Materials Science Forum Vols. 704-705

Abstract: Because the enamel coatings has excellent ageing resistance and anti-corrosion performance, the service life of pipeline with enamel coatings as protective layer can be increased remarkably comparing with the ones with organic coatings. But when the pipeline is welded, the high temperature of welding arc will do harm to the bonding strength of the enamel coating and the base metal because of the differences of thermo-physical properties between them. In order to study the failure mechanism of enamel coating in the heat affected zone, the stress changing process of enamel/steel was studied through numerical simulation and the interface of enamel/steel was studied by welding thermal simulation technology. The results show that the weakness parts of the welded joints are the imperfect normalized zone and overheated zone. In the imperfect normalized zone, the micro-cracks generate at the interface of enamel/steel because high stress occurred and some coatings fused incompletely because of short staying time at high temperature that induced micro-cracks in the enamel coating under high welding stress, so it was one of the dangerous zones of HAZ. Because high tensile stress formed during cooling that was dangerous to the brittle enamel coating, the bond layer of enamel/steel was damaged by high temperature of welding and the pores generated at the interface of enamel/steel, the coatings of overheated zone could be pulled off from the base metal easily that caused the steel exposed to the corrosion medium directly without the protection of enamel coating, so it was another dangerous zone of HAZ. Keywords: enamel coating; numerical simulation; welding thermal simulation; failure mechanism; HAZ

Abstract: The laser welding of particle reinforced SiCp/ZC71 magnesium matrix composite was carried out using a Nd:YAG laser welding experimental system. The mechanical properties of welded joint was studied by tensile test and the morphology of tensile fracture, microstructure as well ingredient of welded joint were observed by SEM. The results show that welding technology for composites is harsher. SiC particles distributed uniformly and the white magnesium intermetallic compound dots disappeared in the laser welded seam because the precipitation of the magnesium intermetallic compounds was prohibited owing to the rapid solidification and cooling of the laser-welded seam.. There is no evident heat affect zone in the weld seams；The mechanical properties of welded joint are worse than those of matrix metal. The weld zone is the weakest part in welded joint. The much lower tensile strength of the seam compared to the tensile strength of the ZC71/SiCp substrate attributed to the surface roughness of the seams and some solidification micron-sized pores (especially between SiC particles and magnesium alloy matrix)，The fracture morphology of welded joint indicated a brittle cleavage fracture.

Abstract: In this paper, numerical modeling of inertia friction welding (IFW) for Inconel718 was performed using ABAQUS/Explicit with a 3D finite-element (FE) model and the coupled thermo-mechanical analysis. A new thermal input model has been deduced according to the characteristics of IFW and law of conservation of energy. The evolution of temperature field as well as the deformation pattern of the inertia welded joint has been predicted. It is shown that the interface temperature firstly increases rapidly to about 1100 °C within 3 s and then increases slowly. The energy input rate at the interface during the IFW process is closely related to the rotational speed and friction torque of flywheels. The temperature distribution at the interface is very inhomogeneous especially at the initial stage and finally tends to become uniform with the increase of time. Consequently, the flash start to appear as the interface temperature becomes homogeneous relatively and the plastic flow of metal at the interface happens. The verifying trial was carried out and the predicted temperature was compared with the experimental data measured by means of thermocouples. The shape of flash in simulation result was contrasted with the true shape of specimen under the same welding conditions. It is noted that the simulation results agrees well with the experimental results.

Abstract: A typical car stamping is analyzed in terms of FEM and its press signature is evaluated in detail. Microstructural, crystallographic texture and surface roughness evolution are studied in conjuntion with press performance. Careful press signature calibration is discussed in order to point out relevant aspects. Deep drawing steels are analyzed in terms of their evolution in microstructure and texture and path-related to the FLD (Forming Limit Diagram). 3D-Surface roughness is tentatively evaluated and related to the steel stampability.

Abstract: The ultra narrow gap welding process is suitable to the thick plate, ultra-thick plate welding with the characteristic of highly effective, high quality, low cost, low energy consumption and so on, and is easy to realize the mechanization and the automation. In this paper, the numerical simulation and technical experiment are used to study the form, grow and distribution regulation of the welding temperature field, stress field in welding joint with UNG MAW. Using the calculation to the thickness of 32mm, an example to simulate the magnitude and distribution of the residual stress in welding joint is given. Research shows that it is an effective analysis method to heat process and mechanic behavior in the welding by using finite element method numerical simulation and few experiments. Keywords: UNG MAW, Welding residual stress, Finite element method, Numerical simulation

Abstract: A three-dimensional computer code which is employed for modelling of fluid flow and heat transfer during braze gap filling on vacuum brazing has been developed by using SIMPLE algorithm and VOF method. By the aid of this program, the flow behavior of liquid filler metal, the location and wave of the free surface, as well as the temperature distribution can be simulated. In order to verify the computational results, experiments of vacuum brazing thin plate weldment with 0.03mm and 0.2mm braze gap have been made respectively. The result of comparisons between calculated data and experimental data show that the brazing gap is one of the most important technological parameters that influences the flow pattern of liquid filler metal during braze gap filling and the brazing seam formation process significantly, and the 3-D modelling of braze gap filling are rather accurate and reliable, thereby providing a useful and effective analytic tool for brazing technological design. Keywords: vacuum brazing; brazing gap filling; numerical modelling;

Abstract: The internal thermal transient stress and strain is difficult to be real time measured by experimental methods during welding, but the stress and strain is vital to understand the mechanism of the control on the wave-like deformation. Large nonlinear finite element software of MSC.Mrac is used to illustrate decrease of the wave-like deformation of the Ti-6Al-4V thin plate weldment by a new technique called welding with impacting rotation. Some simulation results such as temperature field, thermal transient stress evolution, elastic strain, plastic strain and distortion of thin plate are shown. By the help of the finite element analysis, the mechanism of control on the wave-like deformation was put forward, i.e. the residual stress was decreased by the certain amount plastic extensive deformation generated by the impacting revolution. Keywords: finite element analysis (FEA), Ti-6Al-4V, thin plate weldment, wave-like deformation, residual stress

Abstract: Based on ultrasonic frequency pulse tungsten inert-gas (TIG) welding for 0Cr18Ni9Ti austenitic stainless steel, the influence of pulse level parameters was investigated on the field of arc characteristic and arc force. The experimental results show that the pulse level parameters could have huge impact to arc characteristic and arc force. With the increased frequency of pulse level, arc plasma has a more obvious pinch effect, which causes the enhance of arc voltage. Similarly, the arc force can be improved obviously compared with that during conventional direct current (DC) TIG welding. By contrast, the sensitivity of welding characteristic to pulse current level frequency would reduce while the duty of pulse peak current increased.

Abstract: TiC particle reinforced Fe-based composite clad layer were in situ synthesized on surface of Q235 steel by Submerged arc Welding of the mixed powder of ferrotitanium, iron, chromium, nickel and colloidal graphite, etc. Microstructure of the clad layer were observed by scanning electron microscope （SEM） and Energy Disperse Spectroscopy (EDS). Wear resistance of the clad layer was tested on wear tester at room temperature compared with the base material Q235 steel. Microhardness of the clad layer was measured by microhardness tester. Results indicated that the fine TiC particles were formed by Submerged-arc Welding process, and the the TiC particles were dispersed in the matrix. The size of TiC particles was less than 2 μm. The microstructure of cladding layer consisted of TiC particles, martensite and austenite. The average microhardness of clad layer was HV_0.2601, which was about 3 times as high as the based metal Q235. On the conditions of same wear and room temperature, the weight loss of the base material Q235 is 10-15 times as much as the composite clad layer. The weight loss increase of the clad layer has a little change with the increase of load and the change of load is not sensitive to the weight loss of the clad layer. The clad layer has good load characteristics.

Abstract: The control arms, as an important part of automobile chassises, are using Aluminum alloy in more and more cases instead of steel. The ball joint sealing of control arms is a key process to chassises assembly and the sealing quality directly determine the lifespan of steering systems of automobiles. In this paper, based on the aluminum control arms, revolving-reveting processes for ball joint sealing of control arms are studied through finite element methods and experiments, and the effects of housing shape on the quality of ball joint sealing are also studied. The results show that the sealing quality for ball joint is related to the housing shape, and a better sealing quality can be achieved when the housing has a sloped edge, and verified by the experiments, which will provide elementary technical support to the ball joint sealing of automobile control arms. Keywords: Ball joint sealing; Revolving-reveting technology; Aluminium control arm.