of ductile fracture and over-fracture along the crystal.