Investigation of Mechanical Properties and Dry Sliding Wear Behaviour of Squeeze Cast LM6 Aluminium Alloy Reinforced with Copper Coated Short Steel Fibers

LM6 aluminium alloy with 2.5–10 wt% of copper coated short steel fiber reinforced composites were prepared using squeeze casting process. Microstructure and mechanical properties viz., hardness, tensile strength and ductility were investigated. Dry sliding wear behaviour was tested by considering sliding distance and load. Fracture surface and worn surface were examined using field emission scanning electron microscope (FESEM). Hardness of composites increased with increasing wt% of fiber. Tensile strength of composites increased up to 19% for 5 wt% fiber composites. Further addition of fibers decreased the tensile strength of composites. Ductility of the composites decreased with the addition of fibers into the matrix. Wt% of fibers significantly decreased the weight loss, coefficient of friction and wear rate. Also the cumulative weight loss decreased up to 57% for 10 wt% of composites compared to LM6 aluminium alloy. Fracture surface of composite tensile specimen showed dimple formation and fiber pullout. Worn surface of matrix showed long continuous grooves due to local delamination on the surface. However, worn surface of composites showed fine and smooth grooves due to ploughing rather than local delamination. Copper coated steel fiber reinforcement in LM6 aluminium alloy exhibited better mechanical properties and wear resistance compared to matrix.     

Investigation on microstructure and tensile behaviour of stir cast LM13 aluminium alloy reinforced with copper coated short steel fibers using response surface methodology

Copper coated steel fibers reinforced LM13 aluminium alloy composites have been prepared using stir casting process. Experiments have been designed using response surface methodology by varying wt% of reinforcement (0–10), stirrer speed (350–800 rpm) and pouring temperature (700–800 °C). Microstructure, tensile strength and fracture surface of composites have been investigated. Analysis of variance, significance test and confirmation tests have been performed and regressions models have been developed to predict the tensile strength of composites. Response surface plots reveal that tensile strength of composites increases with increasing wt% of copper coated steel fibers reinforcement up to 6 wt%. Further increase in wt% of steel fibers decreases the tensile strength of composites. However tensile strength of composites increases with increasing stirrer speed due to the uniform and homogeneous dispersion of steel fibers in matrix. Optimum stir cast process parameters for obtaining higher tensile strength are found to be 5.9 wt% of reinforcement, 753 °C pouring temperature and stirrer speed of 633 rpm. Fracture mechanism is dominated by steel fiber pullouts in composites with higher wt% of reinforcement and dimples are observed in the surface of composites containing lower levels of wt% of reinforcement.     

Microstructural and Mechanical Characterization of as Weld and Aged Conditions of AA2219 Aluminium Alloy by Gas Tungsten Arc Welding Process

In this article, Welding of AA2219 aluminium alloy using Gas tungsten arc welding process (GTAW) and evaluation of metallurgical, mechanical and corrosion properties of the joints are discussed. The weld samples were subjected to ageing process at the temperature range of 195°C for a period of 5 h to improve the properties. AA2219 aluminium plates of thickness of 25 mm were welded using gas tungsten arc welding (GTAW) process in double V butt joint configuration. The input parameters considered in this work are welding current, voltage and welding speed. Tensile strength and hardness were measured as performance characteristics. The variation in the properties were justified with the help of microstructures. The same procedures were repeated for post weld heat treated samples and a comparison was made between as weld condition and age treated conditions. The post weld heat samples had better tensile strength and hardness values on comparing with the as weld samples. Fracture surface obtained from the tensile tested specimen revealed ductile mode of failure.     

Effect of Prior Oxidation on Tensile Properties of Bare and Al3Ti Diffusion Aluminide Coated Near α Titanium Alloy Titan 29A

The effect of prior oxidation, for various durations up to 2,000 h in air at 650 °C, on the room temperature tensile properties of uncoated and Al₃Ti diffusion aluminide coated near α Ti alloy, Titan 29A, has been evaluated. The tensile properties of the uncoated alloy deteriorated with oxidation. Oxidation for just 100 h caused 11–13 % decrease in yield strength (YS) and ultimate tensile strength (UTS) of the alloy. The uncoated alloy exhibited brittle fracture within the elastic regime at significantly lower stress after oxidation for 2,000 h. On the other hand, the strength of the coated alloy remained unaffected even after 2,000 h of oxidation and the YS and UTS was similar to that of the un-oxidized alloy. The ductility of the coated alloy, however, decreased with the increase in oxidation duration. Such differences in the tensile behavior of the uncoated and coated alloy can be ascribed to the beneficial effect of the Al₃Ti diffusion aluminide coating in preventing surface embrittlement in the alloy during oxidation.     

Effect of elevated temperature exposure on the structure,stability, and mechanical behavior of aluminum-stainless steel composites

The effect of elevated temperature exposure on subsequent ambient temperature tensile behavior of aluminum-stainless steel composities (V _f= 6.5 pct) has been studied. In particular, ambient temperature tensile yielding, flow, and fracture were correlated with the associated interface microstructures, matrix substructure, and fracture morphology in the as-pressed condition and following elevated-temperature exposure at 550°C (823 K) or 625°C (898 K) for 24 h (86.4 ks). Compared to the as-pressed condition, exposure at either temperature results in a small increase (?4 pet) in initial modulus, and a decrease in the level of residual stress (tensile) in the matrix; tensile stress-strain behavior in stage II (matrix plastic, reinforcement elastic) is essentially unaffected. Lower strength levels in stage III (matrix and reinforcement plastic) after exposure are due to premature cracking in the interface reaction zone, primarily a ternary (Fe, Cr) Al intermetallic, with associated notch effects on the wire reinforcement. Changes in fracture surface morphology of the composites confirm the degradation. Wires extracted from composites after hot pressing or following exposure at 550°C (823 K) possess a unique strength. Exposure at 625°C (898 K) leads to a bimodal distribution in the strength of extracted wires. In each condition, a matrix dislocation cell structure develops in stage III; the invariant form and size of the cell structure withV _f and distance from the matrix wire interface confirm isostrain conditions.     

Influence of Multiwalled Carbon Nanotubes on the Aging Behavior of AA 6061 Alloy Matrix Nanocomposites

The effect of multiwalled carbon nanotubes (MWCNT) with varying volume fractions on aging behavior of aluminium alloy 6061 matrix nanocomposites (MWCNTs/AA 6061) has been studied. The aging behavior of the developed nanocomposites has been evaluated at a temperature of 170 °C for different time intervals by means of Vickers hardness. Increase in the peak hardness by 32 and 27 % was observed by the addition of 2 wt% copper coated and uncoated MWCNTs for the aging time of 40 and 43 min as compared to base alloy with the peak hardness of 107 for the aging time of 55 min. The dramatic increase in the peak hardness of the nanocomposite within a short span of aging time is due to the generation of dislocations due to the difference in the co-efficient of thermal expansion between the AA6061 matrix and MWCNTs.     

Mechanical Properties and Microstructural Characteristics of Friction Welded Dissimilar Joints of Aluminium Alloys

Joining of similar and dissimilar combinations of aluminium alloys 2024 and 6061 were performed using friction welding technique. Microstructure, hardness and tensile properties of the joints were characterized. Microstructure of the alloy were found to change significantly across the joint such as fully deformed, partially deformed and undeformed regions due to deformation, frictional heat and alloy characteristics. Extensive fine grain size was observed in the fully deformed region and volume fraction of finer grains was higher in the alloy 2024 as compared to alloy 6061. Hardness was lower in the weld interface region of the similar joints of AA2024 and AA6061. The lower hardness in the dissimilar metal joint was observed in the heat affected zone of alloy 6061. The tensile strengths of the similar joints were 80 and 85% of respective base metal of alloys 2024 and 6061. The strength of the dissimilar metal joint was observed to be similar to the base metal strength of 6061 alloy. Tensile fracture occurred in the region of joints where lower hardness was observed. The maximum elongation were obtained in dissimilar joints of alloys and characterized by scanning electron microscope. It revealed deep dimple patterns unlike what was observed in similar joints.     

Mechanical Properties of Aluminium-Graphene Composite Synthesized by Powder Metallurgy and Hot Extrusion

The present work focuses on the development of multilayer graphene reinforced aluminium metal matrix composites by powder metallurgy followed by hot extrusion. Microstructure, grain size analysis and mechanical properties of hot extruded unreinforced aluminium and graphene reinforced aluminium composites are presented here. Microstructure shows uniform distribution of graphene throughout the matrix. Experimental results reveal significant increase in hardness as well as tensile strength of composite as compared to unreinforced aluminium. The improvements in properties are attributed to uniformly dispersed graphene sheets, an excellent interfacial bonding between graphene and aluminium matrix and grain refinement caused by the addition of graphene. Further, the strengthening mechanisms involved in the aluminum-graphene composite have been discussed. The fracture studies show the transition of ductile fracture in case of pure aluminium to brittle fracture in case of aluminium-graphene composites.     

The effect of cryogenic cooling on the tensile properties of metal-matrix composites

Tensile specimens machined from metal-matrix, oriented-fiber composites (aluminum alloy reinforced with high strength stainless steel wire) were heated to 260°C and cooled in air to produce a tensile residual stress state in the matrix. Some of the test pieces were cooled to the temperature of boiling nitrogen, held at temperature for fifteen minutes, and then air warmed to room temperature. All test pieces were subsequently strain cycled in tension and the resulting stress-strain behavior was recorded. The results indicated cryogenic refrigeration extended the first stage (totally elastic) behavior of these materials. It was shown that the beneficial effects of the cryogenic treatment resulted from an alteration of the residual stress state brought about by plastic flow of the matrix. Finally, it was shown that these effects could be computed by rigorous analytical methods.     

铜包覆石墨烯增强316L奥氏体不锈钢力学性能研究

采用分子水平混合和低速球磨的方法制备铜包裹石墨烯/316 L不锈钢复合粉体,通过放电等离子烧结制备石墨烯增强316 L奥氏体不锈钢复合材料,研究铜及石墨烯对复合材料密度、硬度和拉伸性能的影响,并对拉伸断口形貌进行了分析.结果表明:通过分子混合和球磨混合可制备铜包裹石墨烯与不锈钢均匀混合的复合粉体.烧结过程石墨烯结构保持完整.铜包裹石墨烯增强体可明显改善烧结不锈钢复合材料的密度、硬度、抗拉强度和屈服强度,使其分别提高3.6%、17.4%、35.8%和34.5%.     

Effect of environment on the thermal fatigue response of an SCS-6/Ti-24Al-11Nb composite

A study has been conducted examining the thermal fatigue characteristics of an α₂/SiC composite; in particular, SCS-6 reinforced Ti-24Al-11Nb (at. pct). The effort included the investigation of the effect of the environment by cycling coated and uncoated specimens in air and in an inert environment. Damage assessment was determined by postcycling room-temperature tension testing as well as by microstructural examination, including both optical microscopy and scanning electron microscopy (SEM). Significant reductions in postcycling tensile strength were observed for coated and uncoated specimens thermally cycled in air from 150 °C to 815 °C for 500 cycles, while no measurable loss of strength was found for specimens cycled in a low-pressure inert environment under otherwise identical conditions. The synergistic effect of residual stresses due to a coefficient of thermal expansion (CTE) mismatch and environment on the degradation of tensile properties of the thermally cycled composite is found to be the critical damage evolution mechanism for both coated and uncoated composites cycled in air. Residual stresses alone were found not to be critical in creating damage that could be tracked by a loss in residual strength.     

Influence of Powder-Chip Based Reinforcement on Tensile Properties and Fracture Behaviors of LM6 Aluminum Alloy

Tensile properties and fracture behaviors of silicon rich LM6 aluminum alloy were investigated in details for as cast alloy and modified by LM6 powdery-chip capsules. The obtained results showed that 20% modified LM6 cast composite ensured the excellent tensile properties (tensile strength of 203 MPa with 3.8% elongation). An impressive increase in the elongation (6.8%) was found for 25% modified cast composite with good ultimate tensile strength, 6.2% higher than unmodified (182 MPa). Characterization of the casts and fracture surfaces were carried out to study the effect of reinforcement particles. An influence of un-melted chip structure was observed inside the cavities and on fractured surfaces. The XRD results showed that cast consisted of inter-metallics of AlO₂, Al₂Si and Al₄Si. It was attributed to micro-cracks prevalently propagated along the broken eutectic silicon particles and some rejected solid particles on the fractured surfaces with ductile and inter-granular fracture. Debonding and cracking of silicon particles were also detected on the fractured surface of the specimens.     

Investigations on Dissimilar Weld of UNS S32205 DSS and ASTM A517 Steel

In the present research, microstructure and mechanical properties of 2205 duplex stainless steel/A517 quench and tempered low alloy steel dissimilar joint were investigated. For this purpose, gas tungsten arc welding was used with ER2209 filler metal. Characterizations were conducted by optical microscopy, scanning electron microscopy equipped with an energy dispersive spectroscopy and X-ray diffraction. Mechanical properties were evaluated in micro-hardness, tensile and impact tests. Microstructure in the weld zone included an austenitic continuous network in the matrix of primary ferrite. No brittle phases were formed in the weld metal and stainless steel heat affected zone (HAZ). The weld metal/A517 interface showed higher hardness than other regions. Tensile tests indicated that the values of the yield and tensile strength were 663 and 796 MPa, respectively. Impact tests indicated that the weld zone had almost the same impact energy as base metals. The minimum impact energy of 12 J was related to A517 HAZ. The results of scanning electron microscopy for fracture surfaces indicated that weld zone, 2205 HAZ and A517 HAZ had ductile, ductile–brittle and brittle fracture mode, respectively.     

The tensile properties of a graphite-fiber-reinforced Al-Si alloy

Room temperature uniaxial tensile tests have shown that composites of an Al-13 wt pct Si alloy and Thornel 50 graphite fibers have strengths greater than a theoretical value that was calculated on the basis of the law of mixtures. At 28 vol pct fibers, the average uniaxial tensile strength was found to be 106,000 psi, and several values between 130,000 and 144,000 psi were obtained. The modes of deformation and failure in the composites have been studied by the microexamination of polished surfaces and fractures of tested specimens. The reasons for the high strengths and the unusual modes of fracture that were observed cannot be explained on the basis of the presented data. Specimens of the composite have been thermally cycled between −193° and +20°C twenty times and others between −193° and +500°C twenty times. Tensile tests and microexamination of these thermally cycled specimens show that thermal cycling does not degrade the tensile properties of the composites or change their microstructure.     

Structure–Property Correlation of Al–SiC–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composites: Influence of Processing Temperatures

This paper deals with the change in the mechanical behaviour of aluminium alloy 6061 with different weight percentage of Silicon Carbide (SiC) and Alumina (Al₂O₃) ceramic powders and change in processing temperature. The crucial properties of this aluminium alloy are relatively light in weight, better corrosion resistance, wear resistance and have low production cost. These properties make them pleasant for different applications such as aerospace, defense, automotive sectors. The purpose of designing Metal Matrix Composite is to figure the desired qualities of metals and ceramics. The fabrication of the MMC was done by stir casting process. The tensile test, hardness test and impact test were performed on these composite samples to study the mechanical behaviour. The result shows that there is a significant increase in tensile strength for the samples that are processed at the temperature of 750 °C with a higher weight fraction of SiC. Also, the samples made at 850 °C exhibit better hardness and impact strength with increased content of alumina. The internal microstructure of the composites was analyzed by scanning electron microscope.     

Axial creep and stress-rupture of B-Al composites

Constant load creep and stress-rupture properties of boron and silicon carbide coated boron, BORSIC^®, filament reinforced aluminum alloys were measured at 300°, 400°, and 500°C. The mean stresses for 1000 hr rupture life at the three test temperatures were 96,000, 82,000, and 72,000 psi, respectively. Elongation in creep tests was checked by using scribed lines, and this technique indicated that grip-mounted extensometers were inadequate for precision measurement due to shear of aluminum in the grips. A maximum of 0.2 pct plastic elongation was measured, which corresponds to the creep properties of the filaments. Comparison of Borsic composite results with data for composites fabricated with uncoated boron filament showed that the short-time rupture strengths of the two materials were similar, but that the stress for rupture of the boron filament composites decreased much more rapidly with increasing rupture time than did the stress for rupture in the Borsic filament composites, due to degrading reactions of the uncoated boron with the matrix. Fracture analysis was performed using optical metallography and scanning electron microscopy. The analysis indicated that the major portion of filament failures in the region of the fracture surface at elevated temperatures initiated at the outer surface of the filament, whereas filament failures that initiated in the region of the core were more common in room temperature tensile specimens. The amount of plastic flow in the matrix increased markedly with increasing temperature, but filament pullout lengths were far less than those predicted by a simple shear-lag theory on the basis of the shear strength of the matrix.     

Microstructure and mechanical properties of Al-Mg-Mn-Zr-Er weld joints filled with Al-Mg-Mn-Zr and Al-Mg-Mn-Zr-Er weld wires

The Al-Mg-Mn-Zr-Er alloy sheets with a thickness of 4 mm were welded by TIG welding, the microstructures and mechanical properties of Al-Mg-Mn-Zr-Er alloy weld joints filled with F1.6 mm Al-Mg-Mn-Zr and Al-Mg-Mn-Zr-Er welding wires were studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, hardness testing and tensile mechanical properties testing. The result showed that, the tensile strength increased by 57 MPa and the coefficient of weld joint reached 0.8 when Al-Mg-Mn-Zr-Er welding wire was used as filling material. The tensile strength and elongation of weld joint filled with Al-Mg-Mn-Zr-Er welding wire were 19% and 85% higher those that of filled with Al-Mg-Mn-Zr welding wire respectively, which resulted from grain refinement strengthening and dispersion strengthening of Al₃Er.     

Optimization of mechanical properties of high-carbon pearlitic steels with Si and V additions

Systematic research has been undertaken on the effects of single and combined additions of vanadium and silicon on the mechanical properties of pearlitic steels being developed for wire rod production. Mechanical test results demonstrate that the alloy additions are beneficial to the mechanical properties of the steels, especially the tensile strength. Silicon strengthens pearlite mainly by solid-solution strengthening of the ferrite phase. Vanadium increases the strength of pearlite mainly by precipitation strengthening of the pearlitic ferrite. When added separately, these elements produce relatively greater strengthening at higher transformation temperatures. When added in combination the behavior is different, and substantial strength increments are produced at all transformation temperatures studied (550 °C to 650 °C). The addition of silicon and vanadium to very-high-carbon steels (>0.8 wt pct C) also suppresses the formation of a network of continuous grain-boundary cementite, so that these hypereutectoid materials have high strength coupled with adequate ductility for cold drawing. A wire-drawing trial showed that total drawing reductions in area of 90 pct could be obtained, leading to final tensile strengths of up to 2540 MPa in 3.3-mm-diameter wires.     

Mechanical properties of Fe-Si-B amorphous wires produced by in-rotating-water spinning method

Amorphous wires with high strength and good ductility have been produced in Fe-Si-B alloy system by the modified melt-spinning technique in which a melt stream is ejected into a rotating water layer. These wires have a circular cross section and smooth peripheral surface. The diameter is in the range of about 0.07 to 0.27 mm. Their Vickers hardness (H_v) and tensile strength (σ_f) increase with silicon and boron content and reach 1100 DPN and 3920 MPa, respectively, for Fe₇₀Si₁₀B₂₀, exceeding the values of heavily cold-drawn steel wires. Fracture elongation(ε _f ), including elastic elongation, is about 2.1 to 2.8 pct. An appropriate cold drawing results in the increase of σ_f and ε_f by about eight and 65 pct, respectively. This increase is interpreted to result from an interaction among crossing deformation bands introduced by cold drawing. The undrawn and drawn amorphous wires are so ductile that no cracks are observed, even after closely contacted bending. Further, it is demonstrated that the σ_f of the Fe₇₅Si₁₀B_l5 amorphous wire increases by the replacement of iron with a small amount of tantalum, niobium, tungsten, molybdenum, or chromium without detriment to the formation tendency of an amorphous wire. Such iron-based amorphous wires are attractive as fine gauge, high strength materials because of their uniform shape and superior mechanical qualities.     

Response of Phase Transformation Inducing Heat Treatments on Microstructure and Mechanical Properties of Reduced Activation Ferritic-Martensitic Steels of Varying Tungsten Contents

Microstructure and mechanical properties of 9Cr-W-0.06Ta Reduced Activation Ferritic-Martensitic (RAFM) steels having various tungsten contents ranging from 1 to 2 wt pct have been investigated on subjecting the steels to isothermal heat treatments for 5 minutes at temperatures ranging from 973 K to 1473 K (700 °C to 1200 °C) (below Ac₁ to above Ac₃) followed by oil quenching and tempering at 1033 K (760 °C) for 60 minutes. The steels possessed tempered martensite structure at all the heat-treated conditions. Prior-austenitic grain size of the steels was found to decrease on heating in the intercritical temperature range (between Ac₁ and Ac₃) and at temperatures just above the Ac₃ followed by increase at higher heating temperatures. All the steels suffered significant reduction in hardness, tensile, and creep strength on heating in the intercritical temperature range, and the reduction was less for steel having higher tungsten content. Strength of the steels increased on heating above Ac₃ and was higher for higher tungsten content. Transmission Electron Microscopy (TEM) investigations of the steels revealed coarsening of martensitic substructure and precipitates on heating in the intercritical temperature range, and the coarsening was relatively less for higher tungsten content steel, resulting in less reduction in tensile and creep strength on intercritical heating. Tensile and creep strengths of the steels at different microstructural conditions have been rationalized based on the estimated inter-barrier spacing to dislocation motion. The study revealed the uniqueness of inter-barrier spacing to dislocation motion in determining the strength of tempered martensitic steels subjected to different heat treatments.