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.     

Development of new magnesium based alloys and their nanocomposites

In the present study, 1 and 2 wt.% of aluminum were successfully incorporated into magnesium based AZ31 alloy to develop new AZ41 and AZ51 alloys using the technique of disintegrated melt deposition. AZ41-Al₂O₃ and AZ51-Al₂O₃ nanocomposites were also successfully synthesized through the simultaneous addition of aluminum (1 and 2 wt.%, respectively) and 1.5 vol.% nano-sized alumina into AZ31 magnesium following same route. Alloy and composite samples were then subsequently hot extruded at 400 °C and characterized. Microstructural characterization studies revealed equiaxed grain structure, reasonably uniform distribution of particulate and intermetallics in the matrix and minimal porosity. Physical properties characterization revealed that addition of both aluminum and nano-sized alumina reduced the coefficient of thermal expansion of monolithic AZ31. The presence of both Al and nano-sized Al₂O₃ particles also assisted in improving overall mechanical properties including microhardness, engineering and specific tensile strengths, ductility and work of fracture. The results suggest that these alloys and nanocomposites have significant potential in diverse engineering applications when compared to magnesium AZ31 alloy.     

A new technology for the production of aluminum matrix composites by the plasma synthesis method

Aluminum matrix composites were produced via the plasma injection of reinforcing particulates into aluminum melts stirred electromagnetically. In this process, a metallic wire supplied to the active zone of plasma torch disintegrated into fine metallic particles. In the plasma arc, the particles are heated above the melting point and accelerated to close to sonic speed, which helps with the incorporation of the particles into the melt. In this study, the possibility of producing aluminum matrix composites reinforced by intermetallic compound particles via plasma synthesis is demonstrated.     

Processing and response of aluminum-lithium alloy composites reinforced with copper-coated silicon carbide particulates

Lithium-containing aluminum alloys have shown promise for demanding aerospace applications because of their light weight, high strength, and good damage tolerance characteristics. Additions of ceramic reinforcements to an aluminum-lithium alloy can significantly enhance specific strength, and specific modulus while concurrently offering acceptable performance at elevated temperatures. The processing and fabrication of aluminum-lithium alloy-based composites are hampered by particulate agglomeration or clustering and the existence of poor interfacial relationships between the reinforcing phase and the matrix. The problem of distribution of the reinforcing phase in the metal matrix can be alleviated by mechanical alloying. This article presents the results of a study aimed at addressing and improving the interfacial relationship between the host matrix and the reinforcing phase. Copper-coated silicon carbide particulates are introduced as the particulate reinforcing phase, and the resultant composite mixture is processed by conventional milling followed by hot pressing and hot extrusion. The influence of extrusion ratio and extrusion temperature on microstructure and mechanical properties was established. Post extrusion processing by hot isostatic pressing was also examined. Results reveal the increase in elastic modulus of the aluminum-lithium alloy matrix reinforced with copper-coated SiC to be significantly more than the mechanically alloyed Al-Li/SiC counterpart. This suggests the possible contributions of interfacial strengthening on mechanical response in direct comparison with a uniform distribution of the reinforcing ceramic particulates.     

Mechanical Properties of Squeeze-Cast A356 Composites Reinforced With B4C Particulates

In this study, different volume fractions of B₄C particles were incorporated into the aluminum alloy by a mechanical stirrer, and squeeze-cast A356 matrix composites reinforced with B₄C particles were fabricated. Microstructural characterization revealed that the B₄C particles were distributed among the dendrite branches, leaving the dendrite branches as particle-free regions in the material. It also showed that the grain size of aluminum composite is smaller than that of monolithic aluminum. X-ray diffraction studies also confirmed the existence of boron carbide and some other reaction products such as AlB₂ and Al₃BC in the composite samples. It was observed that the amount of porosity increases with increasing volume fraction of composites. The porosity level increased, since the contact surface area was increased. Tensile behavior and the hardness values of the unreinforced alloy and composites were evaluated. The strain-hardening behavior and elongation to fracture of the composite materials appeared very different from those of the unreinforced Al alloy. It was noted that the elastic constant, strain-hardening and the ultimate tensile strength (UTS) of the MMCs are higher than those of the unreinforced Al alloy and increase with increasing B₄C content. The elongation to fracture of the composite materials was found very low, and no necking phenomenon was observed before fracture. The tensile fracture surface of the composite samples was indicative of particle cracking, interface debonding, and deformation constraint in the matrix and revealed the brittle mode of fracture.     

熔铸-原位反应喷射成形金属基复合材料制备新技术

研究开发了一种喷射成形金属基复合材料制备新技术———熔铸－ 原位反应喷射成形技术。该技术的突出优点是： 解决了颗粒损失和颗粒在合金基体中分布不均匀的问题; 合金的熔炼、颗粒的生成以及喷射成形金属基复合材料的制备同步进行, 明显缩短了复合材料的制备工艺流程, 降低了材料的制备成本。利用该技术制备了３ ％ ＴｉＣ／Ａｌ 复合材料。研究表明, ＴｉＣ 颗粒在铝基体中分布均匀, 制备的３ ％ ＴｉＣ／Ａｌ 复合材料组织致密     

摩擦速度对原位自生钢基复合材料Fe(Ti,W,Cr,V,Nb)Cp磨损性能的影响

用铸造的方法制备了原位自生复合碳化物(Ti,W,Cr,V,Nb)Cp增强钢基复合材料(In-situMMCs),并对该复合材料的高速磨损性能及磨损机理进行了研究。结果表明,原位自生复合材料中自生碳化物颗粒细小、圆整、分布均匀,自生碳化物体积分数达到42.8%;在低速150N载荷下,自生复合材料的耐磨性能随着自生碳化物体积分数的增加而提高;摩擦系数随摩擦速度的增大先减少后增大,自生碳化物体积分数大的自生复合材料的摩擦系数先快速减小后慢速增大,磨损率先减小后迅速增加。     

粉末冶金制备颗粒增强5052铝基复合材料的压力加工工艺研究

以SiC和Al2O3颗粒为增强体、5052铝合金粉末为基体材料，采用粉末冶金法制备了颗粒增强铝基复合材料，实．验研究了影响冷压坯致密度的主要因素，发现压坯长径比和粉末粒度组成对致密度影响较大。实验结果表明。与常规烧结 热挤压工艺相比，模内热压烧结 热挤压能够获得具有更高强度的材料。热挤压还可使坯料进一步致密化，改善颗粒分布均匀性．从而提高材料性能。     

碳化硅颗粒增强Al基复合材料的新型制备工艺

综述了碳化硅增强铝基复合材料的几种主要制备工艺,重点阐述了高能超声半固态复合法制备SiCp／Al复合材料。首先用渗流法制备SiC体积分数高的SiCp／Al预制块,进行SiC预分散,然后将预制块加入处于半固态温度条件下的铝合金熔体中,最后导入超声波进行搅拌。此法很好地改善了增强颗粒与基体之间的润湿性,使SiC在基体中均匀分布。     

Effect of Hot Working on Structure and Tribological Properties of Aluminium Reinforced with Aluminium Oxide Particulates

Al-Al₂O₃ (18%) composite was prepared by stir-cast melt technique. The microstructures showed uniform distribution of particulates, dispersed in the matrix. There exists discontinuity (~0.25???m) in the interface between particulates and matrix. The composite was hot forged. Hot working resulted in fine recrystallized microstructure with particulates dispersed along grain boundaries. Formation of pancake microstructure with some inhomogeneity in the microstructure along three faces of the forged composite was observed. The discontinuity across the interface between Al-Al₂O₃ was reduced to 0.125???m after forging. The as-cast and forged Al-Al₂O₃ composites showed higher wear resistance than pure Al. In lubricant media, there was no significant wear observed for either the as-cast or forged composite, whereas Al had shown higher wear at 50?N load.     

Trace Element Effects on Al-SiC Interfaces

Compatibility between the matrix and the reinforcement is one of the most important criteria in the development of composite materials. A dequate bonding between the matrix and the fibers is essential to enable maximum loading of fibers. In choosing a reinforcement for a matrix, any reaction between the matrix and the reinforcemnt should leave the properties of both materials unchanged. Thus, a study of the compatibility between the matrix and the reinforcement, as well as the interface between the two, is essential in developing adequately engineered materials. This paper examines the characteristics of the interfaces between aluminum and silicon carbide, with an emphasis on the effect of impurity elements in a commercial Al 1100 alloy. It appears that the silicon content in the 1100 alloy slows down the interfacial reaction. Thermodynamic considerations have revealed that although Al₄C₃ may not always be one of the reaction products, SiC surfaces will always be modified in contact with aluminum.     

超大挤压变形对钛合金增强镁基复合材料显微组织的影响

采用粉末冶金法制备了钛合金（Ti-6Al-4V）（质量分数，下同）颗粒增强MB15镁基复合材料，经225：1的超大比热挤变形后，借助光学显微镜（OM）、扫描电镜（SEM）和透射电镜（TEM）对其显微组织进行了研究。结果表明：钛合金颗粒沿挤压方向因塑性变形而被拉长，其增强效果得到提高；超大比热挤变形能够显著细化基体晶粒，并提高复合材料的组织均匀性；此外，原镁粉表面的氧化膜经超大比变形后得到了有效的碎化和分散，具有一定的弥散强化效果，因此可充当粉末冶金制备镁基复合材料的辅助增强相。     

Preparation and corrosion resistance of short basalt fiber/7075 aluminum composite

Aiming at the problem of poor corrosion resistance of aluminum alloy drill pipe materials in an alkaline environment, an innovative short basalt fiber/aluminum composite is prepared by vacuum hot-press sintering technique. Also, the corrosion behavior of the composites is investigated by hydrogen evolution and electrochemical tests. The results show that the corrosion resistance of 7075 aluminum alloy is significantly improved after adding 1.0 wt% short basalt fiber. According to the results of scanning electron microscopy and electrochemical impedance spectroscopy, the main component of basalt fiber, SiO₂, reacts with the aluminum matrix to produce a large amount of Al₂O₃. Meanwhile, Si atoms diffuse into the metal melt. This reaction improves the strength and density of the oxide film of the composite material, thereby improving its corrosion resistance.     

Microstructure and wear performance of Al5083/CeO2/SiC mono and hybrid surface composites fabricated by friction stir processing

Friction stir processing (FSP) was utilized to produce surface composites by incorporating nano-sized cerium oxide (CeO₂) and silicon carbide (SiC) particles individually and in combined form into the Al5083 alloy matrix. The study signified the role of these reinforcements on microstructure and wear behavior of the resultant surface composite layers. The wear characteristics of the resultant mono and hybrid surface composite layers were investigated using a pin-on-disc wear tester at room temperature. The microstructural observations of FSPed regions and the worn out surfaces were performed by optical and scanning electron microscopy. Considerable grain refinement and uniform distribution of reinforcement particles were achieved inside the nugget zone. All the composite samples showed higher hardness and wear resistance compared to the base metal. Among the composite samples, the hybrid composite (Al5083/CeO₂/SiC) revealed the highest wear resistance and the lowest friction coefficient, whereas the Al5083/SiC composite exhibited the highest hardness, i.e., 1.5 times as hard as that of the Al5083 base metal. The enhancement in wear behavior of the hybrid composites was attributed to the solid lubrication effect provided by CeO₂ particles. The predominant wear mechanism was identified as severe adhesive in non-composite samples, which changed to abrasive wear and delamination in the presence of reinforcing particles.     

Electrochemical corrosion behavior of Al–Si alloy composites reinforced with in situ TiB2 particulate

Understanding the corrosion behavior of TiB_2p‐reinforced aluminum matrix composites is crucial for their development as effective composites. In this work, corrosion characteristics of in situ TiB₂ particulate reinforced Al–Si alloy (A356) composite after T6 treatment are investigated by electrochemical techniques. The electrochemical impedance spectroscopy (EIS) reveals that the protection of nature film for the composites is worse than that for A356 alloy. Polarization experiments testify that the composites are susceptible to corrosion compared with their matrix alloys. Moreover, the corrosion resistance of the composites markedly decreases with increase in the TiB₂ content. The observations of the corrosion morphologies after polarization test show that the corrosion primarily occurs at the interdendritic sites with a large amount of TiB₂ particulates. Corrosion progress continues into the composite inner along the regions of α‐Al dendrite. The poor corrosion resistant properties of the composites are considered primarily due to the galvanic corrosion between noble TiB₂ reinforcements and more active aluminum matrix, as well as the weak protection of the defective nature film on the composite.     

Viscoplastic deformations and compressive damage in an A359/SiCp metal–matrix composite

Recent work by the authors has examined the high-strain-rate compression of a metal–matrix composite consisting of an A359 Al alloy matrix reinforced by 20 vol.% of silicon carbide particulates (SiC_p). The work-hardening that is observed in the experiments is much lower than that predicted by analytical and computational models which assume perfect particle–matrix interfaces and undamaged particles. In this work, we show that the discrepancy is a result of particle damage that develops within the A359/SiC_p composite under compression. The evolution of particle damage has been characterized using quantitative microscopy, and is shown to be a function of the applied strain. A simple analytical model that incorporates evolving damage within the composite is proposed, and it is shown that the analytical predictions are consistent with the experimental observations over a wide range of strain rates.     

Effect of ball milling the hybrid reinforcements on the microstructure and mechanical properties of Mg-(Ti + n-Al2O3) composites

In this study, composites containing pure magnesium and hybrid reinforcements (5.6 wt.% titanium (Ti) particulates and 2.5 wt.% nanoscale alumina (n-Al₂O₃) particles) were synthesized using the disintegrated melt deposition technique followed by hot extrusion. The hybrid reinforcement addition into the Mg matrix was carried out in two ways: (i) by direct addition of the reinforcements into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃) and (ii) by pre-synthesizing the composite reinforcement by ball milling and its subsequent addition into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃)_BM. Microstructural characterization revealed significant grain refinement due to reinforcement addition. The evaluation of mechanical properties indicated a significant improvement in microhardness, tensile and compressive properties of the composites when compared to monolithic magnesium. For the Mg-(5.6Ti + 2.5n-Al₂O₃) composite, wherein the reinforcements were directly added into the matrix, the improvement in strength properties occurred at the expense of ductility. For the Mg-(5.6Ti + 2.5n-Al₂O₃)_BM composites with pre-synthesized ball-milled reinforcements, the increase in strength properties was accompanied by an increase/retention of ductility. The observed difference in behaviour of the composites is primarily attributed to the morphology and distribution of the reinforcements obtained due to the ball-milling process, thereby resulting in composites with enhanced toughness.     

Effect of the B<Subscript>4</Subscript>C content on the structure and thermal expansion coefficient of the Al–5% Cu alloy-based metal-matrix composite material

The Al–5% Cu alloy-based metal-matrix composite materials reinforced with 5-μm B₄C particles have been produced using mechanical mixing-in method. A process of addition of the B₄C particles into the melt has been developed. A homogeneous distribution of the B₄C reinforcing particles in the metal-matrix composite matrix was obtained. Using X-ray diffraction analysis, the formation of Al₃BC and AlB₂ phases has been revealed at the interphase matrix/particle boundary, which indicates a good interaction in the phases. With increasing B₄C content in the matrix alloy, an insignificant increase in the porosity (from 1 to 3.1%) occurs. The average linear thermal-expansion coefficient is reduced from 24.5 to 22.6 × 10^–6 K^–1 in the temperature range of 20–100°C.     

Synthesis of Cr-doped APT in the evaporation and crystallization process and its effect on properties of WC-Co cemented carbide alloy

WC grain size has significant effect on WC-Co cemented carbide alloy properties. In order to inhibit WC grain growth during sintering process, grain growth-inhibitor Cr₃C₂ is usually added to tungsten carbide powder in advance through mechanical milling. While, homogeneous distribution of Cr₃C₂ in the tungsten carbide powder is difficult to achieve and result in abnormal growth of WC grains. For this purpose of growth-inhibitor uniform distribution, (CH₃COO)₃Cr is added into ammonium tungstate solution during evaporation and crystallization process to prepare Cr-doped APT powder, which can be used as precursor for ultrafine-grained WC-Co cemented carbide alloy preparation. Compared with conventional APT powder, the Cr-doped APT has smaller particle size and bulk density, moreover, chromium is evenly distributed within it. The Cr-doped APT is then used to produce Cr-doped tungsten powder, which also has smaller particle size than that of conventional tungsten powder. Cr-doped tungsten powder is subsequently prepared into tungsten carbide powder and WC-Co cemented carbide alloy through carbonization and sintering process, respectively. Compared with conventional WC-Co cemented carbide alloy, the obtained WC-Co cemented carbide alloy has smaller mean WC grain size (0.36 μm), and more uniform microstructure. Furthermore, the phenomenon of WC grain abnormal growth during sintering process is not observed, because the grain growth-inhibitor Cr₃C₂ is well dispersed in tungsten carbide and cobalt composite powder. Results show that the obtained WC-Co cemented carbide alloy presents better mechanical properties (HRA, bending strength, coercive force) than those of conventional WC-Co cemented carbide alloy. Accordingly, the novel addition of (CH₃COO)₃Cr during the evaporation and crystallization process is the key factor of ultrafine-grained WC-Co cemented carbide alloy production.     

化学成分对原位TiCp/Fe复合材料组织和性能的影响

系统地研究了化学成分对原位ＴｉＣｐ／Ｆｅ复合材料组织和性能的影响,并确定了该材料的最佳化学成分。结果表明：Ｔｉ是影响复合材料组织中ＴｉＣ颗粒形核率的关键因素,而Ｃ主要影响组织中ＴｉＣ颗粒的尺寸;在合金熔体中,加入一定量的Ｓｉ有利于ＴｉＣ颗粒的形成,而Ｍｎ主要用来细化珠光体基体。