Effect of nano-silver on microstructure,mechanical and tribological properties of cast 6061 aluminum alloy

Al6061 matrix with different amounts of nano-silver (1% and 2%) was produced by stir-casting method. Produced samples were characterized by hardness, tensile, compression and wear tests. The hardness of the specimens at room temperature was measured by Brinnell hardness testing machine. The magnitude of hardness increased evidently with the function of the mass fraction of the nano-Ag particle. The polished specimens were examined with an optical microscope. The fracture surfaces of tensile and compressive specimens were further examined by scanning electron microscopy. Wear mechanisms were discussed based on the scanning electron microscopy observations of worn surface and wear debris morphology. There is an increase in compressive strength, ultimate tensile strength, elongation and wear resistance of the Al-Ag composites compared with base alloy. The execution of stir-casting technique is relatively homogenous and fine microstructure which improves the addition of reinforcement material in the molten metal. The results show that Al6061-nano-silver which is the best combination of hardness can replace the conventional material for better performance and longer life.     

固溶处理对TiB2/6061复合材料硬度及耐磨性的影响

采用氟盐法制备了TiB₂质量分数为3%的原位合成TiB₂/6061复合材料,研究了固溶温度和固溶时间对复合材料硬度和耐磨性能的影响。结果表明:TiB₂颗粒弥散分布在6061铝合金基体中,明显细化6061铝合金基体晶粒。当固溶温度一定时,随固溶时间延长,复合材料的硬度和耐磨性可获得明显提高,但固溶时间在6~10 h时,复合材料的性能变化不显著。当固溶时间一定时,随固溶温度升高,复合材料硬度和耐磨性呈现先上升后下降的趋势。3wt%TiB₂/6061复合材料经530 ℃×10 h固溶处理后,硬度和耐磨性能最佳,相较于铸态硬度值提高了79.5％,磨损量减少了59.1%。固溶处理后复合材料的磨损表面犁沟变细变浅,材料脱落现象减少。     

Tensile and fracture toughness properties of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The goal of this work was to evaluate the effects of particle size, particle volume fraction, and matrix strength on the monotonic fracture properties of two different Al alloys, namely T1-Al2124 and T1-Al6061, reinforced with silicon carbide particles (SiC_p). From the tensile tests, an increase in particle volume fraction and/or matrix strength increased strength and decreased ductility. On the other hand, an increase in particle size reduced strength and increased the composite ductility. In fracture toughness tests, an increase in particle volume fraction reduced the toughness of the composites. An increase in matrix strength reduced both K _crit and δ_crit values. However, in terms of K _Q (5%) values, the Al6061 composite showed a value similar to the corresponding Al2124 composite. This was mainly attributed to premature yielding caused by the high ductility/low strength of the Al6061 matrix and the testpiece dimensions. The effect of particle size on the fracture toughness depends on the type of matrix and toughness parameter used. In general, an increase in particle size decreased the K _Q (5%) value, but simultaneously increased the amount of plastic strain that the matrix is capable of accommodating, increasing both δ_crit and K _crit values.     

T6热处理对SiCp/Al复合材料摩擦磨损性能的影响

采用粉末冶金法制备出不同SiC颗粒体积分数(30%、35%和40%)的SiCp/Al复合材料。采用MMU-5GA微机控制真空高温摩擦磨损试验机对比研究SiCp/Al复合材料在不同体积分数以及T6热处理前后情况下平均摩擦因数和磨损率的变化,通过扫描电镜分析了SiCp/Al复合材料表面磨损形貌,探讨了摩擦磨损机理。试验结果表明,SiC颗粒体积分数在30%~40%变化时,随其体积分数增加耐磨性下降。SiC颗粒体积分数在30%~35%范围内,SiC颗粒与基体结合较好,SiC颗粒作为硬质点起到抵抗磨损和限制基体合金塑性变形产生磨损的双重作用;但SiC含量过多时,颗粒与基体的结合不紧密,磨损时颗粒极易脱落,复合材料耐磨性降低;T6热处理后复合材料的平均摩擦因数和磨损率均降低,这是由于热处理后试样强度及硬度提高,从而提高了试样的耐磨性;常温下复合材料在磨损初期的磨损机理主要以磨粒磨损为主,而在磨损期则为磨粒磨损与剥落磨损共存。     

Fabrication of Carbon Nanotube-Reinforced 6061Al Alloy Matrix Composites by an In Situ Synthesis Method Combined with Hot Extrusion Technique

Carbon nanotube(CNT)-reinforced 6061 Al alloy matrix composites were prepared by chemical vapor deposition(CVD) combined with hot extrusion technique. During the preparation process, the 6061 Al flakes obtained by ball milling of the 6061 Al spherical powders were subjected to surface modification to introduce a hydrophilic polyvinyl alcohol(PVA) membrane on their surface(6061Al@PVA) to bond strongly with nickel acetate [Ni(II)]. Then the6061Al@PVA flakes bonded with Ni(II) were calcined and reduced to Ni nanoparticles, which were then heat-treated at580 °C to remove PVA for obtaining even Ni/6061 Al catalyst. After that, the as-obtained Ni/6061 Al catalyst was employed to synthesize CNTs on the surface of the 6061 Al flakes by CVD. After hot extrusion of the CNT/6061 Al composite powders, the as-obtained CNT/6061 Al bulk composites with 2.26 wt% CNTs exhibited 135% increase in yield strength and 84.5% increase in tensile strength compared to pristine 6061 Al matrix.     

Comparison Between Wear Resistance of Functionally Graded And Homogenous Al-SiC Nanocomposite Produced by Friction Stir Processing (FSP)

In the present work, wear resistance of a homogeneous and functionally graded Al/SiC nanocomposite produced by friction stir processing was studied. According to the wear test results, the friction coefficient of the functionally graded nanocomposite was slightly less than that of the homogeneous nanocomposite (i.e., 0.7 compared to 0.8); this may be due to higher surface hardness of the functionally graded composite. In both cases, the weight loss increased with increasing applied loads; however, weight loss for the functionally graded nanocomposite was lesser under each applied load. Regarding surface studies by Scanning Electron Microscope (SEM) and Optical Microscope (OM), the functionally graded nanocomposite showed less micro-galling and other surface damages; this can be attributed to its surface hardness and high work of fracture.     

石墨粒度对6061铝性能的影响

选择6061A1为基体的铝合金,用同样质量分数的纳米级和微米级的石墨作为增强剂研究石墨粒度对6061A1性能的影响.分别从抗磨损、拉伸强度和阻尼性能几个方面对复合材料进行研究.结果表明,加入1%纳米石墨的复合材料耐磨损性能好于添加微米级石墨的复合材料;加入纳米石墨后复合材料的抗拉伸强度高于基体合金,而加入微米级石墨后复合材料的抗拉伸强度下降;加入石墨后复合材料的阻尼性能提高,但加入纳米级的石墨更具有优势.     

Centrifugal casting of functionally graded aluminium matrix composite components

Abstract

Centrifugal casting is one of the potential manufacturing techniques used for producing near net shaped components with improved properties. The emergence of new class of functionally graded materials has made it an important technique for the fabrication of engineering components and structures with graded property. The present paper describes the studies carried out on processing and characterisation of functionally graded Al matrix composites components based on Al–SiC ex situ and Al–Si in situ composites. The microstructural and mechanical characteristics of the composites are evaluated. In the case of Al–SiC functionally graded metal matrix composites discs, the particles are segregated gradiently towards the outer periphery of the casting exhibiting high strength and hardness towards the outer periphery. The Al–Si in situ composite cylinder shows the dispersion of primary Si particles towards the inner periphery of the casting which can lead to higher hardness and wear resistance.     

Al2O3-TiO2对铝合金表面激光熔覆NiAl涂层组织性能的影响

目的 进一步提高6061铝合金表面的硬度、耐磨性。方法 应用脉冲Nd:YAG激光器在6061铝合金表面制备了NiAl合金涂层和NiAl/Al2O3-TiO2复合涂层。通过SEM、X射线衍射仪系统研究了Al2O3-TiO2陶瓷相添加对NiAl熔覆层组织形貌、成分分布、物相组成的影响。利用HVS-1000硬度测试仪及HSR-2M高速摩擦磨损机,对熔覆层硬度分布及耐磨性进行测试分析。结果 Al2O3-TiO2陶瓷颗粒加入使涂层宏观成形质量明显提高,表面平整光滑、波纹均匀,熔覆层枝晶间距减小,组织结构明显细化。与NiAl熔覆层相比,在NiAl/Al2O3-TiO2复合涂层中,具有较高硬度的Al3Ni、Al3Ni2硬质相含量增大。同时,高硬度Al2O3和良好韧性的TiO2、NiTi金属间化合物在复合涂层内部形成。NiAl/Al2O3-TiO2复合涂层的显微硬度平均可达650HV0.2,相比NiAl涂层提高了300HV0.2;磨损体积仅为铝合金基体的1/9,相比NiAl涂层降低了35%。干摩擦条件下,NiAl/Al2O3-TiO2复合涂层的犁削、剥落现象显著降低。结论 在细晶强化、硬质相弥散强化及良好韧性的NiTi金属间化合物共同作用下,6061铝合金表面硬度和耐磨性得到显著提高。     

Wear Behavior of the Uniformly Dispersed Carbon Nanotube Reinforced 6061Al Composite Fabricated by Milling Combined with Powder Metallurgy

The uniformly dispersed carbon nanotubes (CNTs) reinforced 6061Al composites (CNT/6061Al) with different CNT concentrations were fabricated by powder metallurgy technology. It was found that the friction coefficient as well as wear rate decreased first and then increased as the CNT concentration increasing under 15 N as well as 30 N, and the minimum wear rate was achieved at the CNT concentration of 2 wt%. Adhesive wear and abrasive wear were the dominated wear mechanisms for the 1-2 wt% CNT/6061Al composites under 15 N and 30 N, while the delamination occurred on the wear surface at 3 wt% CNT. As the applied load increased to 60 N, the wear rate of composites increased dramatically. The wear mechanism transformed from abrasive wear to severe delamination wear, accompanied by the generation of wear debris with sharp edge due to the weaker anti-shearing strain capacity of CNT/6061Al composites.     

Co-electrodeposition and properties evaluation of functionally gradient nickel coated ZrO2 composite coating

For the first time, functionally electroless nickel plated ZrO₂ (NCZ) graded Ni-NCZ composite coating has been successfully co-electrodeposited from a bath with gradually increasing of stirring rate. Studies showed that co-electrodeposition in a bath with stirring rate of 250 r/min results in the maximum co-electrodeposited particle content and the best particle distribution. To produce NCZ graded Ni-NCZ composite coating, the stirring rate was continuously increased from 0 to 250 r/min. The electroplated coating had a continuous gradient increasing of co-electrodeposited NCZ content from substrate towards the surface. The results showed that with increasing the co-electrodeposited NCZ particles content in Ni matrix, microhardness increases from interface towards the surface of the coating. Little crystallite size of Ni matrix and higher co-electrodeposited hard particles content were recognized as the reasons of microhardness increasing. Bend test revealed that the functionally graded composite coating shows more excellent adhesion to the substrate compared with the ordinary distributed Ni-NCZ on the same substrate. This result is attributed to lower mechanical mismatch between coating and substrate in the functionally graded composite coating with respect to the uniformly distributed one. The results of wear resistance measurements reveal that wear resistance of functionally graded Ni-NCZ is higher than that of ordinary distributed composite coating.     

半固态热等静压Al/B4C复合材料液相流动行为与致密化机理

铝基碳化硼复合材料是一种重要的中子吸收材料。为了制备具有更高密度的铝基碳化硼材料,研究采用粉末冶金半固态热等静压方法制备了含量为30%碳化硼的铝基碳化硼材料,采用WANCE100型材料力学性能试验机和SIRION200型扫描电镜研究了复合材料的力学性能及显微形貌。结果表明：半固态热等静压工艺可制备获得接近理论密度的Al/B4C复合材料;虽然Al/B4C材料抗拉强度可提升至约300Mpa,但过高碳化硼含量也使得该材料脆性特征十分明显;研究同时采用间接的方法观察到了半固态工艺过程中生成的液相,该液相不仅可改善碳化硼颗粒与铝基体的结合性,在高温高压下液相的流动还起到填充复合材料内部空隙的作用。半固态热等静压工艺过程中产生的液相是复合材料密度和机械性能提升的主要原因。     

粒度和界面原子调控对SiC/Al复合材料强度的影响

SiC/Al复合材料作为一种轻质高强材料,因其优异的物理化学性能被外界广泛关注。本研究利用分子动力学方法,构建了不同SiC粒径的SiC/Al复合材料模型,根据拉伸变形模拟结果得出更小的SiC粒径有利于材料获得更高的抗拉强度。随着拉伸形变的逐渐增加,SiC颗粒在沿拉伸方向的两侧与Al基体发生分离从而产生孔隙,再从孔隙缺陷处产生位错形核并扩展至Al基体内形成塑性形变。在调节SiC/Al界面上C、Si的占位情况后,界面富Si的条件下结合更强,孔隙产生的难度增大从而对SiC/Al复合材料产生强化作用。     

Microstructures and properties of graphite and Al2O3 short fibers reinforced Mg-Al-Zn alloy hybrid composites

Graphite and Al2O3 short fibers reinforced Mg-Al-Zn alloy hybrid composites were fabricated by perform squeeze-infiltration route. The effects of the volume of graphite particles on the microstructure, mechanical properties and tr/bological behavior were investigated under the conditions of constant size of graphite particle and volume of Al2O3 short fiber. The results reveal that the uniform distribution of the reinforced graphite particles and Al2O3 short fiber can be obtained by this technique, and they have strong bonding with the metal matrix. Increasing graphite volume results in decrease in hardness, the ultimate tensile strength whereas the Al2O3 short fiber makes contribution to the increase in hardness of the composite. The composite exhibits good wear resistance, small wear mass loss and low coefficient of friction as compared with the metal matrix. The wear mechanisms transit from oxidation wear, abrasion wear into delamination wear as the applied load is increased, and a film of lubricant covering almost entire surface of specimen, is found to be formed, which separates the wear surfaces from metal to metal contact and thus improves the tribological properties.     

Aluminum-silicon carbide coatings by plasma spraying

An aluminum base composite (Al-SiC) powder has been developed for producing plasma sprayed coatings on Al and other metallic substrates. The composite powders were prepared by mechanical alloying of 6061 Al alloy with SiC particles. The concentration of SiC was varied between 20 and 75 vol%, and the size of the reinforcement was varied from 8 to 37 μm in the Al-50 vol% SiC composites. The 44 to 140 μm composite powders were sprayed using an axial feed plasma torch. Adhesion strength of the coatings to their substrates were found to decrease with increasing SiC content and with decreasing SiC particle sizes. The increase in the SiC content and decrease in particle size improved the erosive wear resistance of the coatings. The abrasive wear resistance was found to improve with the increase in SiC particle size and with the SiC content in the composite coatings.     

Mechanical Properties of Vermicular Graphite Cast Iron Processed by Selective Laser Surface Alloying with Ultra-fine ZrO_2 Ceramic Particulates

In this work, the mechanical properties and microstructures of vermicular graphite cast iron processed by selective laser surface alloying with ultra-fine ZrO_2 ceramic particulates were investigated. A particulate-reinforced metal matrix composite coating with the thickness of ~650 μm was fabricated by laser treatment on the sample surface. The particulates were uniformly distributed in the microstructure of the coating. The tensile strength and microhardness both increased with the particulate fraction, since more tensile load was transferred from the matrix to the reinforcement showing essential strengthening effect. The composite coating also sharply reduced the wear mass loss and thus improved the wear resistance.     

Superplastic behavior of PM SiCp/6061 aluminum alloy composites at high strain rates

The superplastic behavior of a powder-metallurgy processed 6061 Al composite was investigated as a function of SiC content increasing from 0% to 30% at 10% increments over a wide temperature range from 430°C to 610°C. The materials were found to be high-strain-rate superplastic. In the temperature range where grain boundary sliding (GBS) controlled the plastic flow, the strength of the composite was lower than that of the unreinforced matrix alloy even after compensating for grain size and threshold stress. This “particle weakening” was in contrast with the particle strengthening observed in the low temperature range where dislocation climb creep was found to control the plastic flow. In the GBS regime, the strength differential between the materials was a function of SiC content and temperature, which increased with the increase in SiC content and temperature. Strong Mg segregation was detected at interfaces between SiC and Al phases in the composites. Evidence for interfacial reaction reported in the Si₃N₄ reinforced 6061 Al composites could not be detected in the current composites. Extensive formation of whisker-like fibers was observed at the fractured surface of the tensile samples above the critical temperature where particle weakening begins to be exhibited. This result suggests the possibility that partial melting in the solute-enriched region near SiC interfaces is responsible for the particle weakening in the SiC reinforced 6061 Al composite.     

Al 2O 3 PARTICLE REINFORCED COPPER MATRIX COMPOSITE USING FOR CONTINUOUS CASTING MOULD

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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.     

添加NH_4AlO（OH）HCO_3原位生成Al_2O_3/Al复合材料的制备及其性能

碳酸铝铵与熔融的铝液反应原位生成颗粒增强铝基复合材料,对复合材料的力学性能和摩擦磨损行为进行研究。结果表明：在搅拌的铝熔体中碳酸铝铵发生分解反应生成γ-Al2O3;该原位反应的增强颗粒比直接添加的Al2O3在铝熔体中分布得更均匀;复合材料的密度和硬度随着增强相加入量的增加而提高,而强度则随着增强相加入量的增加而降低;磨损率随着增强相加入量的增加和载荷的增加而提高;原位反应生成的复合材料的力学性能和耐磨性明显优于直接添加Al2O3颗粒形成的复合材料的。