In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four me...In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.展开更多
Microstructures and mechanical properties of Nd ： YAG laser welded transformation induced plasticity （TRIP） steel with tensile strength of 645 MPa were studied. Due to high cooling speed of laser welding, the weld ...Microstructures and mechanical properties of Nd ： YAG laser welded transformation induced plasticity （TRIP） steel with tensile strength of 645 MPa were studied. Due to high cooling speed of laser welding, the weld metal mainly consists of martensite different from the base metal, which is composed of ferrite matrix with bainite and a little retained austenite. Therefore, the weld metal has maximum hardness at welded joint. The yield strength and tensile strength of welded specimens tested perpendicular to weld line were almost equal to those of the base metal. But the yield strength and tensile strength of welded specimens tested parallel with weld line were a little higher than those of the base metal. The formability of laser welded TRIP steel was decreased compared with that of the base metal.展开更多
Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructura...Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.展开更多
Laser shock peening（LSP） is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP p...Laser shock peening（LSP） is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP process.A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer.Assuming a linearly gradient distribution of impact toughness,the parameters controlling the impact toughness of the gradient hardened layer were given.The influence of laser power densities and the number of laser shots on the impact toughness were investigated.The impact toughness of the laser peened layer improves compared with an untreated specimen,and the impact toughness increases with the laser power densities and decreases with the number of laser shots.Through the fracture morphology analysis by a scanning electron microscope,we established that the Cr5Mo1 V steel was fractured by the cleavage fracture mechanism combined with a few dimples.The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.展开更多
The effects of YAG laser welding conditions on mechanical properties andpress formability (bendability, stretch-formability and deep drawability) of high-strengthtransformation-induced plasticity-aided dual-phase (TDP...The effects of YAG laser welding conditions on mechanical properties andpress formability (bendability, stretch-formability and deep drawability) of high-strengthtransformation-induced plasticity-aided dual-phase (TDP) steel were investigated. Tensile tests andpress forming tests have been conducted for laser butt welded joints between two pieces of the samesteel. The tensile property and press formability were affected by the welding speed of 100 to1100mm/min and the energy of 6 to 9J/pulse. Excellent press formability was obtained with the energyof 6J/pulse and the welding speed of 300mm/min. It was concluded that the excellent weldability ofthe TDP steel can be ascribed to the weld joint formation.展开更多
为了研究20 W纳秒激光对碳纤维复合材料(CFRP)烧蚀的工艺质量,采用单因素实验方法及光切法进行了理论分析和实验验证,得到了扫描速率、峰值功率、离焦量对材料表面加工质量的影响规律,并对0.5 mm CFRP材料板进行了烧蚀实验。结果表明,...为了研究20 W纳秒激光对碳纤维复合材料(CFRP)烧蚀的工艺质量,采用单因素实验方法及光切法进行了理论分析和实验验证,得到了扫描速率、峰值功率、离焦量对材料表面加工质量的影响规律,并对0.5 mm CFRP材料板进行了烧蚀实验。结果表明,调整激光器的离焦量,让激光的焦点与材料平面在同一高度,可使扫描线宽最小,减少了材料烧蚀的热影响区,提高了激光能量利用率;设定激光扫描速率为220 mm/s和峰值功率为10 W,可得到大小为3.50μm的CFRP最小表面粗糙度平均值,其中粗糙度数据稳定性样本方差最佳,约为0.133μm 2,在此条件下可得到良好的加工表现。此研究为脉冲激光加工CFRP材料工艺研究提供一定参考,并为脉冲激光加工复合材料工艺应用打下了一定的实践基础。展开更多
基金Supported by the National Key R&D Program of China under Grant No 2016YFA0401100the National Natural Science Foundation of China under Grant No 61575129the National High-Technology Research and Development Program of China under Grant No 2015AA021102
文摘In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.
文摘Microstructures and mechanical properties of Nd ： YAG laser welded transformation induced plasticity （TRIP） steel with tensile strength of 645 MPa were studied. Due to high cooling speed of laser welding, the weld metal mainly consists of martensite different from the base metal, which is composed of ferrite matrix with bainite and a little retained austenite. Therefore, the weld metal has maximum hardness at welded joint. The yield strength and tensile strength of welded specimens tested perpendicular to weld line were almost equal to those of the base metal. But the yield strength and tensile strength of welded specimens tested parallel with weld line were a little higher than those of the base metal. The formability of laser welded TRIP steel was decreased compared with that of the base metal.
文摘Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.
基金supported by the National Natural Science Foundation of China (Grants 11002150,11332011,and 11402277)the Basic Research Equipment Project of the Chinese Academy of Sciences (YZ200930) for financia support
文摘Laser shock peening（LSP） is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP process.A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer.Assuming a linearly gradient distribution of impact toughness,the parameters controlling the impact toughness of the gradient hardened layer were given.The influence of laser power densities and the number of laser shots on the impact toughness were investigated.The impact toughness of the laser peened layer improves compared with an untreated specimen,and the impact toughness increases with the laser power densities and decreases with the number of laser shots.Through the fracture morphology analysis by a scanning electron microscope,we established that the Cr5Mo1 V steel was fractured by the cleavage fracture mechanism combined with a few dimples.The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.
基金The author thanks the Die and Mold Technology Promotion Foundation and the Amada Foundation for Metal Work Technology for their financial support.
文摘The effects of YAG laser welding conditions on mechanical properties andpress formability (bendability, stretch-formability and deep drawability) of high-strengthtransformation-induced plasticity-aided dual-phase (TDP) steel were investigated. Tensile tests andpress forming tests have been conducted for laser butt welded joints between two pieces of the samesteel. The tensile property and press formability were affected by the welding speed of 100 to1100mm/min and the energy of 6 to 9J/pulse. Excellent press formability was obtained with the energyof 6J/pulse and the welding speed of 300mm/min. It was concluded that the excellent weldability ofthe TDP steel can be ascribed to the weld joint formation.
