Materials Science Forum Vol. 953

Abstract: Recently, the weight reduction of automotive body and crash safety become much more important factors. In addition, the corrosion resistance must be ensured for any material used in a structural part of automotive components. In an effort to satisfy these requirements, zinc-coated high strength steels have been developed. However, challenges to resistance spot weldability of zinc-coated high strength steel such as liquid metal embrittlement (LME) have emerged. In this study, the high temperature tensile test was conducted for 980MPa DP steel. And resistance spot welding was conducted for 980MPa DP steel and CP steel. The results show that the fracture behavior during tensile test are influenced by the temperature and strain rate. Cracks were formed on the weld surface of the DP steel after welding.

Abstract: Friction stir welded lap joints of 5083 aluminum alloy plates with thickness of 2mm and T2 pure copper plates with thickness of 3mm were prepared, and the microstructures and properties of lap joints were investigated. The results showed that Al and Cu interdiffusion occurred at the interface of the lap joints, the grains in the stir zone of Al were refined and the microhardness increased sharply. The joint of Cu can be divided into four parts, including the nugget zone (NZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM). Using the optimum welding parameters (rotation speed of 900rpm and welding speed of 100mm/min), the lap joints were well formed. There were fewer welding defects and the average shear tensile force reached 3.155KN. Also, the ductile-brittle hybrid fracture occurred at the transitional zone of the advancing side of the Al plates. XRD results showed that intermetallic compounds (IMCS) mainly composed of Al₂Cu and AlCu₄ were produced in the interface of the lap joints during welding.

Abstract: The purpose of this paper is to study the ballistic perforation resistance of double-layered steel plates subjected to impact by conical projectiles with different nose angles. Based on nonlinear finite element theory, different rigid projectiles vertically penetrating into double-layered Weldox 460E steel plates are simulated with LS-DYNA code. The configurations in the penetration process and failure modes of steel plates are given. The results of monolithic and layered targets are studied and compared for projectiles with different nose angles. It is revealed that compared to the monolithic plate, the double layer configuration is able to improve the ballistic limit for the target under impact by blunt-nose projectiles, and for sharp-nose projectiles the double layer configuration obviously weakens the ballistic resistance.

Abstract: A kind of gas nitriding method catalyzed by rare earth for 40CrNiMoA alloy steel was researched in this article. Effect of temperature on surface hardness of gas nitriding method catalyzed by rare earth, change law of layer depth with time at 500 °C were carried out and compared with normal gas nitriding. Based on these researches, gas nitriding method catalyzed by rare earth was optimized. The results show that gas nitriding catalyzed by rare earth can not only increase the nitriding speed, but also enhance the surface hardness of the nitriding layer. Using three - stage gas nitriding method catalyzed by rare earth and after 40 hours, the samples can meet the need of nitrided layer depth no less than 0.5mm, surface vickers hardness no less than 600.

Abstract: The Cu–3%Ag alloy was prepared by continuous unidirectional solidification technique. The composition distribution of continuous unidirectional solidification Cu–3%Ag alloy was analyzed. The effect of different mold temperatures on the composition distribution of alloy was studied. The results show that when the mold temperature is low, continuous unidirectional solidification Cu–3%Ag alloy has surface segregation. The morphology of segregation phase mainly presents stripe and water drop shape. When the mold temperature is high, the surface segregation begins to decrease and eventually disappear.

Abstract: ANSYS was used to establish the calculation model of the temperature field for 9% Cr heat-resistant steel pipes in local post-weld heat treatment (PWHT). And the computation model has been validated experimentally. Based on the numerical model, the temperature field distribution was simulated for different pipe lengths in local PWHT, and effects of pipe length on the temperature distribution of heat treatment was further studied. Results show that increase of pipe length has little influence on equivalent temperature measurement point, soak band (SB) width of outer wall and axial temperature gradient, while it causes temperature difference between outer and inner wall to increase and soak band width to reduce significantly in inner wall. And when pipe length increases to a certain extent, the temperature field tends to be stable gradually.

Abstract: This paper presents corrosion failure analysis of an underground natural gas pipeline. The pipeline material grade is 20# steel. The pipeline transfers multiphase fluid (Crude oil and water) from an oil well to an oil gathering plant. A portion of the line failed due to pitting corrosion under unknown circumstances. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are employed to characterize the scales and/or corrosion products near the failed portion. Based on visual and microscopic analyses and reviewing the background information, the following pitting corrosion sequences were identified: When the water ratio was smaller than 50%, the oil slick could cover the surface of the 20# test samples. Some uncovered surface would be corroded. When the water ratio was more than 70%, the surface of 20# steel contacted with more water. The average corrosion rate increased, and the corrosion products also formed, which would behave as a good diffusion barrier to prevent the underlying steel from further dissolution. Meanwhile, because of the corrosion products, the penetration rate also increased, the trend of local corrosion became weak with the water ratio continued to increase. The pitting corrosion varied with the water ratio because of the protection conferred by the oil slick or the corrosion product layer. Under such conditions, pits emerged on the steel surface until one of them grew faster and failed the oil pipeline.

Abstract: The effects of the montmorillonite clay surface modified with 0.5-5 wt% aminopropyltriethoxysilane and 15-35% octadecylamine (Clay-APTSO) on morphology, mechanical and thermal properties of poly(lactic acid) (PLA)/ethylene-octene copolymer (EOC)/Clay-APTSO composites were investigated. The blends of PLA/EOC with and without Clay-APTSO were prepared by melt mixing in an internal mixer. Scanning electron microscopy analysis observed the morphology of PLA/EOC blends demonstrated a phase separation of minor phase and matrix phase. The addition of Clay-APTSO in PLA/EOC blends showed significant decreased in droplet size of dispersed EOC phase, thus, Clay-APTSO acted as an effective compatibilizer in the PLA/EOC blends. The results of tensile properties found the decrease of Young’s modulus of PLA when added EOC due to the low modulus and flexibility of EOC. While the incorporation of Clay-APTSO increased significantly Young’s modulus of PLA/EOC blends at low EOC and Clay-APTSO content. The strain at break of the blends increased with the increase of EOC loading, this indicated the presence of EOC enhanced the elongation at break of PLA, while the addition Clay-APTSO reduced the strain at break of PLA/EOC blends. The tensile strength of all blend compositions improved when added Clay-APTSO and the tensile strength showed the highest value at 3 phr of Clay-APTSO. The thermal stability of PLA/EOC blends did not change when compared with neat PLA, and when added Clay-APTSO in the blends could improve the thermal stability of the PLA/EOC blends.

Abstract: Excellent mechanical behavior and low density of composite materials make them candidates to replace metals for many underwater applications. This paper presents a comprehensive study about the multi-objective optimization of composite pressure hull subjected to hydrostatic pressure to minimize the weight of the pressure hull and maximize the buckling load capacity according to the design requirements. Two models were constructed, one model constructed from Carbon/Epoxy composite (USN-150), the other model is metallic pressure hull constructed from HY100. The analysis and the optimization process were completely performed using ANSYS Parametric Design Language (APDL). Tsai-Wu failure criterion was incorporated in the optimization process. The results obtained emphasize that, the submarine constructed from Carbon/Epoxy composite (USN-150) is better than the submarine constructed from HY100. Finally, an optimized model with an optimum pattern of fiber orientations was presented. Hopefully, the results may provide a valuable insight for the future of designing composite underwater vehicles.