Advanced Materials Research Vols. 881-883

Abstract: Al-Mg-Si alloy is used to investigate the bake-hardening response as automotive body panels. Natural aging followed by artificial aging at 170°C was carried on to study the effect of delaying at room temperature. Two methods are carried on to investigate the effect of pre-treatment on hardening response of Al-Mg-Si alloy. One is pre-aging in the range 80-140°Cfollowed by artificial aging at 170°C after natural aging for the same periods, and the other is retrogression treatment followed by artificial aging at 170°C after natural aging for the same periods. The properties of the alloy are tested by Vickers hardness measurements. And it is found that the optimal pre-ageing is 170°C for 30min and the opimal retrogression treatment is 230°C for 15s.

Abstract: The plates under the compound energy field and the general ones were prepared by introducing ultrasonic and electromagnetic field at the key part of the cast-rolling area, and then the final aluminum strips with thickness of 0.27 mm were prepared through cold rolling and annealing. The microstructures and properties were investigated by optical microscope (OM), static/dynamic universal testing machine and scanning electron microscope (SEM). The results show that by applying compound energy-field, grains are significantly refined and the mechanical properties are improved. Compared to the general cast-rolling strips, the ultimate tensile strength, yield strength and elongation of compound energy-field aluminum strips are improved by 32.93%, 38.91% and 6.25%, respectively.

Abstract: Preparation and the characteristics of environment-friendly Ce-Ti-Mn conversion coating on aluminum alloy 6061 were investigated by XRD, FESEM, EDS, TEM and AFM in this paper. It is indicated that coating characteristics such as the surface morphologies, microstructure and corrosion resistance, are greatly influenced by the formation technology at room temperature. The constituents and their concentration, and pH value of the conversion solution have an important role on the feature of Ce-Ti-Mn conversion film, which will significantly influence on the continuity, compactness and the crystalline structure of particles of the film. The concentrations of the main salt K₂TiF₆ and oxidizer KMnO₄ have significant effect on the characteristics of the conversion coating. The Ce-Ti-Mn film grows in a lamellar way, composing of oxide and/ or hydroxide phases of Ce, Ti and Mn, some of which are amorphous. The formation mechanism of the Ce-Ti-Mn conversion coating is discussed in detail.

Abstract: In this study, a combination of a two-step sintering and a particle size gradation technique was used to prepare cermet samples. We focused on the impact of the AlF₃ additive on the performance of the cermet. We found that the addition of AlF₃ doesnt significantly improve the density and porosity of Ag-NiFe₂O₄, since the addition of the AlF₃ did not reduce the particle size, nor did it promote the tight packing of NiFe₂O₄ in a spinel-based cermet. However, we did observe a significant enhancement in its conductivity. The sample with 3% additive has the highest conductivity at 22.53S·cm^-1 at 900°C, nearly 3.8 times better than the pure sample. An Analysis of the cermet microstructure showed that adding AlF₃ can improve wetting between the ceramic phase and the silver metallic phase. It also facilitates the distribution of silver along the contour of the ceramic particles, which contributes to the improved conductivity of the nickel-based cermet.

Abstract: The microstructure and mechanical properties of magnesium alloy AZ61wtih1% Sn addition has been studied in this paper. The results show that the addition of 1% Sn can refine the grain size and improve the microstructure morphology of β-Mg₁₇Al₁₂ phase. The addition of Sn can cause the formation of Mg₂Sn phase in AZ61 alloy, which can effectively enhance the mechanical properties of magnesium alloy AZ61 at room temperature and 150°C.

Abstract: Stellite190 cobalt alloy coating was deposited on 45 carbon steel by electro-spark deposition. Formation mechanism, microstructure, phase composition and mechanical properties of the coating were researched, fracture mechanism of the coating was analyzed. The results indicate that, the coating has dense and well distributed microstructure, mainly composed of Co, (CoCrW)₆C, Cr₇C₃. The coating presents excellent mechanical properties with a tensile strength of 731.83 MPa, a bonding strength of 213.01 MPa and good peeling resistance. The mechanism for tensile fracture of the coating is dimple fracture, and for shear fracture is cleavage fracture.

Abstract: Ni-based alloy submicron WS₂/CaF₂ composite coatings were successfully produced through high velocity oxy-fuel (HVOF) spraying process. Microstructure characterization and morphology analysis on coatings were conducted using scanning electron microscopy and X-ray diffractometry. Tribological properties of coatings were carried out using a pin-on-ring tribometer at room temperature and 500°C, respectively. Results showed that WS₂ in particles did not entirely decomposed during spraying process, submicron WS₂ and CaF₂ were uniformly distributed throughout the coating. Which lead a dense coating and a lower friction coefficient and better wear resistance. In ambient temperature, WS₂ in coatings played a main role of lubrication, friction coefficient of coatings was in the rage of 0.25~0.35. But with the increasing of temperature, WS₂ failed to provide solid lubricating films for pyrolysis, and CaF₂ did not fully transfer from brittleness to plasticity, restrained solid lubricating film forming, friction coefficient reached to 0.45. Furthermore, average adhesive strength between coating/substrate was above 30MPa, which had positive affect on wear resistance of coatings.

Abstract: Elastic-plastic J-integral and plastic limit load were described by finite element (FE) analysis for single hole-edge crack in plate under far field biaxial load. In this paper, the effect of biaxial load ratio (from -1 to 1) on elastic-plastic J-integral and plastic limit load was studied, the values of coefficient h1 for J-integral engineering estimation formulas were given and the effect of material hardening on plastic limit load was discussed. The result obtained from this work provides reference for fracture evaluation, so it can be used in engineering accurately and expediently.

Abstract: The butt welding test has been performed on QCr0.8 bronze by electron beam welding. Microstructure of the joint was examined by optical microscopy and scanning electron microscopy with EDS. Microhardness of the joint was determined to evaluate the mechanical property of the joint. The fusion zone and the heat affected zone became the weak area of the joint due to the growth of grains and the redissolve of strengthening phase. The decrease of strengthening phase has a major influence on the microhardness reduction of the joint..

Abstract: For the simulation of cold rolled 20Cr steel pipe rolling process the DEFORM-3D being used, the simulation results include the equivalent stress, equivalent strain and rolling force distribution in deformation zone. The stress state of the pipe reducer section is analyzed, analysis shows that the simulation result is approximate the theoretical calculation. The simulation result shows the roll pass and openning effect on the rolling pipe. A view put forward is to compare the simulation results with the actual production and find out their differences. A proposal is made to establish a corresponding database based on simulation and production data.