Advanced Materials Research Vols. 314-316

Abstract: Copper and copper alloy are more difficult to weld than steel in terms of many reasons. As a new technolsgy, copper and copper alloy’s manual self-propagating high-temperature synthesis (SHS) technology was introduced in this paper. Through research of weld and analysis of manual SHS welding process, mechanism of copper and copper alloy’s manual SHS welding is expounded. This type of weld was only researched in terms of some aspects, including welding method, weld technique parameter, weld operate technique. The chemical compositions of the weld rod was the key to the final weld quality. The powders include thermit, slagging elements and alloying addition. When the content of (CuO+Al) was 60%wt~80% in the thermit, the rod showed excellent combustion behavior and the test plates H62 were welded successfully. The slag system of CaO-Al2O3-SiO2 have the lower melting point and high deformation power, which fit to meet the need of the weld slag system of copper and copper alloy’s manual SHS welding. The high melting point Al2O3 can be digested and absorbed in two ways, generating CuO•Al2O3 ceramics and reducing the melting point to float upward into slag with the help of the solvent.

Abstract: In this paper, some deep cryogenic treatment experiments are first applied to 5A06 aluminum alloy welded joint at liquid nitrogen temperature （-155°C ）for 4h, 8h, 10h respectively. 5A06 alloy welded joints before and after deep cryogenic treatment are observed by X-ray diffraction and scanning electrical microscopy. The experimental results have shown that the deep cryogenic treatment causesβphase of alloy to disperse and makes the grain smaller than that of joint before deep cryogenic treatment. Therefore, the mechanical properties of 5A06 alloy welded joints after deep cryogenic treatment are greatly improved.

Abstract: Seam tracking is an important field to obtain good welding quality. During the high-power fiber laser welding, the laser beam focus must be controlled to track the welding seam accurately. A method of detecting the offset between the laser beam focus and the welding seam based on analyzing the keyhole features was researched during high-power fiber laser butt-joint welding of Type 304 austenitic stainless steel plates at a continuous wave fiber laser power of 10 kW. The joint gap width was less than 0.1mm. An infrared sensitive high speed camera was used to capture the thermal images of a molten pool in welding process. Two parameters called the keyhole centroid and keyhole shape were defined as the eigenvalues of seam tracking offset to determine the offset between the laser beam focus and the desired welding seam. The welding experiments confirmed that the offset between the laser beam focus and the welding seam could be monitored and estimated by the keyhole centroid and keyhole shape parameters effectively.

Abstract: The spatters created during laser welding are considered as essential information for welding quality inspection. This paper proposes a laser welding quality inspection method based on the high-speed visual detection. A high-power disk laser bead-on-plate welding of Type 304 austenitic stainless workpiece was experimented and two high-speed cameras were used to capture the spatter images. Spatter feature parameters were extracted by image processing, and the spatter volume was used to evaluate the welding quality. By comparing the spatter information with molten pool width, this paper investigates the internal relation between the welding quality and the spatter feature parameters. Experimental results proved that the proposed spatter feature extraction method help to guarantee an accurate evaluation on the quality of high-power disk laser welding.

Abstract: During deep penetration laser welding, a keyhole is formed in the molten pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. The configuration and characteristics of a keyhole are related to the welding stability. In a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser, an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. The configurations of a keyhole were analyzed through image processing techniques such as median filtering, wiener filtering and gray level threshold segmentation to obtain the edge of a keyhole. The width and the area of a keyhole were defined as the keyhole characteristic parameters, and the deviation between the laser beam and weld center as a parameter reflecting the welding stability. By analyzing the change of the keyhole characteristic parameters during welding process, it was found that these parameters were related to the welding stability. Welding experimental results and analysis of the keyhole characteristic parameters confirmed that the welding stability could be monitored and distinguished by a keyhole configuration during high-power fiber laser welding.

Abstract: High cycle fatigue behavior of MB8 magnesium alloy were investigated using an up-and-down load method. High cycle fatigue tests were carried out up to 107cycles at a stress ratio R=0.1 and frequency of 90Hz on specimens using a high frequency fatigue machine. Fatigue fracture surfaces of specimens that in the high cycle fatigue tests were also observed using a scanning electron microscope for revealing the micro-mechanisms of fatigue crack initiation and propagation. The results showed that fatigue limit of MB8 alloy at room temperature is 90.2 MPa under the numbers of cycle to failure Nf=107 conditions using up-and-down method calculation. The fatigue strength of the alloy is about 34% of its tensile strength. The micro-fatigue fracture surface of MB8 alloy included three representative regions. These regions are fatigue initiation area, fatigue crack propagation area and fatigue fracture area. Fatigue cracks of MB8 alloy initiate principally at surface and subsurface, and propagate along the grain boundary. The fatigue striations of fatigue crack propagation area are not clear. The fatigue fracture of test specimens show the rupture characteristics of dimple.

Abstract: The microstructure, the regular and mechanism of various parameters on formation of weld bead of Mg alloy AMCa403 using a laser welding were investigated. The results show that sound welds without major defects can be produced. Two welding modes of deep penetration welding, heat conduction welding were found, and heat input was found to be the main factor for welding mode and shape. The microstructure of weld metal is significantly finer than the base metal. At the same power, with the increase of welding speed, the microstructure of weld metal is much finer.

Abstract: In this paper a bonding-FSSW hybrid method is proposed and the joining procedure as well as the microstructure and performance of bonding-FSSW hybrid joints of AZ31 aluminum alloy is examined . The results show that the bonding agent has little influence on the forming and mechanical property of FSSW nugget, the shear-resisting property of the hybrid joints with sealing glue is equivalent to FSSW joints, in bonding-FSSW hybrid joint with high-strength bonding agent, the shear-resisting property of joints are apparently superior to that of pure FSSW or bonding joints. Tiny and uniform equiaxial grains are formed in the WN(Welding nugget zone) and coarse grains are formed in TMAZ (Thermomechanically affected zone) and HAZ (Heat affected zone), but with unequal size. The good properties of the hybrid joints are obtained by choosing the optimal joining parameter.

Abstract: This paper is mainly a study the diffusion bonding of 3Y-TZP/SUS440 by using the chemical bonding method. In the bonding interface of 3Y-TZP and SUS440, the Ti-Cu (brass) powder/sheet was used as bonding materials. After bonding process, multi-alloy field with Fe-Ti and Fe-Cu have been confirmed by EPMA determination. Through the microstructure observed by AFM and SEM, bonding boundaries of 3Y-TZP/SUS440 by Ti-Cu powder/sheet had good formation. The distribution of the residual stress on near interface was measured by XRD method. By using of these results, the mechanism of the ceramic and stainless steel was discussed.

Abstract: In this paper experimental and FEA methods were used to study the damage propagation and failure properties of stiffened composite panels with discrete-source damage. The influence of discrete-source damage on residual strength of the composite panel was also investigated. The research results indicated that notched composite panel was suitable to simulate the damage property of stiffened composite panel with discrete-source damage. It has showed that there is high strain concentration at the notch end. And break-through of the stringer can make the load path changed. Based on different failure criteria, FEA method with progressive failure procedure was used to simulate the damage progression and failure procedure of the notched stiffened composite panel effectively. The analytical result was in good correspondence with the experimental data.