Grain refining technique of AM60B alloy by Al-Ti-B master alloy

The effects of grain refining parameters on grain size of AM60B magnesium alloy have been investigated using an Al-5Ti-IB master alloy as refiner; and an appropriate refining technique has been developed. The results indicate that the Al-Ti-B master alloy is an effective grain refiner for AM60B alloy and the grain size can be decreased from 348 μm to 76 μm. Raising the addition temperature or the poudng temperature is beneficial for grain refinement; while for the addition amount and holding time, there is an optimal value. The appropriate grain refining technique is that 0.3% Al-Ti-B master alloy is added at 780℃ and then the melt is held for 30 min before pouring. The above phenomena can be explained by the refining mechanisms that have been proposed from the related studies on Al and Mg alloys and theoretical analysis.

STUDY OF THE NUCLEATION MECHANISM OF α-Al GRAINS AFTER ADDITION OF Al-Ti-B MASTER ALLOYS

Nucleation sites of α-Al grains after addition of an Al-Ti-B master alloy into pure aluminium have been investigated using EPMA. The results show that either TiAl3 or boride particales can nucleate α-Al grains. But the number of TiAl3 nucleants is reduced with the holding time prolonged and the boride-nuclei are increasing gradually. Based on these results, a new refining method, adding molten Al-Ti-B into commercially pure aluminium, which has a quicker and better refining efficiency is presented.

Influence of forming process on three-dimensional morphology of TiB_2 particles in Al-Ti-B alloys

A series of Al-Ti-B master alloys were prepared by different preparation routes,and the TiB2 particles in the master alloys were extracted and analyzed.It is found that the forming process has significant influence on the three-dimensional morphology of TiB2 particles.Different preparation routes result in different reaction forms,which accounts for the morphology variation of TiB2 particles.When the Al-Ti-B master alloy is prepared using ＂halide salt＂ route,TiB2 particles exhibit hexagonal platelet morphology and are independent with each other.In addition,the reaction temperature almost does not have influence on the morphology of TiB2 particles.However,TiB2 particles exhibit different morphologies at different reaction temperatures when the master alloys are prepared with Al-3B and Ti sponge.When the master alloy is prepared at 850 ℃,a kind of TiB2 particle agglomeration forms with a size larger than 5 μm.The TiB2 particles change to layered stacking morphology even dendritic morphology with the reaction temperature reaching up to 1200 ℃.

Influence of Al-Ti-B addition on the microstructure and mechanical properties of A356 alloys

The mechanical properties (σb,σ0.2,and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%,the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also,they display exc...

Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys

Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.

Preparation of V-Ti-Fe master alloys by metallothermic reduction method

V-Ti-Fe master alloys were prepared by metaUothermic reduction method, and the influences of the mass ratio of V205 to TiO2, Al and Al-Mg alloy addition amounts on the metal recovery rates and alloy compositions were investigated. The results show that appropriate technological parameters are： the mass ratio of V205 to TiO2 is 0.5：1, Al addition represents 95% of the theoretical value, and the Al-Mg alloy addition amount is one third that of the Al addition. The results from energy spectrum analysis show that V and Fe distribute uniformly in the prepared alloy, while the segregation for Ti, i.e. Ti-rich phase is detected. A spray refming process was carried out to reduce the impurity contents of Al and O in the prepared alloys. The Al content drops from 4.27% to 1.86%, and the O content drops from 2.10% to 0.91% after the refining process.

Grain refinement mechanism of Al-5C master alloy in AZ31 magnesium alloy

Al-5C master alloy was prepared by powder in situ synthesis process, and its effects on grain refinement of AZ31 alloy and refining mechanism were investigated. The results indicate that the AI 5C master alloy consists of a（Al） and A14C3 phases, and the size distribution of Al4C3 particles is controlled by sintering time. The AI 5C master alloy can remarkably reduce the grain size of AZ31 alloy, which decreases with the increasing addition amount of AI-SC master alloy when the addition amount is below 2%. The refining mechanism is attributed to the formation of new compounds of Al-C-Mnparticles by Al4C3 and Mn, which might act as nucleating substrates for a-Mg grain.

Influence of Al-Mn master alloys on microstructures and electrochemical properties of Mg-Al-Pb-Mn alloys

Mg-Al-Pb alloy is one of the newly developed materials for the seawater activated batteries. As-cast Mg-6Al-5Pb and Mg-6Al-5Pb-0.5Mn alloys with different additions of Al-15%Mn （mass fraction）, Al-30%Mn and Al-50%Mn master alloys were prepared by melting and casting. Their microstructures were observed by optical microscopy and scanning electron microscopy. The electrochemical properties, hydrogen evolution and mass loss of Mg-6Al-5Pb-0.5Mn alloys were studied. The results show that Mg-6Al-5Pb-0.5Mn alloy added with Al-50%Mn master alloy provides more negative corrosion average potential （-1.66 V）, smaller corrosion current density （7 μm/cm2） and lower free corrosion rate （0.51 mg·cm-2·h-1） than other alloys. This is probably attributed to the presence of Al11Mn4 phase, which facilitates the self-peeling of corrosion products and enlarges the electrochemical reaction area as well as enhances the electrochemical activity.

Microstructure evolution of Al-Sr master alloy during continuous extrusion

The microstructure evolution of Al–Sr master alloy during continuous extrusion was investigated using X-ray diffractometer, scanning electron microscope and transmission electron microscope. Results indicate that the continuous extrusion process could change the Al4Sr particles of the alloy significantly in size and morphology. The as-cast needle-like Al4Sr particles are broken into small blocks in upsetting zone and crushed heavily in adhesion zone. Plenty of dislocations get tangled up in right-angle bending zone. Al4Sr particles grow in the extending zone. Finally, Al4Sr particles in products are approximately 28 μm in length. Al2Sr particles precipitate during the process. Compared with products by horizontal extrusion, Al4Sr particles by continuous extrusion are finer and distribute more evenly.

Effect of cooling rate on morphology of primary particles in Al-Sc-Zr master alloy

Al-1.0%Sc-1.0%Zr （mass fraction） master alloy was prepared at different cooling rates. The morphology and thermodynamics data of the primary particles of the master alloy were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and differential scanning calorimetry （DSC）. It shows that the primary particles are dendrite-shaped particles comprised of several attached small cubic, cusped-cubic or crucifer shape particles at slow cooling rate. However, the primary particles are separated with crucifer shape at intermediate cooling rate, and they are cubic with cusped-cubic shape at high cooling rate. Meanwhile, the separated and attached particles present AlaSc/AlaZr1-xScx core-shell structure. The formation mechanism of the structure was systematically investigated by a mathematical model.

Production of Al-B master alloys by mixing KBF_4 salt into molten aluminum

Two mixing techniques,the immersion method and the vortex method,were adopted in the production of Al-3%B master alloys since the generally used production route involving the direct addition of KBF4 salt to molten aluminum has several drawbacks.The experimental results demonstrate that the Al-B master alloys produced by the immersion method show a microstructure characterized by the appearances of AlB12 phase and many agglomerations of boride particles,while the Al-B master alloy produced by the vortex method exhibits a well dispersed microstructure of AlB2 particles in the matrix.The distinct microstructure features result from the differences in the stirring speed during the salt additions and the average size of the salt droplets achieved by the salt additions.

Grain refining effect of Mg by novel particle cluster-containing Al-Ti-C master alloy

A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed crystal with a diameter of （110-a：17） ~tm. The results indicate that A14C3 and TiC particle cluster, rather than a single particle, plays an important role in the refining process. Compared with the simplex smooth nucleating substrate, concave regions on the particle cluster provide easier route for the transformation from liquid Mg atoms to stable nucleus. Nucleus with a small size can also reach the critical nucleation radius when they attach on the concave regions of the substrate. A14C3 and TiC particle clusters thus become more favorable nucleating substrate for a-Mg grains.

Al-Si-P master alloy and its modification and refinement performance on Al-Si alloys

An Al-Si-P master alloy has been developed by an in-situ reaction and the electron probe microanalyzer （EPMA） results show that there are many pre-formed AlP particles contained in the master alloy. Silicon introduced into the system plays an important role in remarkably improving the distribution and content of AlP particles due to their similar crystal structure and lattice parameters. ZL109 alloys have shown fast modification response to the addition of 0.5% Al-15Si-3.5P master alloy at 720℃, with a mass of primary Si precipitating in size of about 15 μm. Also, coarse primary Si grains in AI-30Si alloy can be refined dramatically from 150 μm to 37 μm after the addition of 2.0% Al-15Si-3.5P master alloy at 850℃. The P recovery of the Al-15Si-3.5P master alloy is much higher than that of a Cu-8.5P master alloy due to the pre-formed AlP particles.

Role of C and Fe in Grain Refinement of an AZ63B Magnesium Alloy by Al-C Master Alloy

In this study, grain refining effect of Al-1.5℃ master alloy was examined on an AZ63B magnesium alloy, and the refining mechanism was studied through investigating the role of C and Fe in this process. The results show that addition of Al-1.5℃ master alloy leads to significant decrease of the mean grain size from about 270μm to 50μm at the center of the AZ63 alloy ingot. Grain refinement by carbon addition is mainly due to the heterogeneity nucleation on the Al-, C-, O-, Fe- and Mn-rich particles, but not constitutional undercooling caused by the carbon solute element. Fe plays an important role in the formation of the nucleating particles, but not acts as an inhibiting element.

Preparation of Al-Sr Master Alloy in Aluminum Electrolysis Cell

Al Sr master alloy was prepared by using liquid aluminum cathode and a mixture of Na 3AlF 6 - SrCO 3 as the basic molten salt electrolyte in a laboratory electrolysis cell.The effects of electrolyte composition,electrolysis temperature,cathodic current density and the electrolytic duration on Sr content of Al Sr alloy were studied.Through laboratory experiments,the parameters for smooth electrolytic reaction were proposed.

Refinement of primary Si in Cu-50Si alloys with novel Al-Zr-P master alloy

In this article, a novel Al-6Zr-2P master alloy with ZrP particles was successfully synthesized, and the refining performance of this novel master alloy for the primary Si in Cu-50Si alloys was also investigated. By means of the fracture plane observation, it is found that the ZrP phase would precipitate first in the solidification pro- cess, and then, the ZrAl3 phase grows around them. Fur- thermore, it is observed that the refining effect can be remarkably improved by changing the addition sequence of the raw materials. After the melting of commercial Cu, the 2.0 wt% Al-6Zr-2P master alloy and crystalline Si were added in sequence, and the mean size of the primary Si in Cu-50Si alloy can be significantly refined from 255.7 to 75.3 gm. Meanwhile, the refining mechanism was dis- cussed in detail.

INFLUENCE OF Al-5Ti-1B MASTER ALLOY ON MICROSTRUCTURE AND DAMPING CAPACITY OF ZA27 ALLOY

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Influences of Preparation Conditions and Melt Treatment Procedures on Melt Treatment Performance of Al-5Ti-B and Al-10Sr Master Alloys

The influences of preparation conditions of Al-5Ti-B （as-cast and hot-rolled） and Al-10Sr （as-cast and hotextruded） and melt treatment procedures on the grain refinement and modification performance of A356 alloy are experimentally studied. For the two master alloys, the 50% reduction is sufficient to meet the demands of the efficient grain refinement and modification of A356 alloy. When Al-STi-B is introduced into the melt prior to degassing, the grain refinement efficiency of Al-5Ti-B will be greatly increased due to the better dispersity of TiB2 particles. Al-5Ti-B master alloy is less prone to affect the modification effect of Al-10Sr when they are used together.

Refining Effect of a New Al3Ti1B1RE Master Alloy on Al Sheets Used for Can Manufacture and Behavior of Rare Earths in Master Alloy

The refining effect of Al3Ti1B1RE master alloy on Al sheets used for pressure can manufacture and the behavior of mixed rare earths in master alloy were investigated with XRD, OM, SEM and EDAX. It is found that the refining effect of the refiner on the material has superiority over foreign or domestic Al5Ti1B refiner, and the refiner still retains its refining ability for 6 h after adding it to molten Al, thus improving the strength and plasticity of the material remarkably. The excellent refining effect and stability of AlTiBRE refiner result from that RE can lower the surface energy of molten Al and improve the wetting characteristics of molten Al on refinement nuclei such as TiAl 3, TiB 2, etc., thus giving full play to the effect of heterogeneous nucleation and impeding the congregating tendency of TiB 2 phase in molten Al. At the same time, RE gathering in front of solid/liquid interface are also easy to cause composition supercooling in molten Al, thus impeding the growth of α Al grains and promoting α Al nucleation on refinement nuclei. In addition, RE also play certain role in purification and grain refinement, or modification, especially their effect of purification can improve the metallurgical quality of AlTiBRE master alloy.

Effect of cooling rate on morphology and type of vanadium-containing phases in Al-10V master alloy

Effects of cooling rates on the morphology, sizes and species of primary vanadium-containing phases in Al-10V master alloys were investigated. The results show that the primary vanadium-containing phases with different morphologies and compositions present in Al-10V master alloys at different cooling rates with the pouring temperature of 1,170 °C. When the Al-10V master alloy is solidified in the refractory mold at a cooling rate of 2 °C·s-1, the vanadium-containing phases are mainly plate-like Al10V phases, with the average size of 100.0 μm in the center and 93.2 μm at the edge of the ingot. When the master alloy is solidified in the graphite mold at a cooling rate of 24.3 °C·s-1, the primary vanadium-containing phases are dendritic Al3V phases, with the average length of 297.0 μm for the first dendrite in the center and 275.0 μm at the edge of the ingot. The secondary dendrite arm spacing (SDAS) is 9.5 μm in the center and 9.3 μm at the edge of the ingot, respectively. When the solidification is carried out in the copper mould at a cooling rate of 45.7 °C·s-1, the primary vanadium-containing phases are also Al3V phases but with smaller size, compared with that prepared at the cooling rate of 24.3 °C·s-1. As a result, the average length is 190.0 μm for the first dendrite in the center and 150.0 μm at the edge of the ingot. The SDAS is 9.8 μm in the center and 4.4 μm at the edge of the ingot, respectively.