Beam oscillating parameters on pore inhibition,recrystallization and grain boundary characteristics of laser-arc hybrid welded AZ31 magnesium alloy

Oscillating laser-arc hybrid welding of AZ31B magnesium alloy was carried out,the effects of beam oscillation parameters on pore inhibition,microstructure,grain boundary characteristics and tensile properties were investigated.The results showed that the pore formation can be inhibited with oscillating frequency higher than 75 Hz and radius smaller than 0.5 mm.The columnar grains neighboring the fusion line can be broken by the beam oscillation behavior,while the grain growth was promoted with the increase of frequency or radius.It should be noted that the coincidence site lattice(CSL)boundaries were mainlyΣ13b andΣ29 boundaries,which were contributed by{10■2}tensile twins and{11■2}compression twins,respectively.The total fraction of CSL boundaries reached maximum at radius of 0.25 mm and frequency of 75 Hz,which was also confirmed as the optimized parameters.In this case,the elongation rate increased up to 13.2%,12.8%higher than that of the weld without beam oscillation.Finally,the pore formation and inhibition mechanisms were illustrated according to the state of melt flow and keyhole formation,the abnormal growth was discussed basing on secondary recrystallization,and the relationship among the pore formation,grain size,boundary characteristics and weld toughness were finally established.

Microstructure homogeneity and mechanical properties of laser-arc hybrid welded AZ31B magnesium alloy

Laser-arc hybrid welding of AZ31B magnesium alloy was carried out,the effects of welding parameters on weld formation,microstructure homogeneity and mechanical properties were investigated.The results showed that laser-arc hybrid welding was beneficial to improve the weld formation of magnesium alloy by inhibiting the defect of undercut and pores.The weld microstructure was mainly columnar grains neighboring the fusion line and equiaxed grains at the weld center.It was interesting that the grain size at the upper arc zone was smaller than that at the lower laser zone,with the difference mainly affected by laser power rather than welding current and welding speed.The welding parameters were optimized as laser power of 3.5 kW,welding current of 100 A and welding speed of 1.5 m/min.In this case,the weld was free of undercut and pores,and the tensile strength and elongation rate reached 252 MPa and 11.2%,respectively.Finally,the microstructure homogeneity was illustrated according to the heat distribution,and the evolution law of tensile properties was discussed basing on the weld formation and microstructure characteristics.

Research on laser-arc hybrid welding technology for long-distance pipeline construction

In recent years, the research on pipeline laser-arc hybrid welding technology has been the important and difficult in the field of welding all over the world. China Petroleum Pipeline Research Institute Co. Ltd. has firstly developed pipeline laser-arc hybrid welding system in China, and executed the welding tests based on X70/X80 steel. Preliminary experiment results showed that hybrid welding could meet the requirements of related standards such as API1104,ASME,etc., the mechanical properties of girth seam are qualified in the case that there were no internal defects. With the development of high-power fiber laser and the continuous improvement of welding equipment, laser-arc hybrid welding technology for pipeline field welding will be available soon.

Microstructure and properties of laser-arc hybrid welding of high-strength low-alloy steel

Laser-arc hybrid welding has the characteristics of optimal surface formation and greater penetration;it is extensively used in the welding of plates of medium thickness.However, for hybrid welding of lasers, the welding seam cooling rate is rapid;thus, the welding seam has a higher tendency to significantly harden, which has a negative impact on the weld quality of the high-strength low-alloy(HSLA) steel plates of medium thickness.In this study, laser-arc hybrid welding is performed on the BG890 QL HSLA steel produced by Baoshan Iron & Steel Co.,Ltd.,and the quenching tendency of the welded structure is examined.The results demonstrate that the specific growth direction of the columnar crystal structure of the laser-arc hybrid welded joint is obvious.However, at the center and top of the welded seam, there are equiaxed crystals.The impact properties at room temperature and-40 ℃ of the weld area are 58.0 J and 40.0 J,respectively, and those of the heat-affected zone(HAZ) are 147.0 J and 66.5 J,respectively.The impact performance can meet these requirements.Laser-arc hybrid welding of HSLA steel can yield strong and durable welds and the HAZ structure to meet the requirements of engineering applications.

Numerical simulation of temperature field in laser-arc hybrid welding of wear-resistant steel

Using ABAQUS software and cylindrical ellipsoid and body heat sources with a peak-heat-flux- attenuation function, a finite element model of the temperature field in the laser-arc hybrid welding of 4.5-mm BW300TP wear-resistant steel is proposed. The proposed model considers convection, radiation, molten pool flow, and heat conduction effect on temperature. A comparison of the simulation and actual welding test results confirms the reliability of the model. This welding heat-process model can provide the cooling rate at any position in the heat affected zone （HAZ） and can be used as a reference for the analysis of material properties and for process optimization.

Application and development in railway vehicles trend of new welding technologies manufacturing industry

This paper introduces the application of new automatic welding technologies in railway vehicles manufacturing industry, and presents the state of art of advanced friction stir welding technology, semi-penetration laser welding technology and laser-arc hybrid welding technology in manufacturing aluminum alloy body shell, stainless steel body shell and bogie. This paper also analyzes the application and development trend of three welding technologies in the future.

FEM Simulation of Distortion and Residual Stress Generated by High Energy Beam Welding with Considering Phase Transformation

A series of experiments was carried out so as to elucidate the effect of the phase transformation in the cooling process on welding distortion and residual stress generated by laser beam welding (LBW) and laser-arc hybrid welding (HYBW) on the high strength steel (HT780). Then, the experiments were simulated by 3D thermal elasticplastic analysis with FEM (Finite Element Method) which was performed with using the idealized mechanical properties considering the transformation superplasticity. From the results, the effects of the phase transformation on welding distortion and residual stress generated by LBW and HYBW were elucidated. Furthermore, the generality of the idealization of the mechanical properties was verified.

电弧状态对铝合金激光-电弧复合焊接工艺过程稳定性的影响

焊接过程稳定性是决定焊缝质量的重要因素,而焊接飞溅和焊缝表面形貌是焊接过程稳定性的直接体现。为了得到稳定的铝合金激光-MIG电弧复合焊接过程,本研究采用高速摄影的方法统计焊接飞溅数量,并分析焊缝表面成形质量,对焊接过程稳定性进行了综合定性评价,结合激光焊接与电弧焊接基本原理,探讨了减少飞溅、稳定焊接过程的原理。在本试验条件下,提高纯Ar保护气的流量、电弧弧长和光丝间距,降低电弧电磁收缩力,可以减少飞溅数量。复合焊接飞溅数量减少的主要原因可以归结为两点:激光对熔池的预热作用扩大了熔池前端的面积,使熔滴融入熔池的过程更平稳;工艺优化使电弧对熔滴的作用力保持在合理范围。相关结果为复合焊接稳定的工业应用奠定了工艺基础,指明了工艺优化方向。

Microstructure and mechanical properties of weld metal in laser and gas metal arc hybrid welding of 440-MPa-grade high-strength steel

Fiber laser and gas metal arc hybrid welding of 440-MPa-grade high-strength marine steel was carried out at different welding speeds.The influence of welding speed on the micro structure and mechanical properties of weld metal was investigated.The weld-metal microstructure mainly consisted of pre-eutectoid ferrite,side-plate ferrite,acicular ferrite and lath bainite at a low welding speed.With the increase in welding speed,acicular ferrite and lath bainite were the dominant weld-metal microstructures.All samples failed at the base metal during tensile tests,which indicates that there is no soft zone in the hybrid welds.The welding speed had a significant effect on the impact toughness of the weld metal.The impact absorbed energy of the weld metal increased from 35 to 105 J with the increase in welding speed from 0.8 to 2.0 m/min.Large amounts of acicular ferrite and lath bainite were formed in the weld metal at a high welding speed,which resulted in an excellent impact toughness.