对5mm厚5083铝合金进行FSW/MIG交叉焊接试验,分析了MIG与FSW交叉焊缝不同区域的气孔大小与分布情况,以及该交叉焊接头的力学性能.结果 表明,交叉焊缝中存在气孔缺陷,气孔多位于MIG焊道底部熔合线附近.MIG焊道与FSW热影响区交叉处的气孔较大,呈长条状.交叉焊缝显微维氏硬度并未出现明显下降,接头的平均屈服强度为147 MPa,平均抗拉强度为250.8 MPa.

对船用5083铝合金火焰矫形进行了研究,采用同步水冷降低了合金的高温停留时间.通过显微硬度、拉伸和金相试验研究了高温停留时间对5083铝合金显微组织和力学性能的影响.结果表明,矫形区域内显微硬度均低于母材,但采用同步水冷时平均硬度下降4.4 HV,而不采用水冷时显微硬度比母材下降11.6 HV;与不采用水冷的试样相比,同步水冷试样平均屈服强度上升9.16 MPa,平均抗拉强度上升1.64 MPa,但伸长率有所下降;采用同步水冷减少了晶粒长大倾向和析出相的尺寸和数量.

Aluminum alloy 5083 is widely used in the fabrication of marine vessels. This paper presents the difference in mechanical properties and microstructure between natural-cooling and water-cooling after flame straightening. Under the synchronous water-cooling process, the peak temperature of the heating center was unchanged, but the peak temperatures of the other areas decreased obviously and the cooling rate increased substantially. The microhardness of the rectified area was lower than that of the base metal. The average microhardness decreased about 4.4 HV when using synchronous water-cooling, whereas the average microhardness of the specimen without using water-cooling was 11.6 HV lower than the base metal. Tensile test results show that the yield strength and the ultimate strength of synchronous water-cooling specimen increased 9.16 MPa and 1.64 MPa on average, but the elongation rate decreased compared with the specimen only under flame straightening. The results of metallographic tests show that the grain growth tendency and precipitation phase size and quantity reduced after using synchronous water-cooling.

6082-T6 aluminum alloy plate with thickness of 42mm was butt welded by friction stir welding (FSW) from two sides. The microstructures of the joints exhibited different grain sizes because of unequal frictional heating and plastic flow during FSW process. The transition from the heat affected zone (HAZ) to the nugget zone (NZ) in thermos-mechanical affected zone of advancing side (AS-TMAZ) was more sudden than thermos-mechanical affected zone of retreating side (RS-TMAZ). Kissing bond (KB) defect throughout the entire FSW joint was displayed both at the grain boundary and in the interior of the grain with semi-continuous bands. KB had no direct effect on tensile properties. Vickers hardness of the FSW joint was lower than the BM because its high heat input, dissolved and coarsened precipitates and little to the grain size after FSW. Hardness distribution of double-sided welding joint showed X-shaped area softening characteristics, that is to say the lowest hardness was the junction of two welding joint of NZ and the junction of TMAZ and HAZ. The tensile fracture position occurred in the lowest hardness region of the FSW joint, and it did not occur in the KB defect position.

The tunnel defect formed in friction stir weld would dramatically push the mechanical properties of joints into deterioration. In this study, friction stir welding process was adopted to repair the joints of 7N01 aluminum alloy with tunnel defect. The effects of friction stir repair welding process on the microstructure and mechanical properties were comprehensively investigated. Microstructure of the repaired joints shows that the grain size in nugget zone decreases slightly while the recrystallization in the retreating side of thermo-mechanically affected zone is intensified as the joints are repaired. The microhardness of the repaired joints declined slightly compared with the defective joint. However, the yield strength and tensile strength increase and recover to the values of the joints free of defect. The longitudinal residual stress in weld zone increased remarkably as the repair times increase. Compared with the once repaired joint, yield strength and tensile strength of the twice repaired joint reduced slightly, and the throat thickness also reduced during the repeated repair welding process. Therefore, the times of repair welding applied should be limited actually.