7075高强铝合金激光填丝焊接组织与力学性能研究

采用光纤激光器对4mm厚的7075铝合金进行激光填丝焊接,对焊接接头的显微组织、相结构、断口形貌、力学性能进行观察和分析。结果表明:焊缝(FZ)边缘组织为柱状枝晶组织,焊缝中心为等轴晶组织;热影响区(HAZ)保留了母材(BM)的轧制长条状形态,但晶粒有所长大。母材的相组成主要为α-Al固溶体、S-Al_2CuMg强化相和η-MgZn_2强化相,焊缝无强化相析出。焊缝区硬度值为各区中最低,热影响区显微硬度呈阶梯式增长。焊接速度为2~4m/min的接头拉伸试样均在焊缝处断裂,抗拉强度最大为母材的67.5%。接头拉伸试样均出现了颈缩现象,断口由大量的等轴状韧窝构成,为韧性断裂。

Microstructure and Mechanical Properties of Laser Welding Joints of 7075 Aluminum Alloy with Filler Wire

7075 aluminum alloy with the thickness of 4 mm was welded with filler wire by the fiber laser equipment.The microstructure,phase structure,fracture morphology and mechanical properties of welding joints were observed and analyzed.The results showed that the edge of the fusion zone (FZ) was mainly columnar dendrite grains,and the center of FZ was mainly equiaxial grains.The microstructure in the heated-affected zone (HAZ) was fibrous along the rolling direction,and the grains in the HAZ were slightly coarsened compared with those in base metal (BM).The phase of BM was mainly composed of α-Al solid solution,the precipitation of S-Al2 CuMg and η-MgZn2,but no precipitation was found in FZ.The microhardness value of FZ is the lowest in the welding joint,and a step increase of the microhardness occurred in HAZ.All of the tensile samples which were welded at welding speed from 2 m/min to 4 m/min fractured at FZ,among which the highest tensile strength was 67.5％ of BM.The necking phenomenon occurred at the welding joint of all the tensile samples,and the fracture surface was mainly composed of the equiaxed dimples,which is the typical characteristic of ductile fracture.