Fusion Zone Of Welded Joint Research Articles

STUDY ON MICROSTRUCTURE AND DYNAMIC FRACTURE BEHAVIOR OF Q460 STEEL WELDING JOINTS

Effects of welding heat input on the microstructure and dynamic fracture toughness (JId) of the CO2 shielded arc welded joints of Q460 high strength low alloy steel were investigated. The mechanism of effects on the dynamic facture behavior of the welded joint was also discussed. The results showed that there existed the allotriomorphic ferrite at the columnar interface in the fusion zone of welded joint under the condition of low heat input. The morphological characteristics of columnar crystal in the fusion zone gradually decreased and the allotriomorphic ferrite disappeared as the heat input increased. The fusion zone was mainly composed of acicular ferrite, and its average size increased with increasing heat input. The welded joint exhibited the optimal dynamic fracture toughness under the condition of medium heat input while it showed the lowest value under low heat input within the temperature range of -70 °C to room temperature. When the temperature decreased from room temperature to -70 °C, the dynamic fracture mechanism of Q460 welded joint changed from ductile fracture to brittle cleavage fracture. Under the condition of low heat input, the allotriomorphic ferrite characterized by the planar growth at the columnar interface in the fusion zone of welded joint can lead to the rapid intergranular crack propagation at low temperature. The fine acicular ferrite in the fusion zone of the welding joint obtained at medium heat input which *国家自然科学基金项目51371044和51571052以及中央高校基本科研业务费专项资金项目L1502027资助 收到初稿日期: 2015-12-01,收到修改稿日期: 2016-01-22 作者简介:冯祥利,男, 1972年生,博士生 DOI: 10.11900/0412.1961.2015.00617 第787-796页 pp.787-796

ＡＺ３１マグネシウム合金ＴＩＧ溶接継手の諸性質

AZ31 magnesium alloy plates 4mm in thickness were welded without addition of filler wire using a pulsed AC TIG welding machine. Microstructural observations have been carried out together with the mechanical tests on the welded joints, with the special reference to the effects of pulse frequency on the optimum welding conditions. In case of the pulse frequency of 20Hz, the crystal grains of the fusion zone are most fine. The hardness of the fusion zone of welded joints are nearly equal to that of the base metal. The welded joints without pulse have the same tensile strength and elongation as those of the base metal. The highest tensile strength and elongation of pulsed welded joints can be obtained with the pulse frequency of 20Hz, but they are inferior to those of the base metal. All the welded joints are fractured at the center of the fusion zone regardless of the pulse frequency. The bending angle of welded joints is smaller than that of the base metal. Fatigue limit of the welded joints with the pulse frequency of 20Hz is 92% of the base metal. And the fatigue limit of the pulse welded joints depends on the grain size of the fusion zone.