Research on cold crack sensitivity of high-strength wear-resistant steel NM360 after welding

Due to the high amount of carbon and diffusible hydrogen, high-strength wear-resistant steel NM360, which is widely used on excavating machinery, always tends to develop cold crack after welding. Heat affected zone (HAZ) is the weakest part in a welding joint and is the most probable location for the generation of welding cold crack. In this paper, the effects of preheating temperature and heat input on welding cold crack sensitivity of NM360 steel have been studied by using implant tests. It is found that the preheating temperature and interlayer temperature during CO2 arc welding of NM360 steel should be 100 °C or 125 °C to prevent the occurrence of welding cold crack. The critical rupture stress and rupture time under high stress can be improved significantly with a high enough preheating temperature. However, heat input increase has little effect on critical rupture stress. Fracture analysis after performing implant test s indicates that the fracture in HAZ is typical hydrogen-induced cracking under high stress (≥ σcr). In addition, NM360 steel in HAZ has an intercrystalline quasi-cleavage fracture mode. The area ratio of brittle fracture is increased by increasing test stress

Numerical simulation of material flow in AA6082 during friction stir spot welding

Friction stir spot welding (FSSW) is a new solid state joining technology based on the linear friction stir welding which can be used to replace the conventional resistance spot welding as well as riveting. However, some key problems such as heat transfer and thermoplastic material flow have not yet been studied sufficiently and block the application of this advanced technology. This paper presents the coupled thermo-mechanical viscoplastic finite element formulation based on the character of FSSW. The model was calibrated by comparing temperature history between simulation results and experimental data and subsequently used to investigate the effective strain rate and material flow in joint. The temperature study showed that the simulation and experiment results coincided well with each other thus proofing the correctness of the model. The simulation results showed that the effective strain rate distribution were not uniform. The material close to the pin’s cylindrical surface had a higher effective strain rate than that of the other material. The materials in weld centre mainly experienced a compression process and the other material under the tool experienced both compression and shear process

Effect of different surface pretreatment method on vacuum brazing joint properties of AlSi50 alloy

In this paper, the effect of different surface pretreatment method on properties of vacuum brazed joint of AlSi50 alloy was investigated. The surface pretreatment methods of specimen before brazing include sanding, NaOH corrosion, HCl corrosion, H2SO4 corrosion and nickel plating. The experimental results indicate that the width of brazing joint varies with different surface pretreatment methods. The joint with sanding pretreatment, has the largest brazing seam width of 20 μm. Meanwhile, joint with H2SO4 corrosion has the narrowest brazing seam width. The brazing filler metal can wet and spread on different pretreated specimen very well. Spectrum analysis indicates that nickel-plate on AlSi50 surface, can interact with brazing filler metal, which increases mechanical property of brazing joint. For brazing of AlSi50 alloy, the optimal pretreatment method is nickel plating. After nickel plating pretreatment, brazing joint has the maximum shear strength 82.05 MPa by using brazing filler metal Al52-Cu33-Mg12-Ni3 and following technological parameters: brazing temperature 580 ℃, soaking time 30 min and pressure 3 MPa

Vacuum brazing between SiCp/6063 Al MMCs and Fe-Ni alloys

This research paper deals with the joining of different materials such as SiCp/6063Al MMCs and Fe-Ni alloys by means of vacuum brazing with active filler metal Ag47-Cu18-In17-Sn17-Ti1. With the optimal process parameters, i.e., brazing temperature 580 °C, soaking time of 30 min and vacuum degree of 6.5×10-3 Pa, the joint shear strength can achieve the maximum of 56 MPa. Once the brazing temperature of 580 °C has exceeded the solidus temperature of SiCp/6063Al MMCs, the specimen can still keep the original shape due to the stiffness of composites. Sufficient diffusion between brazing filler metal and SiCp/6063Al MMCs could occur across the interface in liquid phase considerably faster than that in solid phase. The component analysis indicates that the elements in filler metal such as Ag, Sn and In can diffuse into SiCp/6063Al MMCs, which is believed to be beneficial for the joint quality

Study on SiCp/6063Al composites laser welding process with Al75Cu20Ti5 foil interlayer

This experiment chooses 6063 aluminum matrix composites containing 55~75% SiC particle reinforcing phase as the parent metal and Al75Cu20Ti5 foil as the interlayer. The laser power, defocusing amounts and welding speed are discussed using three important parameters for the joint forming, microstructure and shear strength. The result shows that the weld width is mainly affected by laser power, and the weld penetration is almost determined by the defocusing amount. The welding speed has a certain influence on both weld width and weld penetration. When suitable laser heat input is adopted, superior weld appearance and satisfied shear strength could be obtained. The highest shear strength is 217MPa, with the laser power of 520W, the defocusing amounts of -1mm, and the welding speed of 1.5cm/s

Finite element analysis of welding residual stress of aluminum plates under different butt joint parameters

A thermal-elastoplastici finite element method was built to simulate the process of variable polarity plasma arc welding (VPPAW) for aluminum alloy plates. The welding temperature and stress fields of the aluminum plates with different butt joint parameters(intervals of the joints: D=0.3 mm, 2 mm; and unfitness of the joints: L= 0.3 mm, 2 mm) were calculated using a 3D double-ellipsoidal heat source model. The residual stresses of the welded plates were predicted; the results showed that the unfitness of the joint has a greater impact on the welding residual stresses than that of the interval. The simulated and experimental results were compared and they are consistent well with each other