Papers by Keyword: Solidification Structure

Abstract: This paper mainly studies the composition of strengthening phase, characteristic precipitation temperature and composition range of strengthening phase in Ti-Al-Mo-Zr-Si medical titanium alloy, and the influence of element changes on the content and microstructure of strengthening phase. Promote the formulation of thermodynamic process of titanium alloy powder metallurgy, as well as the formulation of alloy hot working and solid solution aging process. In this paper, Panda thermodynamic software is used to calculate the multicomponent alloy thermodynamics and multicomponent phase diagram of titanium alloy materials. The effects of Al, Mo, Zr, Si and other elements on the precipitation of strengthening phase and the phase transformation content of solidification structure were obtained. It is found that the content of Mo is more than 2 wt.% β phase transition precipitation angle. Meanwhile, in order to avoid the excess of precipitates such as Mo5Si3 and M3Si, the content of Mo should be less than 4.6 wt.%. The content of Zr can be maintained at about 1.5 wt.%. If the aging precipitation of the material is considered, it can be controlled to be less than 2 wt.%. The content of this paper is the basis and improvement of titanium powder metallurgy technology and rapid prototyping technology.

Abstract: Taking high power density M142 piston aluminum alloy as the main research object, this paper studies the changes of element contents such as Si, Fe and Cu, as well as the effects on the precipitation strengthening phase sequence, type and phase transformation. Based on the phase diagram and thermodynamic calculation results of multicomponent alloys between different elements, the phase transformation in the solidification process of the alloy, as well as the temperature and composition window of each phase transformation were studied. Especially in alloys ε Phase (Al3Ni), δ Phase (Al3CuNi), and γ phase (Al7Cu4Ni). The thermodynamic conditions for the formation of nickel rich heat-resistant phases. At the same time, the effects of the contents of Cu, Fe and other elements on the solidification structure were studied. The optimum composition, temperature, pressure and other process parameters of the alloy were optimized. At the same time, it is analyzed and verified in combination with relevant metallographic photos to deeply understand and master the composition design and preparation process of the alloy.

Abstract: Effects of Cerium (Ce) addition on solidification structure of a low-carbon 42CrMo4 steel was investigated. The addition of up to 0.067 wt.% of Ce in the steel produced greatly improved solidification structure with a suppressed columnar grain zone, finer grain size in an equiaxed grain zone and zero area fraction of casting shrinkage cavity. The added Ce occurred in the steel both in the form of Ce oxy-sulfide inclusions and as dissolved atomic Ce segregated together with other elements at prior austenite grain boundaries and at interdendritic spacing. The Ce oxy-sulfide inclusions were found to play a major role in the observed improved grain structure meanwhile dissolved Ce had pronounced effects on morphology of dendritic networks. The fraction of Ce dissolved in the melt appeared to bring about increase in fluidity of the molten steel, leading to total elimination of interdendritic shrinkage porosity in solidification structure of the steel with added Ce. Ce addition can be considered as a potential solution for grain structure refinement in heavy-weight castings of 42CrMo4 steel grade.

Abstract: This paper uses ProCast software to simulate Mg-Gd alloy solidification process, calculates temperature field and solidification field for Mg-9.76Gd at different stages and compares the influence of different heat transfer coefficient on the solidification structure. The results show that the crystallization process which is simulated is consistent with the actual crystallization process; as the heat transfer coefficient increases, the average grain size decreases. With the result, the reasonable casting formation control parameters can guide the practical production, which can reduce human and financial resources.

Abstract: The influences of pulsed magnetic field (PMF) on solidification structure of 6063 alloy were studied in this article. The results show that solidification structure of 6063 alloy can be refined with the application of PMF. The dendrite growth restrained and the macrostructure changed from large dendrite grains to fine equiaxed grains. The grain size decreased when the voltage increased from 0V to 600V. However, when the pulse frequency increased from 5Hz to 15Hz, the average grain size decreased continuously until reached a limit, and then the grains coarsened with further increase of the pulse frequency. The vibration caused by PMF not only made the temperature field of the melt uniform ,but also brook off the initial solidified grains formed on the cold wall of the mold, and spurs the grains to move to the center of melt which can be acted as nuclei.

Abstract: It is investigated that effect of steel strip-feeding ratio and superheat degree of molten steel on solidification structure of ingot by the steel strip-feeding experiment in the mold. The results show that: at the same superheat, with the increase of feeding ratio, the area proportion of equiaxed grain zone increases and the average size of equiaxed grain decreases, and at the same feeding ratio, the higher the superheat is, the smaller the proportion of equiaxed grain zone is, and the larger the average grain size is.

Abstract: In this work, the meaning of the solidification structure and how it is related to defect formation in grey cast iron will be discussed. The work also confirms observations made earlier. In previous work the formation of shrinkage porosity in grey cast iron cylinder heads was investigated. It was found that the defect is located around solidification units resembling primary austenite grains. The solidification of grey cast iron starts with the formation of primary austenite grains, followed by the eutectic solidification. The primary grains nucleate and grow either as columnar or equiaxed grains, creating a columnar to equiaxed transition between the two zones. Based on the presence of a migrating hot spot, and other characteristics found on the cylinder heads, a geometry was developed that promote the formation of shrinkage porosity. The primary solidification structure, normally transformed during the solid state transformation, was preserved using a technique called Direct Austempering After Solidification (DAAS). After solidification, the samples were cut and prepared for investigation using a Scanning Electron Microscope (SEM) equipped with a detector for Electron Back Scattered Diffraction (EBSD). Individual grains were identified and the primary solidification structure around the defects was revealed. The investigation shows how shrinkage porosity is formed and located between primary austenite grains. This confirms that the primary solidification structure has a large influence on the formation of defects in grey cast iron. The investigation also confirms the correctness of earlier results as well as the validity of the DAAS technique.

Abstract: In this paper, effects of different grain refiners on solidification structure of H62 brass under different cooling rates were investigate by macro corrosion, SEM and EDX analyses. Results of experiments indicate that the columnar crystal zone of H62 brass is completely eliminated and the grain size is reduced remarkably by 0.01%B. It has been found that the columnar grain zone is also eliminated by 0.1Ti, 0.1Zr, 0.1Ti+0.1Zr and 0.1Ti+0.1Zr+0.01B additions, respectively, but their grain refining effects are not as good as 0.01B. The grain size of H62 ingot with 0.1Ti addition prepared by sand mold casting is coarser than prepared by permanent mould casting. The microstructures of as cast H62 alloy are composed of α dendrite phases and rodlike β' phases which enrich on grain boundary to form an array structure.

Abstract: Thermal flow finite element simulation was carried out to deeply understand the solidification and deformation phenomena of magnesium alloy in molten zone during twin-roll casting process. The results show that temperature near the nip of the rolls is about 680K based on current conditions, and there are two vortexes in the molten pool during casting, a peak formed at solidus. Due to the metal flows in molten pool and relative rotates of the rolls, temperature field of molten zone is different from normal casting, which will cause the solidification structure changes. An experiment by using a vertical type twin-roll caster was also conducted, and the amount of deformation bands at the joint line is larger than that at the two sides. Substructures can be found due to dynamic recrystallization during casting process.

Abstract: It has analyzed that there is no difference between positive and radial pressure of the interior of multi-directional squeeze casting solidified body. The isotropy of pressure makes the consistency of heat exchange coefficient of interface, crystalline growth velocity and plastic deformation, which thereby enables the solidification structure form of multi-directional squeeze casting parts to eliminate the defects of directional difference of single axis squeeze and non-uniformity of density. It has put forward that multi-directional squeeze casting technique shall be adopted for producing high-performance casting parts with uniform structure property and high density.