Advanced Materials Research Vols. 1120-1121

Abstract: In this paper, common continous annealing (CCA) and ultra-fast annealing (UFA) were carried out on a cold-rolled interstitial-free (IF) steel, respectively. The microstructure of the annealed IF steel was characterized by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The mechanical property was examined using tensile test. The optimum annealing process parameters were then obtained. The results showed that, the recrystallization occurs at the temperature in the range of 780-830°C. The fraction of equiaxed grain increases with the annealing temperature increasing. The well combination of mechanical properties and formability was obtained when the IF steel annealed at 820°C, which was the result of the fine dispersed second phase particles. {001} texture was absent in the whole thickness of all the annealed IF steels. In addition, the strongest γ texture was found, and this was a potential way to improve the deep drawability of annealed steel sheets.

Abstract: In this paper, I+II mixed mode notch-crack fatigue propagation in titanium alloy steel TA2 was tested with the emphasis on the crack mode transition and retardation under constant amplitude loading or overloading. Finite element method was employed to calculate the stress distribution at the crack tip in order to explain the crack growth behavior. It is found that after initiation from the crack tip, the new formed crack propagates in a mode I form, regardless of the magnitudes of the inclined angle of the crack and the overloading applied. The relationship between the fatigue crack growth rate and mode I stress intensity factor range was calculated. After overloading, crack initiation and propagation will be significantly slowed, or in other words, there exists overloading retardation. Calculation shows that after overloading, a plastic zone with residual compressive stress is formed which is responsible for the retardation of the crack growth rate. Micro-morphologies of the crack growth path and the crack fracture surface were also observed and analyzed.

Abstract: Strengthening of aluminum alloy has always been an interesting research topic. There might be interactions between different strengthening mechanisms. In this paper, the effect of large cold deformation on the precipitation of as-quenched 7050 aluminum alloy was studied. Differential scanning calorimetry was used as the main research technique, accompanied by tensile test and transmission electron microscopy. It was found that clusters and precipitation had formed in the cold deformation, and dislocations accelerated the precipitation dynamics.

Abstract: In this study, the inhomogeneous properties and microstructure at typical position of an Al-7.5Zn-1.6Mg-1.4Cu-0.11Zr alloy forging in T7452 condition have been investigated using OM, SEM, TEM and EBSD analysis, tensile properties testing, conductivity measurement and fracture toughness testing. The results indicate that wherein the properties near the surface layer and in the core of the alloy forging exhibit a difference of 10% or more. There are obvious differences in grain morphology, quench-introduced precipitation and recrystallization degree in the two positions. Due to the high quenching temperature, there appears a heavy quench-introduced precipitation phenomenon in the core more than surface layer of the alloy forging, which improves the electrical conductivity, but significantly reduces the strength of the final material. And there is a higher proportion of the recrystallization organization in the core of the alloy forging, seriously affecting its elongation and fracture toughness. Microstructure inhomogeneity of the alloy forging determines the uniformity of its properties.

Abstract: An investigation for the cracking mechanism of a 304 stainless steel flange was carried out. The flange was installed in a (NH₄)₂SO₄ tank . Optical microscopy examination shows that the cracking is intergrainular. SEM examination shows that the brittle nature of the cracked surface morphology. EDS analysis shows that chloride exists on the cracked surface. Electrolytic etching of the stainless steel in oxalic acid solution reveals that it has intergrainular corrosion sensitivity. The results show that poor welding operation caused to form defects in the weld. Corrosion occurred preferentially in the defect area and cracks propagated circumferentially in the weld seam. The crack propagation direction changed at a point where there was a large circumferential stress.

Abstract: The experiments were simulated based on the real environment of The East China sea. It were conducted to study HAZ seawater corrosion behaviors as well as effect of welding process on the corrosion performance of 304 stainless steel at different welding processes of argon arc welding with electrochemical technology. The results indicated that when the welding current increases, the corrosion rate of stainless steel sample will also increase while the open circuit potential will decrease. And with the increasing argon flow rate , the results will completely be opposite. The largest impedance size of the parent metal is 36.175 Ω/ cm² and the minimum impedance size of B1R is 12.531 Ω/ cm².

Abstract: We chose cast and extrude magnesium alloy AZ61 as materials and studied the influences of temperature, humidity, pressure and NaCl atmosphere on the corrosion products and corrosion mechanism by means of SEM, EDS and XRD. we could indicate the corr osion rate of extruded AZ61 magnesium is faster than that of cast AZ61 magnesium. Both th e rearrange of second ph ase and smaller grain size, which owing to the extrusion process, change the morphologies of corrosion products.

Abstract: Based on Pham’s model, the non-isothermal ferrite transformation start temperature and time of Fe-C-Mn-Si alloys were deduced. The parameters of expression were predicted combined with experimental results. The relationship between ferrite transformation parameters Q , C and composition of Fe-C-Mn-Si alloys was obtained. Then the ferrite transformation start curve of Fe-C-Mn-Si alloys can be accurately predicted by the computational method, which can be extended to more complex multi-component alloy systems.

Abstract: he effect of pass deformation on the microstructure of Al-Mg-Sn-Bi-Ga-In alloy anode was investigated by using SEM, TEM, and EBSD. The results show that when controlling the rolling deformation at 40%, the segregation phases on the Al alloy matrix was the best distributed for the reason of dynamic recrystallization procedure. The electrochemical and anti-corrosion results show that uniform distribution of segregation phase will improve the related properties of Al alloy anode. After optimizing the rolling procedure, the Al alloy anode has more negative electrode potential of about -1.585V(vs.Hg/HgO) and lower hydrogen evolution rate of 0.092mL/ (min·cm2)

Abstract: The mechanical properties and corrosion behaviors of the casting Al-Cu alloys were investigated. The proportion of the two modifiers (PrxOy and LaxOy) has effects on the mechanical properties and the electrochemical corrosion behavior of the casting Al-Cu alloy. The ultimate true tensile strength of the Al-Cu alloy modified only by LaxOy is the highest (616.0 MPa). The fracture strain of the Al-Cu alloy modified by PrxOy and LaxOy is the highest (12.3%). The Al-Cu alloy modified by PrxOy has better corrosion resistance than any other Al-Cu alloy. The prominent mechanical properties should be attributed to the finer crystal grains and more homogeneously distributed nano-scale phase precipitates. The existence of continuous and compact protective Al2O3 and RE-O films enhanced the corrosion resistance of the modified Al-Cu alloy during the corrosion process.