Grain refinement of Al-3.5FeNb-1.5C master alloy on pure Al and Al-9.8Si-3.4Cu alloy

The refinement potential of Al-3.5 Fe Nb-1.5 C master alloy on pure aluminium and Al-9.8 Si-3.4 Cu alloy has been investigated. Different amounts of Al-3.5 Fe Nb-1.5 C master alloy were added to estimate the optimal addition level. It was found that the addition of Al-3.5 Fe Nb-1.5 C grain refiner can promote significantly the refinement of grains in the pure aluminium, particularly at 0.1 wt.%, with the mean primary aluminium α-grain size reducing to 187±3 μm from about 1-3 mm. Similarly, the microstructural study of the Al-9.8 Si-3.4 Cu alloy die casting at different weight percentages(viz. 0.0 wt.%, 0.1 wt.% and 1.0 wt.%) of Al-3.5 Fe Nb-1.5 C master alloy shows that the Al-3.5 Fe Nb-1.5 C master alloy as a grain refiner is also acceptable for Al-Si cast alloys when the silicon content is more than 4 wt.%. As a result of inoculation with Al-3.5 Fe Nb-1.5 C master alloy, the average grain size of α-Al is reduced to 22±3 μm from about 71±3 μm and grain refining efficiency is not characterized by any visible poisoning effect, which is the major limitation in the grain refinement of Al-Si cast alloys by applying Al-Ti-B ternary master alloys. Mechanical properties such as ultimate tensile strength and yield strength are significantly improved by 9.6% and 9.7%, respectively.     

Study of Melt Thermal-Rate Treatment and Low-Temperature Pouring on Al-15%Si Alloy

Under the condition of melt thermal-rate treatment (MTRT) and low-temperature pouring (LTP), the tensile properties of Al-15%Si alloy are improved, the average size of primary Si is refined to about 20 μm from about 50 μm, and eutectic silicon can be well modified. The ultimate tensile strength and elongation are 201 MPa and 3.5%, and these values increase by 12% and 25%, respectively, compared with that obtained by conventional casting technique. The Al-15%Si alloy modified with Sr and RE additions was also studied for comparison purposes. The tensile properties of the Al-15%Si alloy treated with MTRT + LTP are superior to those modified with Sr or RE addition individually. The eutectic growth temperature difference between modified and unmodified melts was used to indicate the modification level. The modification effect of MTRT + LTP on Al-15%Si alloy is better than that modified with Sr or RE addition.     

Intensive melt shearing and calcium concentration effects on grain refinement of commercial purity Mg

The effects of intensive melt shearing and Ca concentration on grain refinement of commercial purity Mg have been investigated by standard TP-1 casting tests, X-ray diffraction combined with the observation of optical microscope and scanning electron microscope. It was found that, without intensive melt shearing, Ca addition greatly improved grain structure of Mg from columnar grain to equiaxed grain. With Ca concentration increasing from 0.01 to 1 wt. %, the average grain size of the alloy gradually decreased. When intensive melt shearing was applied, the grain structures of the alloy remained equiaxed grain with Ca concentration variation. The average grain size first decreased and then kept invariable with Ca concentration increasing to 1 wt. %. The grain refining mechanism of Ca concentration variable and intensive melt shearing was discussed.     

Regarding the processing associated microstructure and mechanical properties improvement of an Al-4.5 Cu alloy

In the present study, an Al-4.5 wt. % Cu alloy was synthesized using a casting technique and a new disintegrated melt deposition technique. Microstructural characterization studies conducted on the samples taken from disintegrated melt deposition technique revealed a relatively more equiaxed grain morphology when compared to the cast samples. Microporosity, which is unavoidable for the columnar-equiaxed matrix microstructure was found to be less in case of disintegrated melt deposited samples when compared to the cast samples. Results of ambient temperature mechanical tests demonstrate that disintegrated melt deposited samples exhibited similar 0.2% yield stress, 1.52 times ultimate tensile strength and 3.69 times ductility when compared to the cast samples. All attempt is made to correlate the results of microstructural characterization and mechanical testing with the nature of processing technique employed to synthesize Al-4.5 wt. % Cu alloy.     

Determination of Coherency and Rigidity Temperatures in Al-Cu Alloys Using In Situ Neutron Diffraction During Casting

The rigidity temperature of a solidifying alloy is the temperature at which the solid phase is sufficiently coalesced to transmit tensile stress. It is a major input parameter in numerical modeling of solidification processes as it defines the point at which thermally induced deformations start to generate internal stresses in a casting. This temperature has been determined for an Al-13 wt.% Cu alloy using in situ neutron diffraction during casting in a dog-bone-shaped mold. This setup allows the sample to build up internal stress naturally as its contraction is not possible. The cooling on both sides of the mold induces a hot spot at the middle of the sample that is irradiated by neutrons. Diffraction patterns are recorded every 11 s using a large detector, and the very first change of diffraction angles allows for the determination of the rigidity temperature. We measured rigidity temperatures equal to 557°C and 548°C depending on the cooling rate for grain refined Al-13 wt.% Cu alloys. At a high cooling rate, rigidity is reached during the formation of the eutectic phase. In this case, the solid phase is not sufficiently coalesced to sustain tensile load and thus cannot avoid hot tear formation.     

Effects of Cu Content on Thermal Stability and Wear Behavior of Al-12.5Si-1.0Mg Alloy

This study investigates how Cu content affects thermal stability and wear behavior of Al-12.5Si-1.0Mg alloy, by adding 2.55 and 4.53 wt.% Cu. The low-Cu and high-Cu alloys were isothermally heat-treated at 300 °C for 100 h. The results indicated that the amount of eutectic Al₂Cu and Al₅Cu₂Mg₈Si₆ particles in the high-Cu alloy was more than that in the low-Cu alloy. These hard particles retained in the Al matrices during isothermal heat treatment, maintaining a relatively stable hardness. Therefore, the hardness of the high-Cu alloy was superior to that of the low-Cu alloy in as-cast condition and after isothermal heat treatment. For wear behavior, both isothermal heat-treated alloys showed the same wear rate with 10 N normal load. The wear rate of Al-12.5Si-1.0Mg alloy was independent on the copper content under 10 N load, but the wear rate at a load of 40 N decreased with increasing Cu content in Al-12.5Si-1.0Mg alloy.     

Effect of Heat Treatment on the Properties of AlCu26Si8

ABSTRACT

In this paper, in situ centrifugal casting was proposed to fabricate Al-26 wt.% Cu-7.8 wt.% Si FG pipe with the density of 3.5 g/cm³ and also the wear resistance of 0.0241g/mm². The casting mould is preheated to approximately 200°C to avoid chilling effects, segregation, porosity and compensation of the shrinkage of the alloy during the casting. The microstructure results show that the Al₂Cu content smoothly decreases from the outer layer to inner layer. Vickers hardness, coefficient of thermal expansion (CTE) and mechanical properties of the present FG pipe are measured to show the significant dependence of the microstructure. Furthermore, the heat treatment of the samples are conducted in boiling water (100°C) for 4.5 h to promote the formations of new Al₂Cu particles into the α–Al phase and consequently improve the hardness and CTE of the FG pipe.     

Processing Effects on Grain Refinement of AZ31 Magnesium Alloy Treated with a Commercial Al-10Sr Master Alloy

The effects of Sr amount and melt holding time on the grain refinement of AZ31 magnesium alloy treated with a commercial Al-10Sr master alloy are investigated. The effects of solutionizing, rolling, and remelting of commercial Al-10Sr master alloy on the grain refinement of AZ31 magnesium alloy are also investigated. An increase in Sr amount from 0.01 to 0.1 wt.% or melt holding time from 20 to 80 min causes the grain size of AZ31 alloy treated with the commercial Al-10Sr master alloy to gradually decrease. In addition, the solutionizing, rolling, or remelting of commercial Al-10Sr master alloy can improve the refinement efficiency of the master alloy to AZ31 alloy, and the improvement resulting from the remelting is best obvious, followed by rolling and solutionizing, respectively.     

Grain Refiner Effect on the Microstructure and Mechanical Properties of the A356 Automotive Wheels

A356 aluminum alloy automotive wheels, 17 inch in diameter, were produced by low-pressure die casting. Contents of Al-5Ti-B (ATB) master alloy were added from 0 to 0.79 wt.%. Microstructural and mechanical properties were evaluated under industrial casting process conditions. The obtained results from mechanical testing provide evidence that additions of 0.13 and 0.27 wt.% of ATB have an improvement on the mechanical performance of the automotive wheels. This can be compared with the use of a grain refiner’s higher concentrations, leading to a significant reduction in the cost-benefit ratio for the manufacturing of A356 automotive wheels.     

Fluidity,Microstructure, and Tensile Properties of Sub-rapidly Solidified Mg-6Al-4Zn-xSn(x=0,0.6,1.2,1.8) Alloy

In this paper, the infl uence of the Sn element on the melt viscosity, grain size, shrinkage, and tensile properties of the subrapidly solidified Mg-6Al-4Zn alloy was studied. The results showed that the melt viscosity of the Mg-6Al-4Zn alloy was greatly decreased because of the addition of Sn. As the content of Sn increased from 0 to 1.8 wt.%, the grain size of the alloy was refined, and the dendrite microstructure was changed to rose-shaped ones simultaneously. The decreased melt viscosity and refined microstructure were conductive to the feeding of melt, which contributed to the reduction in volume fraction of shrinkage. The volume fraction of shrinkage of the Mg-6Al-4Zn-1.2 Sn alloy was reduced by 30.8%, compared with that of the alloy without Sn addition. Tensile properties of the Mg-6Al-4Zn-x Sn alloys were increased firstly and then decreased with the augmented Sn content. The yield strength, ultimate tensile strength, and elongation of the alloy containing 1.2 wt.% Sn were 21.4%, 39.5%, and 259.0% higher than those of the alloy without Sn addition, respectively. The addition of Sn was considered to reduce the shrinkage of the sub-rapidly solidified Mg-6Al-4Zn magnesium alloy and thus improved its tensile properties. To identify the mechanism, the effect of Sn on the volume fraction of shrinkage was discussed from three aspects of melt viscosity, grain refinement, and volume fraction of eutectic phases.     

Effect of Hypoeutectic Boron Additions on the Grain Size and Mechanical Properties of Ti-6Al-4V Manufactured with Powder Bed Electron Beam Additive Manufacturing

In additive manufacturing, microstructural control is feasible via processing parameter alteration. However, the window for parameter variation for certain materials, such as Ti-6Al-4V, is limited, and alternative methods must be employed to customize microstructures. Grain refinement and homogenization in cast titanium alloys has been demonstrated through the addition of hypoeutectic concentrations of boron. This work explores the influence of 0.00 wt.%, 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% boron additions on the microstructure and bulk mechanical properties of Ti-6Al-4V samples fabricated in an Arcam A2 electron beam melting (EBM) system with commercial processing parameters for Ti-6Al-4V. Analyses of EBM fabricated Ti-6Al-4V + B indicate that the addition of 0.25–1.0 wt.% boron progressively refines the grain structure, and it improves hardness and elastic modulus. Despite a reduction in size, the β grain structure remained columnar as a result of directional heat transfer during EBM fabrication.     

等通道转角挤压Al-Cu合金的冲击性能

对铸态Al-0.63%Cu和Al-3.9%Cu(质量分数)合金进行等通道转角挤压处理,研究了Al-Cu合金冲击性能的变化.结果表明,等通道转角挤压增强了Al-0.63%Cu合金的冲击性能;而对于Al-3.9%Cu合金,虽然晶粒细化和第二相的弥散分布使其强度增加,但较多的第二相θ(Al2Cu)未提高其冲击性能.该合金的冲击吸收功与其静力韧度有关.     

Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt

It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites.     

Effect of Homogenization Temperature on Microstructure and Conductivity of Al-Mg-Si-Ce Alloy

Microstructure evolution of Al-0.2wt.%Mg-0.36wt.%Si-0.3wt.%Ce alloy at three different homogenization temperatures for 6 h was observed by optical microscopy, scanning electron microscopy, and x-ray diffraction. Conductivity and tensile properties of the alloy were tested. Results indicate that homogenization temperature has little effect on the macro-segregation and grain size of the as-cast Al-Mg-Si-Ce alloy; however, it has a significant effect on the conductivity. The conductivity is first improved to a maximum value of about 57.3% IACS with homogenization temperature increasing to 560 °C (2.7% higher than that of the as-cast sample), and then decreased when the temperature continuously increasing. The main contributor is considered to be vacancy concentration, which is directly related to the lattice distortion, thus affects the conductivity. The studied homogenization temperatures almost make no difference among the tensile properties of the alloy. The best homogenization temperature for Al-0.2wt.%Mg-0.36wt.%Si-0.3wt.%Ce alloy is 560 °C with the highest conductivity and no decrement of strength.     

Ce和Sb及时效处理对Mg-Zn-Al系铸造镁合金组织的影响

利用SEM、X射线衍射等手段研究了微量元素Ce和Sb及时效处理对Mg-Al-Zn系铸造合金组织和性能的影响。结果表明:Ce和Sb元素显著地细化了试验合金铸态组织,改善β相形貌及分布,并形成呈粒状弥散分布Mg3Sb2、Al11Ce3、CeCu6的新相;Mg-10Zn-2Al-1Cu+0.5%(Ce+Sb)试验合金的时效沉淀过程中弥散析出粒状、杆状析出相(Mg32(Al,Zn)49、Mg32Al47Cu7、Mg3Zn2、Mg3Sb2、CeCu6等),且其析出相的形成、析出速度和长大速度等都远远小于AZ91D合金,显示较好的时效强化效应。     

Brazing of 6061 aluminum alloy/Ti-6Al-4V using Al-Si-Cu-Ge filler metals

Al-8.4Si-20Cu-10Ge and mixed rare-earth elements (Re) containing Al-8.4Si-20Cu-10Ge-0.1Re filler metals were used for brazing of 6061 aluminum alloy/Ti-6Al-4V. The addition of 20 wt.% copper and 10 wt.% germanium into the Al-12Si filler metal lowered the solidus temperature from 586 °C to 489 °C and the liquidus temperature from 592 °C to 513 °C. The addition of 0.1 wt.% rare-earth elements into Al-8.4Si-20Cu-10Ge alloy caused remarkable Al-rich phase refinement and transformed the needle-like Al₂Cu intermetallic compounds into block-like shapes. Shear strengths of the 6061 aluminum alloy/Ti-6Al-4V joints with the two brazing filler metals, Al-8.4Si-20Cu-10Ge and Al-8.4Si-20Cu-10Ge-0.1Re, varied insignificantly with brazing periods of 10-60 min. The average shear strength of the 6061 aluminum alloy/Ti-6Al-4V joints brazed with Al-8.4Si-20Cu-10Ge at 530 °C was about 20 MPa. Rare-earth elements appeared to improve the reaction of the Al-8.4Si-20Cu-10Ge filler metal with Ti-6Al-4V. The joint shear strength of the 6061 aluminum alloy/Ti-6Al-4V with Al-8.4Si-20Cu-10Ge-0.1Re reached about 51 MPa.     

Influence of melt hydrogenation during induction skull melting process on the solidification microstructure of Ti-6Al-4V alloy

A new method to modify the solidification microstructure of titanium alloys, named melt hydrogenation, by adding TiH2 as additive into the melt of titanium alloys during induction skull melting process (ISM), is put forward and the refining effect of this method on the solidification microstructure of Ti-6Al-4V alloy was studied experimentally. After melt hydrogenation, the grain sizes of as-cast Ti-6Al-4V alloy decreased to 612 μm from 1,072 μm, lath-shaped α phase was also refined and fine α/β lamellar microstructure was formed when 1.0 wt.% TiH2 was added. δ-hydride was found in the X-ray diffraction (XRD) spectra of Ti-6Al-4V alloy that prepared with 1.0 wt.% TiH2 added and the δ-hydride distributes in α phase as acicular precipitations.     

Influence of Cu Addition on the Structure,Mechanical and Corrosion Properties of Cast Mg-2%Zn Alloy

Effects of different concentrations of Cu on the structure, mechanical and corrosion properties of Mg-2%Zn alloy were studied by the use of x-ray diffraction, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, standard tensile testing, polarization and electrochemical impedance spectroscopy (EIS) measurements. The average grain size of the alloy decreased from above 1000 μm to about 200 μm with 5 wt.% Cu addition in as-cast condition. Microstructural studies revealed that Mg-2Zn-xCu alloys matrix typically consists of primary α-Mg and MgZnCu and Mg(Zn,Cu)₂ intermetallics which are mainly found at the grain boundaries. The results obtained from mechanical testing ascertained that Cu addition increased the hardness values significantly. Although the addition of 0.5 wt.% Cu improved the ultimate tensile strength and elongation values, more Cu addition (i.e., 5 wt.%) weakened the tensile properties of the alloy by introducing semi-continuous network of brittle intermetallic phases. Based on polarization test results, it can be concluded that Cu eliminates a protective film on Mg-2%Zn alloy surface. Among Mg-2%Zn-x%Cu alloys, the one containing 0.1 wt.% Cu exhibited the best anti-corrosion property. However, further Cu addition increased the volume fraction of intermetallics culminating in corrosion rate enhancement due to the galvanic couple effect. EIS and microstructural analysis also confirmed the polarization results.     

Tensile properties and fracture characteristics of ECAP-processed Al and Al-Cu alloys

In the present paper, billets of pure Al, and cast-homogenized Al-2 wt.%, 3 wt.%, and 5 wt.% Cu alloys were successfully processed by equal channel angular pressing (ECAP) up to 10 passes without fracture at room temperature using a die with a channel angle of 110°. Giant strains imposed on workpieces lead to extreme dislocation densities, microstructural refinement, and finally ultrafine grained materials. Tensile tests were employed to examine the fracture modes and fracture surface morphologies of the ECAP-processed Al and Al-Cu alloy samples. In particular, the effects of the number of ECAP passes and the Cu content were investigated.