Advanced Materials Research Vols. 189-193

Abstract: The 316 stainless steel-alumina joining was prepared by a modified moly-manganese (Mo-Mn) process and a Ni net-embedded brazing method. The modified Mo-Mn process had a reaction layer between the Mo-Mn layer and the alumina substrate, followed by brazing with steel. The reaction products of the reaction layer with substrate and the Mo-Mn layer were investigated. The brazing method had a braze foil/compressed Ni net/braze foil set sandwiched between steel and alumina. The reactions among the Ni net, braze alloys and substrates were studied.

Abstract: The medium and heavy plate of 800 MPa grade ultra-fine grained steel was welded by CO₂ gas shielded welding using large line energy. The effect of cooling condition on microstructure and mechanical properties of welded joints was investigated. The results showed that the cases about significant grain size increasing and strength decreasing do exist in the heat affected zone of large line energy welded joints of 800 MPa grade ultra-fine grained steel. Grain growth and softening in the heat affected zone could be suppressed effectively by water cooling in the course of welding. The mechanical properties of welded joints could be significantly increased by water cooling, and the process of CO₂ gas shielded welding under water cooling is practical for joining ultra-fine grained steel using large line energy.

Abstract: During the welding of the wall plate of cylindrical structure, the edges of cylinder generates obvious wave-like deformation and affects subsequent assembly. In this paper, based on the numerical simulation method, welding deformation controlling by pre-stress method is studied. The effects of the pre-stress level and the welding sequence on the final deformation are discussed. The results show that the level of pre-stress can obviously control the welding deformation of the longitudinal beams, but can not control the welding deformation of transverse beams. Using the selected welding sequence: welding transverse beams firstly, exerting pre-stress, and then welding longitudinal beams, this welding sequence can reduce the wave-like deformation after welding.

Abstract: The metal magnetic memory (MMM) technology, a new nondestructive testing (NDT), has potentials of quantitative evaluation on welded joint defects. This paper investigates MMM signal quantitative characteristic of welded joint defects. Steel Q235 welded joint specimens, prefabricated with nonpenetration and slag inclusion, have been scanned by MMM testing instrument at 0kN, 150kN and 230kN tension loads on tensile machinery. For the nonpenetration specimens, MMM peak amplitude ΔHp and the peak width D adds with the increasing of tensile load, but gradient K varies a little. As for the slag inclusion specimens, the ΔHp and K enhances along with tensile load increasing, but the D varies a little. The X-ray testing results at 0kN, 150kN and 230kN tension loads show the validity of MMM signal characteristic. This means the feasibility of the weld qualitative and quantitative evaluation based on MMM method.

Abstract: Due to bad welds including small button, weld expulsion, and weld whisker etc., it is studied that the effect of constant and variable electrode force with servo gun on the weld quality of high strength steels with different thickness and materials. The results show that the electrode force plays an important role in resistance spot welding of AHSS as well as that of mild steels. Under the same welding current and time, better welds with higher tensile shear strength and larger nugget size can be obtained by optimizing electrode force curve using servo gun. The solutions could supply reference to study the prospect of servo gun in the joining of high strength steels.

Abstract: Lots of dynamic information, which can directly or indirectly reflect the quality of welded spot, is included within the electrode displacement signal of resistance spot welding process. In this research, the displacement signal is monitored and mapped into a 15×25 element bipolarized matrix by means of some method of fuzzy theory. Some welded spots are classified into five classes according to the prototype pattern matrixes. An effective RSW quality estimation system is developed based on Hopfield network when taking the tensile shear strength of the welded spot joint as the estimation index of welded spot quality. The results of cross-validation test shows that the Hopfield network can satisfactorily accomplish the task of classification of the welded spot and has board application prospects.

Abstract: For continuous casting roller with the poor Corrosion resistance, developed the PLJ225 flux-cored wire welding with nitrogen for continuous caster roller, flux of 107 matches, and used a suitable welding process for surfacing continuous caster roller. Continuous caster roll after surfacing not only has good resistance to abrasion, heat-fatigue resistance has a good performance, life expectancy increased by 1 ~ 6 times more.

Abstract: Focusing on the need of actual production, physical analogue experiments were done on the 400MPa ultra fine grained steel under different welding heat circulations. The experiment results showed that grains growing up and performance dropping was inevitable, the coarsening temperature range was 1000~1200 ; where the heating temperature was 800 in the Heat Affected Zone, the soften was the most obvious, but when the cooling rate t_8/5<10s, the soften disappeared; speeding up the cooling rate could improve the microstructure of the Heat-affected Zone effectively and made the mechanical properties of the joint better than that of the base metal.

Abstract: The effect of chemical species of copper alloys on growth of intermetallic compounds (IMCs) at interface of solder/copper alloys for lead frame was investigated. The results have revealed that Cu is the main diffusing species during aging. After aged at 160°C for 300h, only a Cu₆Sn₅ IMC layer is observed at SnPb/copper alloys interfaces. The growth rate of IMC on the Cu-Cr-Zr system alloys and Cu-Ni-Si alloys was much slower than that of IMC on the C19400 alloy. The Pb phase and voids were found to be inside the Cu₆Sn₅ phase. Chromium, one of the alloying element in Cu-Cr-Zr-Zn alloys, has found to be segregated at the interface between the copper alloy/Cu₆Sn₅. Zn and Zr in the Cu-Cr-Zr-Zn system alloy are enriched in small amout inside the IMC. These observed results were discussed and analysed on the baisis of diffusion and growth kinetics.

Abstract: The beam is assumed to obey a three-dimensional viscoelastic fractional derivative constitutive relations, the mathematical model and governing equations of the quasi-static and dynamical behavior of a viscoelastic Euler-Bernoulli beam are established, the quasi-static mechanical behavior of Euler-Bernoulli beam described by fractional derivative model is investigated, and the analytical solution is obtained by considering the properties of the Laplace transform of Mittag-Leffler function and the properties of fractional derivative. The result indicate that the quasi-static mechanical behavior of Euler-Bernoulli beam described by fractional derivative viscoelastic model can reduced to the cases of classic viscoelastic and elastic, the order of fractional derivative has great effect on the quasi-static mechanical behavior of Euler-Bernoulli beam.