Effect of CeO2 Size on Microstructure, Synthesis Mechanism and Refining Performance of Al-Ti-C Alloy.

The effects of CeO2 size on the microstructure and synthesis mechanism of Al-Ti-C alloy were investigated using a quenching experiment method. A scanning calorimetry experiment was used to investigate the synthesis mechanism of TiC, the aluminum melt in situ reaction was carried out to synthesize master alloys and its refining performance was estimated. The results show that the Al-Ti-C-Ce system is mainly composed of α-Al, Al3Ti, TiC and Ti2Al20Ce. The addition of CeO2 obviously speeds up the progress of the reaction, reduces the size of Al3Ti and TiC and lowers the formation temperature of second-phase particles. When the size of CeO2 is 2-4 µm, the promotion effect on the system is most obvious. The smaller the size of CeO2, the smaller the size of Al3Ti and TiC and the lower the formation temperature. Al-Ti-C-Ce master alloy has a significant refinement effect on commercial pure aluminum. When the CeO2 size is 2-4 µm, the grain size of commercial pure aluminum is refined to 227 µm by Al-Ti-C-Ce master alloy.

Hot Deformation Behavior and Microstructure Evolution of 6063 Aluminum Alloy Modified by Rare Earth Y and Al-Ti-B Master Alloy.

The hot deformation behaviors of the new 6063 aluminum alloy modified by rare earth Y and Al-Ti-B master alloy were studied through isothermal hot compression experiments on the Gleeble-3800 thermal simulator. By characterizing the flow curves, constitutive models, hot processing maps, and microstructures, we can see from the true stress-true strain curves that the flow stress decreases with the increase of deformation temperature and the decrease of strain rate. Through the calculation of the constitutive equation, we derived that the activation energy of the new composite modified 6063 aluminum alloy is 224.570 KJ/mol. we roughly obtained its excellent hot processing range of temperatures between 470-540 °C and the strain rates of 0.01-0.1 s-1. The verification of the deformed microstructure shows that with the decrease of lnZ, the grain boundary changes from a low-angle one to a high-angle one and the dynamic recrystallization is dominated by geometric dynamic recrystallization and continuous dynamic recrystallization. Analysis of typical samples at 480 °C/0.01 s-1 shows that the addition of rare earth Y mainly helps form Al3Y5 and AlFeSiY phases, thus making the alloy have the performance of high-temperature recrystallization, which is beneficial to the hot workability of the alloy.

Investigation of Microstructure of Al-5Ti-0.62C System and Synthesis Mechanism of TiC.

Al-Ti-C master alloys have been widely investigated by various researchers. However, their refining effectiveness is still severely compromised by the preparation process. In this work, the aluminum melt in-situ reaction was carried out to synthesize the Al-5Ti-0.62C, and its refining performance was estimated. The thermodynamics calculation and differential scanning calorimeter experiment were used to investigate the synthesis mechanism of TiC. Quenching experiment was conducted to explore phase and microstructure transformation of the Al-5Ti-0.62C system. The results show that the main phases of Al-5Ti-0.62C master alloys are α-Al, Al3Ti, and TiC and it has a positive effect on commercial pure aluminum refining. Commercial pure aluminum is completely refined into the fine equiaxed structure by adding 0.3% Al-5Ti-0.62C master alloy. TiC particles mainly distribute in the grain interior and grain boundaries. The excess Ti came from the dissolution of Al3Ti spreading around TiC and finally forming the Ti-rich zone to promote the nucleation of α-Al. The experiments certified that TiC was formed by the reaction between solid C and excess Ti atoms. The main reactions in the Al-5Ti-0.62C system were that solid Al is transferred into liquid Al, and then liquid Al reacted with solid Ti to form the Al3Ti. At last, the release of a lot of heat promotes the formation of TiC which formed by the Ti atoms and solid C.

Viscosity and Structure of a CaO-SiO2-FeO-MgO System during a Modified Process from Nickel Slag by CaO.

There is a high iron content in nickel slag that mainly exists in the fayalite phase. Basic oxide can destroy the stable structure of fayalite which is beneficial to the treatment and comprehensive utilization of nickel slag. The research was based on the composition of the raw nickel slag, taking the CaO-SiO2-FeO-MgO system as the object and CaO as a modifier. The effect of basicity on the melting characteristics, viscosity and structure of the CaO-SiO2-FeO-MgO system was studied. The relationship between the viscosity and structure of the CaO-SiO2-FeO-MgO system was also explored. The results show as follows: (1) When the basicity is lower than 0.90, the primary phase of the slag system is olivine phase. When the basicity is greater than 0.90, the primary phase of the slag system transforms into monoxide. When the basicity is 0.90, olivine and monoxide precipitate together as the temperature continues to decrease. At the same time, the liquidus temperature, softening temperature, hemispherical temperature, and flow temperature all reach the lowest value. (2) With the increase of basicity, the critical viscosity temperature of the CaO-SiO2-FeO-MgO system decreases first and then increases. Critical viscosity temperature is the lowest at the basicity of 0.90, which is 1295 °C. (3) When the slag system is heterogeneous, the viscosity of the molten slag increases rapidly because of the quantity of solid phase precipitated from the CaO-SiO2-FeO-MgO system. (4) When the slag system is in a homogeneous liquid phase, the molar fraction of O0 decreases with the increase of basicity and the mole fraction of O-, and O2- increases continuously at the basicity of 0.38~1.50. The silicate network structure is gradually depolymerized into simple monomers, resulting in the degree of polymerization, and the viscosity, being reduced. The mole fraction of different kinds of oxygen atoms is converged to a constant value when the basicity is above 1.20.

Effect of Micro-Scale Er on the Microstructure and Fluidity of ZL205A Alloy.

The effect of Er addition on the fluidity and microstructure transformation of the as-cast and T5 heat-treated ZL205A alloys was investigated by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The fluidity of the liquid metal after adding Er was tested and the fracture characteristics of the material were analyzed. The results indicated that Er was mainly dissolved into an α-Al matrix near the grain boundaries (GBs). It is easily segregated and enriched in the intersection of the GBs or the interface between the α and θ phase, which caused the intermetallic compounds to be distributed along the GBs to the neck and to fuse. Er could also inhibit the diffusion of Cu atoms in the process of solid solution, so that increased the residual eutectic structures in the crystal, while accelerating the precipitation progress of the Guinier-Preston (GP) zone and θ' phase and increasing precipitation of the θ phase. A small amount of precipitation of θ phase and micro-scale Er (0.1-0.5 wt %) can significantly increase the fluidity and reduce the casting defects, which can effectively improve the castability of the ZL205A alloy. The interface between the (Al8Cu4Er) phase and matrix is the main area of microcracks, through analyzing the fracture morphology.

Effect of CeO2 on Microstructure and Synthesis Mechanism of Al-Ti-C Alloy.

The effects of CeO2 on the microstructure and synthesis mechanism of Al-Ti-C alloy were investigated by quenching experiment method, while using Al powder, Ti powder, graphite powder, and CeO2 powder as main raw materials. The results showed that the addition of CeO2 was favorable for promoting the formation of TiC particles in Al-Ti-C systems. With CeO2 contents increasing, the distribution of TiC particles were more homogeneous, and the rare earth phase Ti2Al20Ce was formed. CeO2 had little effect on the synthesis of Al3Ti particles in Al-Ti-C systems, but had a significant effect on the synthesis of TiC particles. In the Al-Ti-C system, TiC is mainly formed by the reaction of dissolved [Ti] and solid C in the melt. While in the Al-Ti-C-Ce system, CeO2 reacts with C and O2 to form CeC2 firstly, and then CeC2 reacts with dissolved [Ti] to form TiC. Based on thermodynamic calculation and microstructure analysis in the process of reaction, a macroscopic kinetic model of Al-Ti-C-Ce system reactions was proposed in this paper.

Effect of Al-5Ti-C Master Alloy on the Microstructure and Mechanical Properties of Hypereutectic Al-20%Si Alloy.

Al-5Ti-C master alloy was prepared and used to modify hypereutectic Al-20%Si alloy. The microstructure evolution and mechanical properties of hypereutectic Al-20%Si alloy with Al-5Ti-C master alloy additions (0, 0.4, 0.6, 1.0, 1.6 and 2.0 wt%) were investigated. The results show that, Al-5Ti-C master alloy (0.6 wt%, 10 min) can significantly refine both eutectic and primary Si of hypereutectic Al-20%Si alloy. The morphology of the primary Si crystals was significantly refined from a coarse polygonal and star-like shape to a fine polyhedral shape and the grain size of the primary Si was refined from roughly 90-120 µm to 20-50 µm. The eutectic Si phases were modified from a coarse platelet-like/needle-like structure to a fine fibrous structure with discrete particles. The Al-5Ti-C master alloy (0.6 wt%, 30 min) still has a good refinement effect. The ultimate tensile strength (UTS), elongation (El) and Brinell hardness (HB) of Al-20%Si alloy modified by the Al-5Ti-C master alloy (0.6 wt%, 10 min) increased by roughly 65%, 70% and 51%, respectively, due to decreasing the size and changing the morphology on the primary and eutectic Si crystals. The change in mechanical properties corresponds to evolution of the microstructure.

Performance Comparison of Al-Ti Master Alloys with Different Microstructures in Grain Refinement of Commercial Purity Aluminum.

Three types of Al-5Ti master alloys were synthesized by a method of thermal explosion reaction in pure molten aluminum. Performance comparison of Al-5Ti master alloy in grain refinement of commercial purity Al with different additions (0.6%, 1.0%, 1.6%, 2.0%, and 3.0%) and holding time (10, 30, 60 and 120 min) were investigated. The results show that Al-5Ti master alloy with blocky TiAl3 particles clearly has better refining efficiency than the master alloy with mixed TiAl3 particles and the master alloy with needle-like TiAl3 particles. The structures of master alloys, differing by sizes, morphologies and quantities of TiAl3 crystals, were found to affect the pattern of the grain refining properties with the holding time. The grain refinement effect was revealed to reduce markedly for master alloys with needle-like TiAl3 crystals and to show the further significant improvement at a longer holding time for the master alloy containing both larger needle-like and blocky TiAl3 particles. For the master alloy with finer blocky particles, the grain refining effect did not obviously decrease during the whole studied range of the holding time.