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.

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.

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.

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.

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.

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.

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.

Quality assessment of aluminum-based grain refining master alloys

Based on some theoretical and practical approaches, the main stages of the quality assessment of aluminum-basedgrain refining master alloys have been revealed. Methods for the quality improvement of Al-Ti and Al-Ti-B grain refinershave been described.

Effect of Al-TiB master alloy addition on microstructure, wear and compressive deformation behaviour of aluminum alloys

Aluminum-10% TiB master alloy was added in various proportions in 7178 Al alloy in order to examine the effect of TiB on grain refinement, wear and compressive deformation of the later one. Microstructural characterization reveals that TiB particles act as grain refiners for primary base alloy and result in globular dendrites. It was observed that the wear resistance and strength of the alloy decreased when the master alloy addition increased beyond 20%, even though the dendrites become much finer and almost spherical in nature.

A new development of Al-Ti-C grain refining master alloys

Al Ti C master alloys have been prepared with a novel production method. A combination of X ray phase analysis, SEM and EDS was used to examine the phases and microstructures of the master alloys. The master alloys have block like Al 3Ti particles and submicron size TiC X with X ranging from 0.49 to 0.78 and show excellent grain refining performance for commercially pure aluminum. Titanium carbides were observed at the crystallization centers in refined castings.

Effect of Al5Ti1B master alloy on microstructures and properties of AZ61 alloys

AZ61 alloys with different levels of Al5Ti1B master alloy additions were prepared by conventional casting method.The effects of Al5Ti1B contents and holding time on microstructures and microhardness of AZ61 alloys were studied by XRD,OM and microhardness testing techniques.The results show that when the addition level of Al5Ti1B master alloy is less than 0.5%(mass fraction),the average grain size of the alloys decreases with the increase of Al5Ti1B content at the same holding time.But the grain size increases somewhat with further addition of Al5Ti1B.The average grain size of the alloys decreases with the increase of the holding time as it is less than 30 min at the same addition level of Al5Ti1B.It is considered that TiB2 particles can serve as the heterogeneous nucleation sites ofα-Mg during solidification,and heterogeneous nucleation is the main reason for the grain refinement of AZ61 alloys.The microhardness of the refined AZ61 alloys with 1.0%Al5Ti1B addition is increased by about 8%.

Effect of AlP master alloy on grain refinement of primary silicon in eutectic Al-Si alloys

To obtain the finer primary silicon crystals, the proprietary Al-P masteralloy was adopted to modify the eutectic Al-Si alloys and the most suitable modification process wasmade in the experiments. The SEM (Scanning Electron Microscope) and DSC (Differential ScanningCalorimeter) analysis indicate that the Al-P modifier has more advantages over Cu-P and Fe-Pmodifier in easily addition, no elemental alteration and less undercooling of primary silicon'ssolidification, which suggests the Al-P master alloy is an effective modifier of eutectic Al-Sialloys.

Evolution of V-containing phases during preparation of Al-based Al−V master alloys

Al-based Al−V master alloys were prepared by both the stepwise heating melting experiment and stepwise melting cooling experiment with rapid solidification to investigate the transformation of V-containing phases which gave different effects on microstructures and properties of commercial Al alloys and Ti alloys,as both melting and solidification processes affect the evolution of V-containing phases largely.The results showed that the raw Al−50wt.%V alloy consisted of needle-like Al_(3)V phase and Al8V5 phase(matrix),while petal-like Al_(3)V,needle-like Al_(7)V and plate-like Al_(10)V phase were present in the Al−V master alloys.The metastable Al_(7)V phase was evolved from Al_(3)V phase and then evolved into Al_(10)V phase during melting process.The number of Al_(10)V phase increased with the decrease of temperature in the range of 800−1000℃.Petal-like Al_(3)V phases could be transformed from Al_(8)V_(5) phase,pre-precipitated from Al−V molten liquid during melting process and precipitated directly during rapid solidification,respectively.

Effects of Al-10Sr master alloys on grain refinement of AZ31 magnesium alloy

The effects of Al-10Sr master alloys on grain refinement of AZ31 magnesium alloy were investigated,and the refinement efficiency of different Al-10Sr master alloys(commercial,solubilized,rolled and remelted+rapidly cooled)was compared and analyzed.The results indicate that the morphology and size of Al4Sr phases in the microstructures of different Al-10Sr master alloys,are of great difference.For the commercial Al-10Sr master alloy,the Al4Sr phases evolve from coarse block shape to relatively fine block shape after being dissolved at 500 ℃ for 4 h and followed by water quenching;but after being rolled at 300 ℃ for 50% reduction or remelted and followed by rapid cooling,the Al4Sr phases mainly exhibit fine granule and fibre shapes.In addition,the different Al-10Sr master alloys can effectively reduce the grain size of AZ31 magnesium alloy,but their refinement efficiency is different.The refinement efficiency of the Al-10Sr master alloy obtained by remelting and rapid cooling is the best,then the rolled,solubilized and commercial Al-10Sr master alloys are in turn.The difference of refinement efficiency for different Al-10Sr master alloys may be related to the dissolution rates of Al4Sr phases with different morphologies and sizes in the melt of AZ31 magnesium alloy.

Grain reinement limit of commercial pure Al inoculated by Al-Ti-C(B) master alloys

The grain reifnement limits of commercial pure Al inoculated by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master al oys were studied, and the inlfuence of melting temperature on the grain reifning performance of these three master al oys was investigated using a high scope video microscope （HSVM）, a ifeld-emission scanning electron microscope （FESEM）, an electron probe micro-analyzer （EPMA） and X-ray diffraction （XRD） method. Results show that there is a grain reifnement limit of commercial pure Al reifned by these three master al oys; with the same addition level of 1.5% under the present experimental conditions, the grain reifnement limits （smal est average grain size） of commercial pure Al reifned by Al-5Ti-1B, Al-5Ti-0.25C and Al-5Ti-0.3C-0.2B master al oys are 50 μm, 80 μm and 80 μm, respectively. In addition, with an increase in the melting temperature of the pure Al, the grain reifning performance of Al-5Ti-1B and Al-5Ti-0.25C master al oys decreases, but the grain reifning performance of Al-5Ti-0.3C-0.2B changes little.

United modification of Al-24Si alloy by Al-P and Al-Ti-C master alloys

The modification effect of a new type of Al-P master alloy on Al-24Si alloys was investigated. It is found that excellent modification effect can be obtained by the addition of this new type of Al-P master alloy into Al-24Si melt and the average primary Si grain size is decreased below 47 μm from original 225 μm. It is also found that the TiC particles in the melt coming from Al8Ti2C can improve the modification effect of the Al-P master alloy. When the content of TiC particles in the Al-24Si melt is 0.03%, the improvement reaches the maximum and keeps steady with increasing content of TiC particles. Modification effect occurs at 50 min after the addition of the Al-P master alloy and TiC particles, and keeps stable with prolonging holding time.

Grain refinement of AZ31 magnesium alloy by new Al-Ti-C master alloys

New Al4C3-containing Al-Ti-C master alloys (Al-0.6Ti-1C and Al-1Ti-1C) were developed by introducing Ti element into Al-C melt using melt reaction method,in which most of the TiC particles distribute around Al4C3 particles. It is believed that most of the C firstly reacts with Al melt and form Al4C3 particles by the reaction Al(l)+C(s)→Al4C3(s),and after adding Ti into the Al-C melt,the size of Al4C3 particles is decreased and the distribution of Al4C3 is improved through the reaction Ti(solute)+Al4C3(s)→ TiC(s)+Al(l). With the addition of 1% Al-1Ti-1C master alloy,the average grain size of AZ31 is reduced sharply from 850 μm to 200 μm,and the grain morphology of α-Mg transits from a fully-developed equiaxed dendritic structure to a petal-like shape. Al-C-O-Mn-Fe compounds are proposed to be potent nucleating substrates for primary Mg. Appropriate addition of Ti is believed to increase the grain refinement efficiency of Al4C3-containing Al-Ti-C master alloys in AZ31 alloy.

Effects of various Mg-Sr master alloys on microstructural refinement of ZK60 magnesium alloy

The effects of various Mg-Sr master alloys(conventional as-cast,rapidly-solidified,rolled and solutionized) on microstructural refinement of ZK60 magnesium alloy were investigated.The results indicate that the refinement efficiency of various Mg-Sr master alloys in ZK60 alloy is different.The rolled Mg-Srmaster alloy is found to have relatively higher refinement efficiency than the conventional as-cast,solutionized and rapidly-solidified Mg-Sr master alloys.After being treated with the rolled Mg-Sr master alloy,the ZK60 alloy obtains the minimum average grain size of 33μm.The difference of various Mg-Sr master alloys in refinement efficiency might be related to the initial microstructure change of various Mg-Sr master alloys.

Structural heredity between Al5Ti1B and AlTi, AlB master alloys

Al5Ti1B master alloy was produced by two-step method. Experimental results show that the structure of Al5TilB master alloy depends on that of AlTi and AlB master alloys, the morphologies of TiAl3 depend on AlTi master alloy and the boride phases depend on AlB master alloy. There are remarkable structure heredity between Al5Ti1B master alloy and AlTi, AlB master alloys. Theoretical analyses show that AlTi and Al-B master alloys can change the melt structure of Al5Ti1B master alloy, then affect the solid structure of the master alloy.