Advanced Materials Research Vols. 291-294

Abstract: In this paper, laser cladding was deposited Co-9Al-7.5W superalloy on 304 austenite stainless steel plate and cladding layer shape, dilution, Vickers hardness, microstructure and distribution of alloying elements were investigated. It was found that laser cladding layer has the characteristics of large dilution rate, fine microstructure, narrow heat-affected zone (HAZ), narrow alloy elements segregation, high Vickers hardness, high contents of alloying elements and low contents of Fe in the cladding layers.

Abstract: The joining materials of density ceramics and the fibre would be potential application value as seal materials at high temperature condition or in aerospace field. According to chemical composition consistent principle of ceramics/interfaces/fibre, the interlayer of mullite ingredient was designed which based on the ZTM ceramics composition. Using the absorber-microwaves properties of Al-Si alloy, the joining of ZTM ceramics and fibre materials with interlayer was achieved by microwave hybrid heating method. The experiment results indicated that the volume expansion of interlayer was about 4.8% when the content of Al-Si was 24 wt % in the compositions. The interlayer ingredients were mullite, zirconia and alumina after sintering. The fibres were better joint with interlayer by microwave sintering than by traditional method.

Abstract: In this investigation, in order to research the influence of magnetic field frequency on microstructure and properties of magnesium alloy welded joint, the AZ31 magnesium alloy plates which was 5mm were welded by GTAW under longitudinal magnetic field. The tensile test, hardness test and SEM were taken place to analyze the properties and microstructure of welded joint under different magentic field frequency. The acting mechanism of magentic field on welded joint was studied. The results show that: External magnetic field can improve the properties of magnesium alloy welded joint. The optimal mechanical property will be obtained when Im=2, f=20Hz, which the ultimate tensile strength is 231Mpa and the micro-hardness is 76.2HV.The magnetic field can produce electromagnetic stirring, which can refine crystal grain through breaking the pine-tree crystals with proper magnetic field current and frequency. The properties of welded joint will been improved by these fine crystal grain.

Abstract: Through adding enough calcium to C-Mn steel, the second phase particles of CaO can be found in C-Mn steel. The microstructure, the grain size and the toughness of CGHAZ in micro-calcium steel and no micro-calcium steel were studied by TEM, SEM and series impact experiment. The research shows that: the second phase particles CaO in micro-calcium steel have strong pinning force to grain boundary of CGHAZ; the second phase particles can retard grain growth in the course of welding in micro-calcium steel, fining grain at CGHAZ and improving the toughness of CGHAZ in micro-calcium steel.

Abstract: The maximum punch pressure force (TMPPF) of cold welding pressure affects not only the performance of the welding bonding but also the amount of the area of welding bonding. If punch force is more bigger, it may be take place cracks, stress concentration and welding concave pits, which affect application of materials and increase incidence of faults. The process that punch pressure of cold welding pressure applied on sheet materials to attain welding bonding is simplified beam in cold pressure welding. Under normal circumstances it is an important method to TMPPF by the manner of experiment, but the method to attain TMPPF is limited. In the paper completely inelastic collision theory is applied to explain the process of cold welding pressure, the theory of completely inelastic collision offers principle theory to attain TMPPF. In this paper, two supposes are put forward, on the basis of two supposes the critical velocity is attained. At the same time, critical kinetic momentum or critical kinetic energy will be attained. On the basis of the law of conservation of energy, energy balance equation is attained, which will drop in calculating difficulty of the non-linear process of cold pressure welding and decrease calculated amount. In this paper on the basis of the process of collision all phases are analyzed. Indeed elastic-plastic deformation phase is completely inelastic collision phase, and from point of view of collision to calculate energy loss. At the same time, to suppose other plate is utter stiff can attain critical velocity, thus, to achieve the equation of TMPPF.

Abstract: Welding residual stresses have an effect on many aspects of the integrity of structures but are normally one of the largest unknown stresses. Residual stresses are difficult to measure and to estimate theoretically but are often significant when compared with the service stresses. In this paper, measurement of residual stresses by X-ray diffraction technique using two different fitting methods (Gaussian and PearsonⅦ) was compared with analysis of a sample geometry by theoretical finite-element methods. The square map RS characterization of A7N01-T5 welds was shown. The results indicate RS measured by XRD and simulated by finite-element method show good qualitative agreement.

Abstract: In the present work, a specific oxide flux was used to systematically investigate the effects of activated tungsten inert gas (TIG) welding on the surface appearance, weld morphology, angular distortion, residual stress, and ferrite structure in type 316L stainless steel plates. MoO₃ flux used was packed in powdered form. The results showed that MoO₃ flux assisted TIG welding technique can produce a significant improvement in power density of heat source and weld aspect ratio, resulting in low angular distortion and residual stress levels. The MoO₃ flux assisted TIG welding associated with a rapid cooling rate of the welds, therefore exhibiting higher ferrite content in austenitic stainless steel 316L weld metals during the solidification after welding.

Abstract: The aim of this study was to investigate the effect of pulsed current welding parameters on angular distortion and residual stress of TIG weldment. Autogenous TIG welding was applied on type 316L stainless steel sheet to produce bead-on-plate welds. Angular distortion was determined using the mean vertical displacement method. Residual stress was determined using the hole-drilling strain- gage method. The results showed that the pulsed current TIG welding has a number of advantages, including lower heat input and consequently a reduction in distortion and residual stress of weldment.

Abstract: The ultrasonically brazing of 55 vol.% SiC_p/A356 composites in air has been investigated. When the ultrasonic vibration is applied for 0.5s, the oxide layer is still continuous at most places between the filler metal and the composites. The shear strength is only ~30% of that of the base composites. As the ultrasonic action time increases, the oxide film sufficiently disappears in the bond region, and the wetted area between the filler metal and SiC particles increases gradually. As a consequence of this, the shear strength of bonds also increases with the ultrasonically acting time. The maximum value of the shear strength of the bonds reaches 165.5MPa when the ultrasonic acting time increases to 5s, which is similar to the shear strength of the base composites.

Abstract: The effect of copper strips as an insert material on electrode failure has been studied during spot welding of galvanized sheets. The results showed that an extended electrode lifetime was obtained due to the use of copper strips between electrode and workpiece which prevented electrode from alloying with molten zinc and lowered the temperature of electrode tip. In addition, the presence of inserted copper strip increased the resistance of welding system, thus generated much more heat to form larger nugget The electrode degradation mechanism was basically caused by deformation at electrode tip and wear.