Effects of heat treatment on phase contents and mechanical properties of infiltrated B_4C/2024Al composites

The B4C/2024Al composites were successfully produced by pressureless infiltration method, and the effects of heat treatment on phase content and mechanical properties were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and mechanical properties testing. The results show that phases of BnC/2024Al composites include B4C, Al, Al3BC, AlB2 and Al2Cu. The phase species remain unchanged; however, the phase content of the composites changes significantly after heat treatment at the temperature of 660, 700, 800 or 900 ℃ for 12, 24 or 36 h. It is found that the heat treatment results in not only considerable enhancement in hardness, but also reduction in bending strength of the composites. Heat treatment at 800 ℃ for 36 h does best to hardness of the composites, while at 700 ℃ for 36 h it is the most beneficial to their comprehensive mechanical properties.

Microstructures and mechanical properties of 2024Al/Gr/SiC hybrid composites fabricated by vacuum hot pressing

The 2024Al/Gr/SiC hybrid composite plates with 5%-10% SiC particles （volume fraction） and 3%-6% flaky graphite （Gr） （volume fraction） were fabricated by vacuum hot pressing and hot extrusion processing. The effects of SiC and Gr on the microstructures and mechanical properties of the composites aged at 160, 175 and 190℃ were studied by optical microscopy, scanning electron microscopy （SEM）, and hardness and tensile tests. The results indicate that the SiC particles have a more obvious effect on accelerating the aging response as compared with the Gr. Both the tensile strength and elongation are reduced by the Gr and SiC particles added into the matrix, while the Gr has a more negative influence on the elongation than the SiC particles. The tensile strength （ab）, yield stress （as） and elongation （δ） of the 2024Al/3Gr/10SiC composite aged at 165℃ for 8 h are 387 MPa, 280.3 MPa and 5.7%, respectively. The hybrid composites are characterized by ductile fracture, which is associated with the ductile fracture of the matrix and the tearing of the interface between the matrix and the particles.

Processing and mechanical properties of 2024 aluminum matrix composites containing Tungsten and Tantalum prepared by PM

The 2024 Al composites containing W, Ta were fabricated by powder metallurgy for their potential use as shielding material. W, Ta powders and gas-atomized 2024 Al aluminum powders were mixed by a ball mixer. The mixtures were consolidated by cold isostatic pressing (CIP) and then hot-extruded into full-density bars. The extruded bars were heat treated in T6 conditions. The microstructure and its relationship with the mechanical properties were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the particles of nonuniform size and irregular shape randomly disperse in the 2024 aluminum alloy matrix. The tensile tests show that an increase of tensile strength and decrease of elongation to failure of the heat treated composites compared with the extruded composites.

Microstructural characterization and mechanical properties of friction surfaced AA2024-Ag composites

The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing process. To carry out this investigation, Ag was added by 5.3, 10.6, and 16.0 wt.% to an AA2024 consumable rod by inserting holes in it. It was found that due to the strengthening by solid solution and the formation of precipitates and intermetallic containing Ag, the driving force for grain growth is reduced and consequently the grain size of the coating is decreased. After artificial aging heat treatment, the electrical conductivities of the coatings containing 0 and 16.0 wt.% Ag are increased by 4.15%(IACS) and decreased by 2.15%(IACS), respectively. While considering a linear relationship, it can be proposed that for a 1 wt.% Ag increase, the strength and hardness of the coating will be increased by 1.8% and 1.0%, respectively. It was established that the effect of Al6(Cu,Ag)Mg4 precipitate formation on strengthening is greater than that of Ag-rich intermetallic.

Diffusion Bonding of Silicon Carbide Particulate Reinforced 2024 Al Composites

A study has been made on diffusion bonding of SiCp/2024Ai composites by means of pure Al interlayer. In the condition of TB=843 K, PB=16 MPa, tB= 60 min, the diffusion bonded joint, with a shear strength of 235 MPa, was obtained when a 15 μm thick interlayer was used. The results of the shear testing and SEM indicate that fracture of the joint presented characteristics of ductile rupture.

Optimization of Process Parameters for in High-Energy Ball Milling of CNTs/Al2024 Composites Through Response Surface Methodology

The mathematical models are developed to evaluate the ultimate tensile strength( UTS) and hardness of CNTs / Al2024 composites fabricated by high-energy ball milling. The effects of the preparation variables which are milling time,rotational speed,mass fraction of CNTs and ball to powder ratio on UST and hardness of CNTs / Al2024 composites are investigated. Based on the central composite design( CCD),a quadratic model is developed to correlate the fabrication variables to the UST and hardness. From the analysis of variance( ANOVA),the most influential factor on each experimental design response is identified. The optimum conditions for preparing CNTs / Al2024 composites are found as follows: 1. 53 h milling time,900 r / min rotational speed,mass fraction of CNTs 2. 87% and Ball to powder ratio 25 ∶ 1. The predicted maximum UST and hardness are 273.30 MPa and 261.36 HV,respectively. And the experimental values are 283.25 MPa and256.8 HV,respectively. It is indicated that the predicted UST and hardness after process optimization are found to agree satisfactory with the experimental values.

Microstructural characterization and mechanical properties of functionally graded Al2024/SiC composites prepared by powder metallurgy techniques

Al2024/SiC functionally graded materials (FGMs) with different numbers of graded layers and different amounts of SiC were fabricated successfully by powder metallurgy method and hot pressing process. The effects of increasing SiC content and number of layers of Al2024/SiC FGMs on the microstructure and mechanical properties of the composite were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) analyses indicated that Al and SiC were dominant components as well as others such as Al4C3, CuAl2, and CuMgAl2

Corrosion Behavior of SiC_p/2024 Al Matrix Composites in 3.5 wt pct Sodium Chloride

The influences of volume fraction and particle size of SiC particulate reinforcements on the corrosion characteristics of SiCp/2024 Al metal matrix composites in aerated 3.5 wt pct NaCI aqueous solution were investigated. The electrochemical behavior was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy, the general corrosion behavior of the composites was studied further by immersion tests. The results showed that pitting susceptibility was about the same for the composites and the alloy. The corrosion potentials were also independent of SiC phase. The corrosion resistance for the composites decreased as the volume fraction increased or particle size decreased.

Microstructure and damping behavior of SiC_p/Gr/2024Al metal matrix composites by squeeze casting technology

SiCp/Gr/2024Al metal matrix composites were processed by squeeze casting technology. The microstructure of composites was observed by SEM and TEM, and the effects of graphite particulates and SiC particulates on the damping behaviors of composites were also investigated. The results show that the microstructure of composites was dense and homogeneous, without any interfacial reactivity among reinforcement/matrix interfaces. Compared with the damping capacity of 2024A1, the damping capacity of composites was enhanced significantly by addition of SiC or graphite particulates. The main damping mechanisms of SiCp/Al composites were ascribed to the dislocation damping, and those of SiCp/Gr/2024Al were attributed to the intrinsic damping and interface damping.

浇铸温度对1070A/2024铝合金铸轧复合薄板组织和性能的影响

采用立式双辊铸轧机制备了浇铸温度分别为670、680、690和700℃液-固铸轧1070A/2024铝合金复合板,通过金相显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)等检测设备以及剪切等试验方法,研究了浇铸温度对液-固铸轧1070A/2024铝合金复合板界面组织与性能的影响。结果表明:随着浇注温度的增加,覆层金属逐渐由细小的柱状晶变为粗大的等轴晶;当浇注温度为680℃时,界面处生成少量的金属间化合物,复合板界面结合得最紧密,此时复合界面的显微硬度和剪切强度分别为90.1 HV、86.8 MPa。

Damping capacity of in situ TiC_p/2024 composites

The internal friction and the damping behaviors of in situ TiC p/2024 composites have been investigated in comparison with those of 2024 matrix alloy. The results showed that the damping properties of the TiC p/2024 composites are superior to those of the matrix alloy and increase with increasing temperature and volume fraction of TiC. It was found that the damping properties were sensitive to frequency and temperature, and the dislocation damping and interface damping were the main factors which influence the damping behaviors of the composites. When the temperature was lower than 200 ℃, the dislocation damping was the main factor; when the temperature was higher than 200 ℃, the interface and boundary damping was the main factor.

Mixed rare earth metal conversion coatings on 2024 alloy and Al6061/SiC_p metal matrix composites

The processes of mixed rare earth metal (REM) conversion coatings on 2024 alloy and Al6061/SiC p metal matrix composites (MMC) were introduced. The coatings were examined to be honeycomb like feature by scanning electron microscope. X ray diffraction analysis revealed that the coatings are amorphous structure. The results of X ray photoelectron spectroscopy indicated that the mixed REM conversion coatings consist predominantly of Ce and O, the contents of other rare earth elements (such as La, Pr) are relatively low, the coatings are about 2～4 μm thickness with excellent adhesion and wearability. The results of mass loss test showed that the mixed REM conversion coatings produce corrosion resistant surface of 2024 alloy and Al6061/SiC p. [

铸轧速度对液-固铸轧1070A/2024铝合金复合板组织性能的影响研究

采用立式双辊铸轧机制备了铸轧速度分别为14 m/min、12 m/min、10 m/min、8 m/min的液-固铸轧1070A/2024铝合金复合板,使用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、硬度计和剪切实验等检测手段,研究了铸轧速度对液-固铸轧1070A/2024铝合金复合板材界面组织性能的影响。结果表明,随着铸轧速度的降低,复合界面处金属间化合物呈先增加后减少的变化趋势,复合界面硬度先增大后减小,铸轧速度为10 m/min时达到最高值129.5HV0.1;剪切强度呈先升高后降低而后再次升高的波浪状变化规律,铸轧速度为12 m/min时到达最大值80.7 MPa。

TiCP／2024复合材料的蠕变性能

研究了原位自生TiCP/2024(TiCP的质量分数为15%)复合材料在不同温度下的蠕变性能。结果表明,原位自生成TiCP/2024复合材料具有良好的抗高温蠕变能力。复合材料的密度变化量随着蠕变应变量和蠕变时间的增加而增加,并且在较低温度时的密度变化量高于较高温度时的密度变化量,当密度变化达到一定数量时产生的蠕变损伤即引起材料蠕变断裂。由于位错与第二相粒子的交互作用,提高了复合材料的抗蠕变能力。蠕变断口形貌表明蠕变过程产生的空穴多在一个颗粒或几个颗粒的聚集处形成,随着温度的升高,空穴不断扩展,直至最后发生塑性断裂,温度对蠕变过程具有显著的影响。

Characterization and evaluation of interface in SiC_p/2024 Al composite

35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface conditions were evaluated by tensile modules of elasticity and Brinell hardness measurement. The results show that the overall Si Cp/Al interface condition in this experiment is good and three kinds of Si Cp/Al interfaces are present in the composites, which include vast majority of clean planer interfaces, few slight reaction interfaces and tiny amorphous interfaces. The combination mechanism of Si C and Al in the clean planer interface is the formation of a semi-coherent interface by closely matching of atoms and there are no fixed or preferential crystallographic orientation relationships between Si C and Al. MgAl2O4 spinel particles act as an intermediate to form semi-coherent interface with SiC and Al respectively at the slight reaction interfaces. When the composite is aged at 190 °C for 9 h after being solution-treated at 510 °C for 2 h, numerous discoid-shaped and needle-shaped nanosized precipitates dispersively exist in the composite and are semi-coherent of low mismatch with Al matrix. The Brinell hardness of composites arrives peak value at this time.

Erosive Wear and Wear Mechanism of in situ TiC_P/Fe Composites

The base structure of in situ TiCp/Fe composites fabricated under industrial condition was changed by different heat treatments. Erosive wear tests were carried out and the results were compared with that of wear-resistant white cast iron. The results suggest that the wear resistance of the in situ TiCp/Fe composite is higher than that of wear-resistant white cast iron under the sand erosive wear condition. The wear mechanism of the wear-resistant white cast iron was a cycle process that base surface was worn and carbides were exposed, then carbides was broken and wear pits appeared. While the wear mechanism of in situ TiCp/Fe composite was a cycle process that base surface was worn and TiC grains were exposed and dropped. The wear resistance of in situ TiCp/Fe composite was lower than that of wear-resistant white cast iron under the slurry erosive wear condition. Under such circumstance, the material was not only undergone erosive wear but also electrochemistry erosion due to the contact with water in the medium. The wear behaviours can be a combination of two kinds of wear and the sand erosive wear is worse than slurry erosive wear.

Preparation and mechanical properties of SiC/2024 composite by semisolid casting

A SiC/2024 composite was made by semisolid casting. The wetting between SiC and Al matrix is improved by treating SiC particles at a high temperature, coating K2ZrF6, and adding Mg to the Al melt. An effective way to remove the gas around SiC particles was also found. Microstructures were observed under optical microscope (OM) and scanning electron microscopy (SEM). The results show that SiC particles and Al matrix are well bonded and no gaps or cavities around the particles are observed. SiC particles distribute homogeneously in the Al matrix. The existence of SiC particles results in the increase of wear resistance and strength.

Corrosion Behavior and Protection Efficiency of 2024Al and SiC_p/2024Al Metal Matrix Composite

The corrosion resistance of 2024 Al and SiC particle reinforced 2024 Al metal matrix composite (SiCp?024AI MMC) in 3.5% NaCl solution was investigated with electrochemical method and immersion test, and the corrosion protection of sulfuric acid anodized coatings on both materials was evaluated by electrochemical impedance spectroscopy. The results showed that the SiCp?024AI MMC is more susceptible to corrosion than its matrix alloy in 3.5% NaCI. For 2024AI, the anodized coating provides excellent corrosion resistance to 3.5% NaCI. The anodized coating on the SiCp?024AI provides satisfactory corrosion protection, but it is not as effective as that for 2024AI because the structure of the anodized layer is affected by the SiC particulates.

STUDIES ON MICROYIELD BEHAVIOR OF A SiCp/2024Al COMPOSITE

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In-situ TiC_P/Al Composites Prepared by TE/QP Method

An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents and the microstructure of the composites and the particle size of the reinforcement were analysed using X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results have shown that TiCp/Al composite with 40～70 vol. pct TiC particle reinforcement and high relative density can be directly obtained by TE/QP. TiC is the only reaction product when Al content in Al-Ti-C system is no more than 60 vol. pct, but Al3Ti phase will also form when Al content is more than 60 vol. pct. Increasing Al content prolongs the initial reaction time, reduces the highest reaction temperature and the reaction rate, and decreases the size of TiC particles. In addition, the microstructure of TiCp/Al composite and the structure of interface between TiCp and Al are studied using SEM and transmission electron microscopy （TEM）. The results show that the in-situ synthesized TiC particle has fcc cubic structure. The orientation between TiC particles and Al matrix can be described as （220）Al//（022）TiC and [112]Al//[011]TiC. Results of the mechanical property tests reveal that the ultimate strength （σ） and modulus （E） are 687 MPa and 142 GPa respectively when the Al content is 40 vol. pct. On contrary, 6 elongation increases by 3.2% with increasing Al content.