Al-B Master Alloys Research Articles

On the Role of Al-B Master Alloy and Heat Treatment on Synergistic Improvement in Electrical Conductivity and Hardness of Al-Mg-Si Alloys

On the Role of Al-B Master Alloy and Heat Treatment on Synergistic Improvement in Electrical Conductivity and Hardness of Al-Mg-Si Alloys

On the grain refining efficacy of Ti-free hypoeutectic AlSi via AlTiB, AlB and AlNbB chemical inoculation

Metals with a fine grain structure have intrinsic advantages like higher mechanical strength and more isotropic behaviour. An effective way of refining the grain size is via chemical inoculation. In this study the grain refining efficacy of AlTiB, AlB and AlNbB master alloys on a Ti-free AlSi alloy is investigated. In particular, the performance of commercial Al5Ti1B and Al5B master alloys is compared to that of a lab-made Al2Nb2B and two Al2NbxB (x = 1 and 2 wt%) made in an industrial pilot scale facility. Although chemical inoculation does not change the morphology of the grains, which is always equiaxed dendritic, it is found that the grain size progressively decreases with the master alloy addition rate and the achievable final grain size is strongly dependent on the chemistry of the master alloy used. The experimental results demonstrate that AlNbB > AlB > AlTiB in terms of grain refining efficacy.

The grain refinement of 1070 alloy by different Al-Ti-B mater alloys and its influence on the electrical conductivity

The excellent grain refinement effectiveness and good electrical conductivity is difficult to be simultaneously obtained due to the influence of both the grain boundary and excessive Ti in the usually used refiners, such as Al-5Ti-1B master alloy. In order to solve this problem, in this work, Al-Ti-B mater alloys with less or without excessive Ti but with high refinement potency TiB2 have been tried to prepare, and the grain refinement effectiveness of them and its influence on the electrical conductivity of the refined Al have been investigated. It is found that the grain refinement effectiveness of the Al-Ti-B master alloys prepared using the Al-5Ti-1B and Al-B master alloys as the starting materials at 720 °C is much better than those prepared using the Al-10Ti and Al-B master alloys, which is because that the high refinement potency TiB2 with TiAl3 2DC in the Al-5Ti-B can be kept in the prepared master alloys. As a result, using the prepared Al-Ti-B master alloys as the refiners, both the good grain refinement effectiveness and improved electrical conductivity of Al can be realized.

Boride phase formation in the production of Al-B master alloys

The formation of boride phases is studied in the production of Al-B master alloys, which involves chemical reactions of KBF4 and aluminum melts. Boron is reduced from KBF4 and reacts with aluminum to form AlB12 and AlB2 depending on processing conditions. AlB12 forms at the Al/flux interface and subsequently reacts with aluminum to form AlB2 in a slow process while moving away from the Al/flux interface. In designed experiments, aluminum reacted with KBF4 droplets producing dense AlB12 shells trapping KAlF4 salt inside at high temperatures. In comparison, the majority of individual AlB2 particles is located near the Al/flux interface inside the aluminum matrix in a circular shape. Meanwhile, a uniform dispersion of AlB2 particles in the aluminum matrix is also observed away from the Al/flux interface. It is revealed that boron, after being reduced from KBF4 by aluminum, has a high tendency to build up at the Al/flux interface, forming AlB12 and subsequently transforming to AlB2.

Preparation of silicon target material by adding Al-B master alloy in directional solidification

The silicon target material was prepared by adding Al-6B master alloy in directional solidification. The microstructure was characterized and the resistivity was studied in this work. The results showed that the purity of the silicon target material was more than 99.999% (5N). The resistivity was ranges from 0.002 to 0.030 Ω·cm along the ingot height. It was revealed that the particles of AlB2 in Al-6B master alloy would react spontaneously and generate clusters of [B] and [Al] in molten silicon at 1723 K. After directional solidification, the content of B and Al were increasing gradually with the increase of solidified fraction. The measured values of B were in good agreement with the curve of the Scheil equation below 80% of the ingot height. The mean concentration of B was about 17.20 ppmw and the mean concentration of Al was about 8.07 ppmw after directional solidification. The measured values of Al were fitting well with the curve of values which the effective segregation coefficient was 0.00378. It was observed that B co-doped Al in directional solidification polysilicon could regulate resistivity mutually. This work provides the theoretical basis and technical support for industrial production of the silicon target material.

Grain Refinement of High-Iron Aluminum Alloy by Inoculation with Al-B Master Alloy

Aluminum cables are playing an increasingly important role in power transmission system, in which the “rare-earth high-iron aluminum alloy power cables were developed in China. In this paper, the effects of B on grain refinement of high-iron aluminum alloy were studied by using OM (optical microscopy), SEM (scanning electron microscopy), EDX (energy dispersive X-Ray spectroscopy) and XRD (X-ray diffraction). And the conductivity of high-iron aluminum alloy was also tested. The results showed that B could take significant effects on grain refinement and promote the increase of conductivity. The refinement may be mainly due to the eutectic reaction in solidification process and the formation of AlB2 particles. The optimal concentration of B was determined as 0.06 wt. %.

Modification of aluminium and aluminium alloys by AL-B master alloy

Chemical compositions and microstructures affect on mechanical – physical and working properties of aluminium and aluminum alloys. Transition elements, such as Ti, V, Cr, Zr in solid solution greatly reduce the electrical conductivity of aluminium and its alloys. For reduction of detrimental effects of transition elements, Al-B master alloys are added into molten aluminium to occur reactions of boron and transition elements to form diborides of titanium, vanadium, chromium and zirconium, which are markedly insoluble in molten aluminium, then these transition elements have an insignificant effects on conductivity. In addition, Al-B master alloys is also used as a grain refiner of aluminium and aluminium alloys. Aluminium borides particles in Al-B master alloys act as substrates for heterogeneous nucleation of aluminium and its alloys. Al-B master alloys are prepared from low cost materials, such as boric acid H3BO3 and cryolite Na3AlF6, by simple melting method, easily realize in electrical wire and cable factories.

Removal of Vanadium from Molten Aluminum—Part III. Analysis of Industrial Boron Treatment Practice

Transition metal impurities (V, Ti, Zr, and Cr) reduce the electrical conductivity of smelter grade aluminum. These impurities are removed in the form of their borides by reacting with added Al-B master alloys i.e., boron treatment. Although, boron treatment is widely used for the production of high purity aluminum alloys in casthouse the fundamental understanding is lacking and published industrial data are limited. In the current study, industrial trials on the removal of impurities were conducted at one of the high purity aluminum alloys producers in Australasia. Kinetics analysis revealed that the rate of reaction is controlled by the mass transfer of impurities in the bulk melt. The measured mass transfer coefficient (k m) of V and Ti were 1.1 × 10−4 and 2.6 × 10−4 m/s respectively, in the naturally stirred molten aluminum. The rate of V and Ti removal was faster compared to Zr and Cr during the boron treatment of smelter grade aluminum. Mass balance analysis revealed that 70 wt pct of V and Ti combined as borides in the first hour of the total 12 hours of boron treatment process. The calculated amount of un-reacted B was approximately 25.5 wt pct of initial amount added that remained in the final alloy. There was no evidence of boride rings formation, although partially dissolved AlB12 particles were observed under scanning electron microscope. Finally, implications for industrial practice are discussed for the improvement of current boron treatment process that include changing the source of boron, multiple stage addition of boron and better stirring of the molten aluminum.

Removal of Vanadium from Molten Aluminum-Part I. Analysis of VB2 Formation

Aluminum has been used as an alternative to copper for electrical conductor applications. However, the presence of certain impurities in aluminum, such as V, Ti, Zr, Cr, and Fe, has detrimental effect on its electrical conductivity. These impurities can be removed by the addition of an Al-B master alloy containing AlB2 or AlB12 phase, known as boron treatment. The detailed mechanism of borides formation, however, is not well understood. In the current study, a systematic investigation of vanadium diborides (VB2) formation in the Al-V-B alloys was carried out. The study comprised thermodynamic assessment and experimental investigation on the Al-V-B system under typical industrial processing conditions. It was predicted from thermodynamic analysis that VB2 are stable borides of V and do not dissolve readily in the temperatures ranging from 948 K to 1173 K (675 °C to 900 °C). The experimental investigation showed that the mechanism of VB2 formation and V removal in an Al-V-B system is complex as it involves a number of steps such as chemical reaction, mass transfers in bulk liquid and inside the VB2 ring, and diffusions of B and V through the VB2 layer. Comparative analysis of thermodynamic and experimental results showed that the aluminum alloys were far from equilibrium and that the overall process was limited by the kinetics of B diffusion through the VB2 ring.

Grain refining performance of Al-B master alloys with different microstructures on Al-7Si alloy

The improved halide salt route has been employed to produce Al-3B master alloys with different microstructures. The micro-structural features of AlB2 particles exhibited different impacts on the grain refining response of Al-7Si alloy, evolving with the holding time after inoculation. Large blocky AlB2 particles suffer from an intense fading effect while strip-like particles are not effective enough at the 0.005 wt% B addition level. Among the various Al-3B master alloys, sample 1 containing fine, blocky AlB2 particles was revealed to be the most efficient in refining Al-7Si alloy. With inoculation of only 0.005%B of such alloy, the final grain size of Al-7Si alloy can reach 238 μm. Its grain refining efficiency was more or less retained for holding times up to 60 min.

Response to Thermal Exposure of Ball-Milled Aluminum-Borax Powder Blends

Aluminum-borax powder mixtures were ball milled and heated above 873 K (600 °C) to produce Al-B master alloys. Ball-milled powder blends reveal interpenetrating layers of deformed aluminum and borax grains that are increasingly refined with increasing milling time. Thermal exposure of the ball-milled powder blends facilitates a series of thermite reactions between these layers. Borax, dehydrated during heating, is reduced by Al, and B thus generated reacts with excess Al to produce AlB2 particles dispersed across the aluminum grains starting at 873 K (600 °C). AlB2 particles start to form along the interface of the aluminum and borax layers. Once nucleated, these particles grow readily to become hexagonal-shaped crystals that traverse the aluminum grains with increasing temperatures as evidenced by the increase in the size as well as in the number of the AlB2 particles. Ball milling for 1 hour suffices to achieve a thermite reaction between borax and aluminum. Ball milling further does not impact the response of the powder blend to thermal exposure. The nucleation-reaction sites are multiplied, however, with increasing milling time and thus insure a higher number of smaller AlB2 particles. The size of the AlB2 platelets may be adjusted with the ball milling time.

Effect of B/Ti mass ratio on grain refining of low-titanium aluminum produced by electrolysis

The effect of B/Ti mass ratio on grain refining of the low-titanium aluminum produced by electrolysis was investigated by adding AlB master alloy to the melt of the low-titanium aluminum. The results show that the addition of titanium by electrolysis is an effective way of grain refining of aluminum, and addition of boron to the melt of the low-titanium aluminum can further increase the grain refining efficiency. And the best grain refining efficiency is obtained when the B/Ti mass ratio is 1:10. However, when the B/Ti mass ratio is 1:2.22 (the stoichiometric value for TiB 2), the grain refining efficiency vanishes almost completely. It means that all of the solute titanium atoms in the melt of the low-titanium aluminum react with boron atoms that come from AlB master alloy to form TiB 2 particles, and TiB 2 particles have not grain refining ability. The grain refining efficiency seems to increase with addition of more boron to the melt after the B/Ti mass ratio exceeds 1:2.22. But the grain refining efficiency is very poor, and similar to that of pure Al refined by AlB master alloy. It further shows that TiB 2 particles do not participate in grain refining, and that the excess boron atoms in the melt also cannot turn TiB 2 particles into the effective nuclei for aluminum as the solute titanium atoms do.

Grain Refinement of Cast Al Alloys by Al-B Master Alloy

The effects of boron on the grain refinement of Al alloys are investigated. Small addition of boron has no effects on the grain refinement of pure aluminum and Si free Al alloys. These alloys are, however, well grain-refined with low Si content of 0.1∼0.5mass%. The binary hypoeutectic Al-Si alloys are also refined by boron addition independently on the Si concentration. The grain refining effects are kept after long holding times, high holding temperature on the melt conditions and remelting. The boride particles in the Al-B master alloy do not act as effective nuclei of α -Al and it is doubtful whether the heterogeneous nucleation of a -Al occurs directly on AlB 2 . The grain refinement mechanism should be focused on the reactions of Al-Si-B ternary system.

Effect of Al-Ti and Al-B master alloy addition on the grain refinement of stationary arc-melted Al weld

Effect of Al-Ti and Al-B master alloy addition on the grain refinement of stationary arc-melted Al weld