Investigation on the deposition rate and the dilution ratio of plasma surface welding

A new kind of plasma technology with both high deposition rate and low dilution ratio was developed under the calculation and analysis of the arc flame characteristics of plasma arc,the kinematics behavior of powder and powder's heating in the arc. Compared with normal plasma surfacing method, the idea using constricting nozzle with small orifice diameter, long plasma arc and increasing the distance from meeting point of the two beams of powder to workpiece, to achieve the goals of high deposition rate and low dilution ratio, was put forward here. In order to prove this idea, a set of experimental system was built up and obtained satisfied results including high deposition rate(more than 25 kg/h )and low dilution ratio(less than 5%). The success of this study offers a promising prospect for developing the powder plasma surface welding in China and may open a way to improve this technology further in efficiency and quality.

Solidification crack susceptibility of aluminum alloy weld metals

The susceptibilities of the three aluminum alloys to solidification crack were studied with trans-varestraint tests and tensile tests at elevated temperature. Their metallurgical characteristics, morphologies of the fractured surface and dynamic cracking behaviors at elevated temperature were analyzed with a series of micro-analysis methods. The results show that dynamic cracking models can be classified into three types. The first model has the healing effect which is called type A. The second is the one with deformation and breaking down of metal bridge, called type B. The last one is with the separation of liquid film along grain boundary, called type C. Moreover, the strain rate has different effects on crack susceptibility of aluminum alloys with different cracking models. ZL101 and 5083 alloys belong to type A and type C cracking model respectively, in which strain rate has greater effect on eutectic healing and plastic deformation of metal bridge. 6082 alloy is type B cracking model in which the strain rate has little effect on the deformation ability of the liquid film.

FEM SIMULATION FOR LASER FORMING PROCESSING

Laser forming involves heating sheet metal workpiece along a certain path with adefocused laser beam directed irradiate to the surface. During laser forming, a tran-sient temperature fields is caused by the irradiation and travelling of a laser beam.Consequently, thermal expansion and contraction take place, and allows the thermal-mechanical forming of complex shapes. This is a new manufacturing technique thatforming metal sheet only by thermal stress. Therefore, the analysis of temperaturefields and stress fields are very useful for studying the forming mechanism and con-trolling the accuracy of laser forming. The non--liner finite element solver, MARC, isemployed to solve the thermal--mechanical analysis. Using this model, the stress andstrain distribution of pure aluminum plate with different thickness are analyzed. Theinfluence of scanning speed on temperature fields and plastic strain of metal sheet un-der the condition of constant line energy are also presented. Numerical results agreewell with the experimental results.

Performance of GH4169 brazed joint using a new designed nickel-based filler metal via cluster-plus-glue-atom model

A novel Ni-Cr-Si-B filler metal with the cluster formula of[Cr-Ni12]B2Cr+[B-Ni8Cr]BSi Cr based on the cluster-plus-glue-atom model was designed for vacuum brazing GH4169 alloy.The effect of brazing temperature and brazing time on microstructure and shear strength of GH4169 alloy joints was investigated.The brazed seam was mainly composed ofγ-Ni solid solution.(Nb,Ti)-rich phase and(Cr,Nb,Mo)-rich borides distributed in diffusion zones.The diffusion and aggregation of B,Cr,Nb,and Mo resulted in the variation of phase contrast and morphology of borides.Coarse precipitations in the joint brazed at1240℃consisted of borides,Laves phase andδphase.The shear strength of joints was principally dominated by the brittle precipitations in diffusion zone,and the homogenization of microstructure improved the room-temperature shear strength to 820 MPa with the high-temperature shear strength of 627 MPa for the joint brazed at 1240℃/20 min.The joint fractured in diffusion zone and brazed seam,and the existence of borides and Laves phase in diffusion zone provide the potential origin for crack growth.