Na-Ba复合变质对改良铸造铝-硅合金组织和性能的影响

以ZL101铝合金为基础,通过添加Cu、Ni、Mn、V、RE等合金元素,研制了改良铸造铝-硅合金,并研究了Na-Ba复合变质对该合金组织和性能的影响。结果表明,Na-Ba复合变质对改良铸造铝-硅合金是有效的,而且变质处理没有潜伏期,持续时间长,变质效果好。     

新型变质剂Pr_2(CO_3)_3对ZL107的变质作用及性能影响

利用金相显微镜和磨擦磨损试验机研究了新型稀土变质剂Pr2(CO3)3盐在不同含量、保温时间以及浇铸温度等条件下对ZL107铝合金变质作用。研究结果表明:稀土Pr2(CO3)3盐含量为3.0%时其变质效果最佳;浇铸温度对其变质效果影响不大;Pr2(CO3)3具有较长的变质失效时间。此外,还对比分析了变质前后合金的耐磨性能。     

Dry Sliding Wear Properties of AZ31-Mg<Subscript>2</Subscript>Si Magnesium Matrix Composites

AZ31-Mg₂Si in situ composites were prepared from AZ31 Mg alloy and Si particles by a gravity casting method. Several parameters, such as Si content, normal load, and environmental temperature, were varied in order to study their effects on the composite dry sliding wear properties. Tensile properties and hardness of the composites were also investigated. The obtained results showed that the wear resistance, yield strength, and hardness of the AZ31-Mg₂Si composites increased with size and quantity of the Mg₂Si phase. However, when the environmental temperature increased from 25 to 190 °C, the composite wear resistance and ultimate tensile strength gradually decreased due to softening of the AZ31 matrix.     

High Wear-Resistant Aluminum Matrix Composite Layer Fabricated by MIG Welding with Lateral B<Subscript>4</Subscript>C Powder Injection

In this work, a low-cost technique combining MIG welding and lateral powder injection was developed to fabricate B₄C particles-reinforced aluminum matrix composite (AMC) layer on a T6 heat-treated 7075 aluminum alloy (AA7075-T6) substrate. The AMC layer was 6-7 mm thick and well bonded to the substrate. The B₄C particles were dispersed throughout the AMC layer with an average content of approximately 7 vol.%. No significant reaction products existed either at the particle–matrix interface or in the Al-matrix. In pin-on-disk dry sliding wear tests against Al₂O₃ grinding wheels, the AMC layer exhibited excellent wear resistance with volume wear rate approximately 1/10-3/10 that of the quenched AISI 1045 steel and only approximately 2-7% that of the AA7075-T6 alloy under the same wear conditions. A small addition of ceramic particles can greatly improve wear resistance, suggesting that this technique has good prospects for a wide variety of applications.     

Experimental and theoretical investigation of stress variation in AlCu<Subscript>4</Subscript>Mg<Subscript>1</Subscript> aluminum alloy

This paper presents the results of experimental and theoretical studies regarding the behavior of AlCu₄Mg₁ aluminum alloy after a heat treatment. The methodology has been proposed to study improvements in AlCu₄Mg₁ aluminum alloy in the process of heat treatment, which included the following steps: (1) adopting the heat treatment technology for the specified alloy, (2) choosing the necessary heat treatment installations to perform the heat treatment of the specified alloy, (3) choosing tools and machines used to study the mechanical characteristics, and (4) planning the experiment and analytical interpretation of the results. On the basis of these experiments and the obtained regression equation, we performed a theoretical study with the aim to determine the heating parameters for quenching and aging in order to obtain a specified stress needed for application of this alloy. We considered two cases for this theoretical study: (1) the stress and quenching temperatures were fixed and we determined the aging temperature; (2) the stress and aging temperatures were fixed and we determined the quenching temperature. Using the determined equations, we assumed the definite characteristics needed for the working part after treatment and calculated the parameters for quenching and artificial aging in the process of the heat treatment. Note that the calculated temperatures should be in the standard limits for the studied alloy. In conclusion, an algorithm was proposed for the process of the optimum heat treatment in order to obtain the necessary properties of the working parts.     

Tribological Behavior of Aluminum Alloy AlSi10Mg-TiB<Subscript>2</Subscript> Composites Produced by Direct Metal Laser Sintering (DMLS)

Direct metal laser sintering (DMLS) is an additive manufacturing technique for the production of parts with complex geometry and it is especially appropriate for structural applications in aircraft and automotive industries. Aluminum-based metal matrix composites (MMCs) are promising materials for these applications because they are lightweight, ductile, and have a good strength-to-weight ratio This paper presents an investigation of microstructure, hardness, and tribological properties of AlSi10Mg alloy and AlSi10Mg alloy/TiB₂ composites prepared by DMLS. MMCs were realized with two different compositions: 10% wt. of microsize TiB₂, 1% wt. of nanosize TiB₂. Wear tests were performed using a pin-on-disk apparatus on the prepared samples. Performances of AlSi10Mg samples manufactured by DMLS were also compared with the results obtained on AlSi10Mg alloy samples made by casting. It was found that the composites displayed a lower coefficient of friction (COF), but in the case of microsize TiB₂ reinforcement the wear rate was higher than with nanosize reinforcements and aluminum alloy without reinforcement. AlSi10Mg obtained by DMLS showed a higher COF than AlSi10Mg obtained by casting, but the wear rate was higher in the latter case.     

Crystal Structure Peculiarities of Martensite in the Ni<Subscript>47</Subscript>Mn<Subscript>42</Subscript>In<Subscript>11</Subscript> Alloy that Underwent Forward and Reverse Phase Transformations

The martensite structure of the Ni₄₇Mn₄₂In₁₁ alloy has been studied, and crystallographic peculiarities of the structure realized after ten cyclic forward and reverse phase transformations have been shown. Each cycle includes the heating to a temperature corresponding to the existence of austenite and subsequent cooling to cryogenic temperatures. It was found that (107)-twinned martensite crystals can contact not only on the (10\(\bar 7\)) plane, which, being the symmetry axis for the crystals, is not among the close-packed planes, but also on the (12\(\bar 7\)) plane, which is among close packed planes but is not the symmetry axis.     

On the temperature behavior of a tensoresistive effect in the amorphous Fe<Subscript>80</Subscript>B<Subscript>14</Subscript> alloy

Investigation of the temperature behavior of the coefficient of tensoresistance π of the amorphous Fe₈₆B₁₄ alloy in a temperature range from room temperature to the crystallization temperature has been carried out. It has been revealed that below the Curie temperature T _C, in the interval of existence of elinvar properties, π in this alloy increases only weakly, with a temperature coefficient of 4 × 10^?4 K^?1. At T > T _C, a stronger temperature increase of π is observed. An analysis performed has shown that the most probable reason of the observed temperature changes in π was a temperature-induced change in Young’s modulus of the alloy. It has been shown that during crystallization the coefficient of tensoresistance π decreases with increasing amount of crystalline phases in the alloy.     

Dilatometric analysis of the process of the nanocrystallization of Fe<Subscript>72.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>2</Subscript>Mo<Subscript>1.5</Subscript>Si<Subscript>14</Subscript>B<Subscript>9</Subscript> soft magnetic alloy

The process of the nanocrystallization of magnetically soft Fe_72.5Cu₁Nb₂Mo_1.5Si₁₄B₉ alloy has been studied using dilatometry and thermomagnetic analysis, together with structural investigations. It has been shown that the amount of nanocrystalline phase precipitated upon heating of the amorphous precursor is in good agreement with a shortening of the ribbon length in the course of crystallization. Thermal expansion at the different stages of heating and cooling depends on the structural and phase states, as well as on the magnetic state of the alloy. The numerical value of the coefficient of linear thermal expansion decreases with an increase in the fraction of the ferromagnetic crystalline phase.     

Corrosive wear behavior of 7075 aluminum alloy and its composite containing Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles

Corrosive wear behavior of 7075 aluminum alloy and a composite containing 0.10 volume fraction of alumina particles (VFAP) has been evaluated. Transient current (TC) generated as a result of impacting a rotating cylindrical electrode immersed in a 0.1M NaCl solution with a Vickers diamond hardness indenter has been used to measure the corrosive wear response. Age hardenable 7075 alloy shows TC values that are sensitive to prior solutionizing time. The effect of alumina particles in a 7075 aluminum alloy matrix has been studied by comparing the TC values of a monolith along with composites under almost identical experimental conditions. The role of microstructural features associated with composites, such as dislocations generated after solutionizing treatment and during the corrosive wear process, has been observed with the help of near surface microstructures through transmission electron microscopy (TEM). Deformation induced dislocations, as well as those that are due to differences in the coefficient of thermal expansion (CTE) values between the particles and the matrix during solutionizing, have been attributed to the experimentally observed TC values. They may also be affected by the aging response of the monolith and composites, depending on solutionizing time.     

Electrochemical corrosion behaviors of amorphous Co<Subscript>69</Subscript>Fe<Subscript>4.5</Subscript>Ni<Subscript>1.5</Subscript>Si<Subscript>10</Subscript>B<Subscript>15</Subscript> alloy

The corrosion behavior of an amorphous Co₆₉Fe_4.5Ni_1.5Si₁₀B₁₅ alloy ribbon was examined as a function of solution temperature (15 °C to 55 °C) and pH (3 to 11). The results of potentiodynamic polarization tests in H2SO4 solution, NaCl solution, and HCl + NaOH solution at various levels of pH showed that the corrosion resistance for the alloy ribbon significantly deteriorated with increasing temperature and decreasing pH for given conditions. The Co₆₉Fe_4.5Ni_1.5Si₁₀B₁₅ alloy was actively dissolved in solutions at pH 3 to 9 but passivated in a solution at pH 11. By comparison of the corrosion behaviors of Co₆₉Fe_4.5(Nb,Cr,Ni)_1.5Si₁₀B₁₅ alloys in the solution at pH 11, Ni was considered to contribute less in improving the corrosion resistance of the alloy than did Cr and Nb.     

Dissolution of Eutectic β-Mg<Subscript>17</Subscript>Al<Subscript>12</Subscript> Phase in Magnesium AZ91 Cast Alloy at Temperatures Close to Eutectic Temperature

Knowledge on the dissolution kinetics of β_-eut phase in cast Mg AZ91 alloy at temperatures close to the eutectic temperature is very useful for various processes of the alloy. In the present study, dissolution of β_-eut phase has been investigated experimentally and considered theoretically. Results have confirmed that the kinetics of β_-eut dissolution is basically diffusion controlled. Optimum times for dissolution heat treatment practice of different sizes of cast microstructure which are cooling rate dependant during casting could be suggested based on the present calculation. For fusion welding of the alloy, the present results indicate the difficulty of having a heating rate lower than the critical value (“critical heating rate”) for a significant reduction of the phase to avoid constitutional liquation.     

Tribological Behavior of Babbitt Alloy Rubbing Against Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and Steel Under Dry Friction Condition

The tribological behavior of Babbitt alloy rubbing with Si₃N₄ ball and steel ball with various sliding speeds at dry friction condition was investigated. It was found that B88 alloy rubbing with Si₃N₄ ball and steel ball possesses a low sliding wear resistance at dry friction. The wear rate is above 10^?4 mm³/Nm, and the friction coefficient is from 0.2 to 0.4. At low sliding speed of 0.05-0.1 m/s, the mainly wear mechanisms are microgroove and fatigue wear, while at high sliding speed of 0.5 m/s, the wear mechanisms depend on plastic deformation and delamination. The high wear rate indicates that it is needed to prevent Babbitt alloy from working at dry friction conditions, while the low friction coefficient suggests that it is not easy to the occurrence of cold weld.     

Tensile and wear properties of rolled Al5Mg-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> or C particulate composites

Al5Mg alloy matrix composites reinforced with different percentages of Al₂O₃ (60 μm) or C (90 μm) particulates were prepared by the vortex method. The composites were then subjected to hot or cold rolling with different reduction ratios. The microstructures of the rolled composites revealed that the matrix grains moved around the particulate causing deformation. By continuing deformation, the particulates rearranged themselves in the matrix, leading to lensoid distortion. It was found that the addition of Al₂O₃ or C particulates increased the 0.2% proof stress and reduced both the tensile strength and ductility, compared with the monolithic alloy. Scanning electron microscopy (SEM) fractographic examinations showed that the composites reinforced with Al₂O₃ particulates failed through particulate fracture and matrix ligament rupture. However, the failure of the composites reinforced with C particulates was through particulate decohesion, followed by ductile failure of the matrix. Abrasive wear results showed that the wear rate of the Al5Mg alloy decreased with the addition of C particulates. However, increasing the volume fraction of C particulates did not have a prominent effect on the wear rate. The composites reinforced with Al₂O₃ particulates exhibited a higher wear rate than that of the unreinforced alloy. Furthermore, addition of both C and Al₂O₃ particulates into the Al5Mg matrix alloy did not significantly improve the wear resistance. For all composites studied in this work, hot or cold rolling had a marginal effect on the wear results.     

High-pressure-torsion deformation of melt-spun Nd<Subscript>9</Subscript>Fe<Subscript>85</Subscript>B<Subscript>6</Subscript> alloy

The effect of severe plastic deformation by high-pressure torsion (HPT) at room temperature and subsequent annealing on the magnetic properties and structural transformations of the melt-spun alloy (MSA) Nd₉Fe₈₅B₆ is studied. The melt-spun ribbons in three structural states, such as nanocrystalline, mixed amorphous-nanocrystalline, and quasi-amorphous, have been subjected to deformation. In the nanocrystalline alloy, HPT leads to the decomposition of part of the Nd₂Fe₁₄B phase into the amorphous phase and α-Fe nanocrystals. The deformation of the alloy in the quasi-amorphous state leads also to the precipitation of a great amount of α-Fe nanocrystals; in this case, the amorphous matrix is depleted of iron. During the HPT of the MSA in the mixed amorphous + nanocrystaline state, both structural transformations occur. The annealing of deformed samples at above 500°C restores the two-phase (Nd₂Fe₁₄B + α-Fe) nanocrystalline state. This is accompanied by increasing magnetic hysteretic properties. The HPT has been found to suppress the formation of nonequilibrium magnetically soft phases, such as NdFe₇ and Nd₂Fe₂₃B₃, that precipitate upon annealing of the melt-spun amorphous alloy. This promotes the formation of an optimum nanocrystalline structure of the α-Fe/Nd₂Fe₁₄B composite material and an increase in its magnetic hysteretic properties because of enhancement of the intergranular exchange interaction. Compact micromagnets 6–15 mm in diameter and 0.2 mm thick, which were prepared from the Nd₉Fe₈₅B₆ alloy using HPT and subsequent annealing, exhibit the following characteristics: B _r = 11.4 kG, H _c = 5.4 kOe, and (BH)_max = 17.1 MG Oe.     

Microstructure properties and microhardness of rapidly solidified Al<Subscript>64</Subscript>Cu<Subscript>20</Subscript>Fe<Subscript>12</Subscript>Si<Subscript>4</Subscript> quasicrystal alloy

This paper presents differences in the microstructure and microhardness properties of conventional casting (ingot) and rapidly solidified Al₆₄Cu₂₀Fe₁₂Si₄ quasicrystal (QC) alloys. The phases present in the Al₆₄Cu₂₀Fe₁₂Si₄ ingot alloy were determined to be icosahedral quasicrystalline (IQC) Ψ-Al₆₅Cu₂₀Fe₁₅, cubic β-AlFe, tetragonal θ-Al₂Cu, and monoclinic λ-A1₃Fe₄ phases, whereas only IQC Ψ-Al₆₅Cu₂₀Fe₁₅ and cubic β-AlFe phases were identified in the rapidly solidified alloy. The microhardness value of the melt spun alloy was measured to be approximately 790 kg/mm². Microhardness increases with increasing solidification rates.     

Thermoelastic martensitic transformations,mechanical properties,and shape-memory effects in rapidly quenched Ni<Subscript>45</Subscript>Ti<Subscript>32</Subscript>Hf<Subscript>18</Subscript>Cu<Subscript>5</Subscript> alloy in the ultrafine-grained state

Methods of transmission and scanning electron microscopy and chemical microanalysis, electron diffraction, and X-ray diffraction were used to study the structure and the chemical and phase composition of ribbons of the four-component quasi-binary alloy Ni₄₅Ti₃₂Hf₁₈Cu₅. The influence of the synthesis regimes and subsequent heat treatment of the alloy on the formation of the amorphized state and ultrafine-grained structure has been determined. The critical temperatures of the devitrification and of the _B2 ? _B19' thermoelastic martensitic transformation have been established based on the data of the temperature dependences of the electrical resistivity. The lattice parameters of the _B2 and _B19' phases and the (Ti,Hf)₂Ni phase have been determined by X-ray diffraction. The mechanical properties of the alloy were determined in tensile tests, and the shape-memory effects in the ribbons of the alloy were measured using bending tests.     

Cup-shaped functionally gradient NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-based cermet inert anodes for aluminum reduction

Application of inert anode and wet-table cathode technology for aluminum reduction will result in significant energy and environmental benefits, so it has been a research focus for several decades. The candidate as inert anode concentrates on oxide ceramic, cermet, and alloy. This paper reviews briefly the research progress and presents the achievements of Central South University, Changsha, China, in developing an NiFe₂O₄-based cermet inert anode, which includes the preparation and optimization of material performance, the joint between the cermet anode and metallic bar, as well as the results of electrolysis testing for a large inert anode group. At the same time, the problems for NiFe₂O₄-based cermet inert anode faced are discussed.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles on the microstructure and sliding wear of 7075 Al alloy manufactured by squeeze casting method

Aluminum (Al) alloy 7075 reinforced with Al₂O₃ particles was prepared using the stir casting method. The microstructure of the cast composites showed some degree of porosity and sites of Al₂O₃ particle clustering, especially at high-volume fractions of Al₂O₃ particles. Different squeeze pressures (25 and 50 MPa) were applied to the cast composite during solidification to reduce porosity and particle clusters. Microstructure examinations of the squeeze cast composites showed remarkable grain refining compared with that of the matrix alloy. As the volume fraction of particles and applied squeeze pressure increased, the hardness linearly increased. This increase was related to the modified structure and the decrease in the porosity. The effect of particle volume fraction and squeeze pressure on the dry-sliding wear of the composites was studied. Experiments were performed at 10, 30, and 50 N with a sliding speed of 1 m/s using a pin-on-ring apparatus. Increasing the particle volume fraction and squeeze pressure improved the wear resistance of the composite compared with that of the monolithic alloy, because the Al₂O₃ particles acted as load-bearing constituents. Also, these results can be attributed to the fact that the application of squeeze pressure during solidification led to a reduction in the porosity, and an increase in the solidification rate, leading to a finer structure. Moreover, the application of squeeze pressure improved the interface strength between the matrix and Al₂O₃ particles by elimination of the porosity at the interface, thereby providing better mechanical locking.