汽车高强钢SG1000激光复合焊接力学性能研究

Laser Composite Welding Mechanical Properties for Automobile High-strength Steel SG1000

目的针对汽车高强钢SG1000焊接接头恶化等问题,研究了SG1000激光复合焊接的力学性能。方法选用等强匹配焊丝MG90-G对高强钢SG1000进行激光复合焊接,对焊接接头进行拉伸和低温冲击韧性试验,并结合扫描和硬度监测等手段对焊缝组织和断口形貌进行分析。结果由于激光的预热作用,高强钢SG1000激光复合焊接成形件的焊缝美观,焊接过程稳定可靠,焊接熔池深度较大,有效改善了传统焊接的咬边、飞溅、气孔等缺陷。焊缝组织主要由板条马氏体和奥氏体晶粒组成,热影响区的过热区内部板条马氏体和奥氏体晶粒比较粗大,而焊接母材主要为细小的板条马氏体和奥氏体晶粒。焊接拉伸断口主要为细小且较浅的韧窝,且韧窝底部存在第二相粒子及夹杂物,焊接拉伸断口断裂于热影响区且微观形貌为韧性断裂;冲击微观形貌主要由准解理小平面及河流花样组成,且存在一定数量大小不一的韧窝交错分布,焊接冲击断口断裂于热影响区且微观形貌也为韧性断裂。结论焊缝热影响区的晶粒比非热影响区的晶粒粗大,拉伸和冲击断裂均发生于热影响区;随着激光功率的增大,复合焊接接头的力学性能呈现逐渐增强的趋势;随着焊接速度的增大,复合焊接接头的力学性能呈现先增强后削弱的趋势。高强钢SG1000激光复合焊接最佳工艺参数如下:激光功率为9.5 kW,焊接速度为0.8 m/min,对应屈服强度为1072 MPa,抗拉强度为1175MPa,断裂伸长率为13.5%,冲击断裂吸收的能量为30.8J、焊缝中心显微硬度为342HV。

The work aims to address issues such as deterioration of welded joints for automobiles high-strength steel SG1000,and research the mechanical properties of SG1000 laser composite welding.Equal strength matching welding wire MG90-G was used to perform laser composite welding on high-strength steel SG1000.The welded joint was subject to tensile and low-temperature impact toughness tests.The microstructure and fracture surface of the weld were analyzed with scanning and hardness monitoring equipment.As a result,due to the preheating effect of the laser,the weld seam of the high-strength steel SG1000 laser composite welding forming part had good appearance,the welding process was stable and reliable,and the depth of the welding pool was deep,effectively mitigating defects such as undercut,spatter,and porosity in traditional welding.The weld microstructure was mainly composed of flat noodles martensite and austenite grains.The flat noodles martensite and aus-tenite grains in the overheated zone of the heat affected zone were relatively coarse,while the welding base metal was mainly fine flat noodles martensite and austenite grains,the tensile fracture of welding was mainly composed of small and shallow dim-ples,and there were anomalies such as second phase and inclusions at the bottom of the dimples,welding tensile fracture at the heat affected zone and had a microscopic morphology of ductile fracture.The impact microstructure was mainly composed of quasi cleavage small planes and river patterns,and there were a certain number of staggered distribution dimples for varying sizes,welding impact fracture at the heat affected zone and the microstructure was also ductile fracture.In conclusion,the grain size in the heat affected zone of weld is larger than that in the non heat-affected zone,and the tensile and impact fracture occurs in the heat affected zone.With the increase of laser power,the mechanical properties of composite welded joints show a gradu-ally increasing trend;With the increase of welding speed,the mechanical properties of composite welded joints show a trend of first increasing and then decreasing.The optimal process parameters for laser composite welding of high-strength steel SG1000 are laser power of 9.5 kW,welding speed of 0.8 m/min,corresponding yield strength of 1072 MPa,tensile strength of 1175 MPa,fracture elongation rate of 13.5%,energy absorbed of 30.8 J,and microhardness of the weld center of 342HV.