Investigating effects of process parameters on microstructural and mechanical properties of Al5052/SiC metal matrix composite fabricated via friction stir processing

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite (MMC) was fabricated on surface of 5052 aluminum sheets by means of 5 μm and 50 nm SiC particles. Influence of tool rotational speed, traverse speed, number of FSP passes, shift of rotational direction between passes and particle size was studied on distribution of SiC particles in metal matrix, microstructure, microhardness and wear properties of specimens. Optimum of tool rotational and traverse speed for achieving desired powder dispersion in MMC was found. Results show that change of tool rotational direction between FSP passes, increase in number of passes and decrease of SiC particles size enhance hardness and wear properties.     

Microstructure and microhardness of AA1050/TiC surface composite fabricated using friction stir processing

Friction stir processing (FSP) has been developed by several researchers to produce an upper surface modification of metallic materials. The fabrication of TiC particulate (~2? $\upmu $ m) reinforced aluminum matrix composite (AMC) using FSP is studied in this paper. The measured content of TiC powders were compacted into a groove of 0.5?mm × 5.5?mm. A single pass FSP was carried out using a tool rotational speed of 1600?rpm, processing speed of 60?mm/min and axial force of 10?kN. A tool made of HCHCr steel, oil hardened to 62 HRC, having a cylindrical profile was used in this study. The microstructure and microhardness of the fabricated AMC were analysed. Scanning Electron Microscope (SEM) micrographs revealed a uniform distribution of TiC particles which were well-bonded to the matrix alloy. The hardness of the AMC increased by 45% higher than that of the matrix alloy.     

Microstructural evaluation and corrosion properties of aluminium matrix surface composite adding Al-based amorphous fabricated by friction stir processing

A novel aluminium matrix surface composite adding Al_84.2Ni₁₀La_2.1 amorphous, which the layer depth was 5 mm, was fabricated by friction stir processing. The surface composite region shows obvious sandwich structure. The average hardness of the surface composite is about HV97, higher than the base metal is about HV80. The maximum tensile strength of the processed aluminium plate with the surface composite is 410 MPa. The surface composite was mainly composed of phases α-Al, Mg₂Al₃, MnAl₆ and La₃Al₁₁. The surface composite added the amorphous strip had the lower icorr, corrosion current density, and the higher passivation current than the surface composite not added amorphous strip. And there is obvious passivation zone for the surface composite. However, a large number of ultrafine grained which was composed of the α-Al and α-Al amorphous structures can be observed in the surface composite. And the grain size range of them is 90–400 nm. It is conceivable that the existence of these ultrafine grained structures and change of crystal plane would contribute greatly to improve the mechanical properties and corrosion resistance of the aluminium matrix surface composite.     

Prediction of mechanical and wear properties of copper surface composites fabricated using friction stir processing

Friction stir processing (FSP) has evolved as a novel solid state method to prepare surface composites. In this work, FSP technique has been successfully applied to prepare copper surface composites reinforced with variety of ceramic particles such as SiC, TiC, B₄C, WC and Al₂O₃. Empirical relationships are developed to predict the effect of FSP parameters on the properties of copper surface composites such as the area of the surface composite, microhardness and wear rate. A central composite rotatable design consisting of four factors and five levels is used to minimize the number of experiments. The factors considered are tool rotational speed, traverse speed, groove width and type of ceramic particle. The effect of those factors on the properties of copper surface composites is analyzed using the developed empirical relationships and explained in this paper taking into account the microstructural characterization of the prepared copper surface composites. B₄C reinforced composites have higher microhardness and lower wear rate.     

Particulate metal matrix composites and their fabrication via friction stir processing – a review

Particulate-reinforced metal matrix composites are of particular interest because of their ease of fabrication, low cost, and isotropic properties. Friction stir processing offers a promising alternative in the fabrication of surface as well as bulk metal matrix composites. Its very nature aids in the microstructural refinement of the matrix material, avoids the formation of detrimental phases and provides flexible control of the process. Over the period, the technique was successfully applied in the synthesis of various composites. This paper conducts a critical review of the current trends and strategies used to enhance friction stir process efficiency during fabrication of particulate metal matrix composites. It discusses a few of the key underlying principles necessary for making the right combination of matrix and reinforcement. The exhaustive comparative study presented in this article helps in identifying matrix/reinforcement combinations that are yet to be addressed. In the end, a few crucial observations are summarized and important suggestions are provided for future work.     

Analysis of first mode metal transfer in A413 cast aluminum alloy during friction stir processing

Friction stir processing (FSP) is a recent processing technique where a non consumable rotating cylindrical tool is used to generate frictional heat and local plastic deformation at selected processing locations. In cast alloys, FSP eliminates casting defects and refines micro structures, and leads to improvement in their mechanical properties. The metal flow phenomenon in friction stir processing (FSP) comprises two modes of metal transfer. The first mode of metal transfer takes place layer by layer and is caused by the shearing action of the tool shoulder, while the second mode is caused by the extrusion of the plasticized metal around the pin. The aim of the present study is to quantitatively determine the amount of metal transferred by the first mode during friction stir processing of cast aluminum A413 alloys and its influence on the tensile properties. The experimental results show that the mechanical properties can be enhanced through FSP and the enhanced properties have good correlation with the first mode of metal transfer.     

Fabrication of 5052Al/Al2O3 nanoceramic particle reinforced composite via friction stir processing route

In this research, microstructure and mechanical properties of 5052Al/Al₂O₃ surface composite fabricated by friction stir processing (FSP) and effect of different FSP pass on these properties were investigated. Two series of samples with and without powder were friction stir processed by one to four passes. Tensile test was used to evaluate mechanical properties of the composites and FSP zones. Also, microstructural observations were carried out using optical and scanning electron microscopes. Results showed that grain size of the stir zone decreased with increasing of FSP pass and the composite fabricated by four passes had submicron mean grain size. Also, increase in the FSP pass caused uniform distribution of Al₂O₃ particles in the matrix and fabrication of nano-composite after four passes with mean cluster size of 70 nm. Tensile test results indicated that tensile and yield strengths were higher and elongation was lower for composites fabricated by three and four passes in comparison to the friction stir processed materials produced without powder in the similar conditions and all FSP samples had higher elongation than base metal. In the best conditions, tensile strength and elongation of base material improved to 118% and 165% in composite fabricated by four passes respectively.     

Issues and strategies in composite fabrication via friction stir processing: A review

Friction stir processing (FSP) is an expeditiously emerging novel technique involving exterior layer modification, which enables one to successfully fabricate surface composites (SCs) as well as bulk composites of the metal matrix. SCs constitute an exclusive class of composites which exhibit improved surface properties while retaining the bulk properties unaltered. During initiative years, FSP was employed in development of SCs of light metal alloys like aluminum. But, nowadays, it has gained a shining role in the field of SC fabrication of various nonferrous alloys like aluminum, magnesium, copper, and even ferrous metals like steel etc. This article reviews the current trends, various issues, and strategies used to enhance the efficiency of the fabrication process of SCs. Factors involved in the process of SC fabrication are discussed and classified with a new approach. Also, variation of microstructural and mechanical characteristics with these factors is reviewed. In addition to a brief presentation on the interaction between various inputs and their effects on properties, a summary of literature on SC fabrication for different metals is tabulated with prominent results. Subsequently, shortfalls and future perspectives of FSP on SC fabrication domain are discussed.     

Distribution of reinforcement particles in surface composite fabrication via friction stir processing: Suitable strategy

Fabrication of metal matrix surface composites (SCs) is an emerging trend of friction stir processing applications. Key factors affecting the properties of SCs are process parameters, tool geometry, tool dimensions and reinforcement strategies. In this research, effects of different reinforcement strategies and varying tool offset positions on dispersion of reinforcement particles in the base matrix are investigated. The experiments were performed in two phases using AA6063 as base metal at constant process parameters of 1120?rpm rotational speed, 40?mm/min traverse speed and 2.5° tilt angle. In the first phase, effect of six different reinforcement strategies on the reinforcement particles distribution and defect formation was studied. It was found that groove method with tool offset in retreating side (RS) exhibited better homogeneity in reinforcement distribution out of the six reinforcement strategies considered. In the second phase, effect of variation of tool offset in RS was investigated. Results from second phase of experimentation reflected that the best dispersion of reinforcement powder with larger stir zone area was found with 1.5?mm tool offset which is numerically half of the tool pin radius. The results were supported by macro and microstructural images obtained from the optical microscope and scanning electron microscope.     

Fullerene/A5083 composites fabricated by material flow during friction stir processing

Fullerene was successfully dispersed into A5083 by friction stir processing (FSP). Dispersion of the fullerene enhanced the grain refinement by recrystallization during the FSP and the grain size reached ∼200 nm. The hardness was also remarkably increased by both the grain refinement and the dispersion of the fullerene molecules.In this study, material flow during the FSP was investigated with respect to the dispersion of the fullerene. It was revealed that the formation mechanism of the “onion ring” was closely related to the convectional flow induced by the shoulder of the rotating tool. This material flow by the shoulder is very important when fabricating the surface composites by the FSP in order to provide a uniform dispersion of the reinforcement.     

Particle-reinforced aluminum matrix composites produced from powder mixtures via friction stir processing

Particle-reinforced aluminum matrix composites were produced from powder mixtures of aluminum and silicon by using multiple passages of friction stir processing (FSP). In the composites, the Si particles with an average size of ∼1.5 μm are uniformly dispersed in the aluminum matrix which has a fine-grained structure (∼2 μm). The strengthening mechanism of the composites is discussed. It indicates that the fine grain size of aluminum, the Orowan strengthening due to intragranular particles and the dislocations generated by thermal mismatch all contribute significantly to the composite yield strength.     

Barium titanate reinforced nickel aluminium bronze surface composite by friction stir processing

Friction stir processing (FSP) is a surface modification technique, which can be used for the fabrication of surface composites. In the present work, a surface composite was prepared by introducing a piezoelectric ceramic powder (PZT; BaTiO₃) to a nickel aluminium bronze (NAB) metal matrix using FSP. BaTiO₃ powder was placed in holes drilled at the centre of a NAB plate and FSP was carried out. Microstructural characterisation of the surface composite was carried out using optical microscopy and scanning electron microscopy. The microhardness and tensile behaviour of the surface composite were investigated, together with the cavitation erosion behaviour. The results are discussed in light of the microstructural modification.     

搅拌摩擦加工制备MWCNTs／Al复合材料显微结构及硬度

采用搅拌摩擦加工技术（FSP）制备多壁碳纳米管增强铝基（MWCNTs／A1）复合材料,并对该复合材料的显微结构和硬度进行分析。结果表明：MWCNTs／Al复合材料显微结构为细小的等轴晶,晶粒大小不均匀;MWCNTs与Al基体界面结合良好,界面处分布大量的位错,MWCNTs主要分布在晶内;动态再结晶形核方式为亚晶形核,在...     

Microstructure and mechanical properties of friction stir welded Al/Mg2Si metal matrix cast composite

In this research, friction stir weldability of 15 wt.% Mg₂Si particulate aluminum matrix cast composite and effects of tool rotation speed and number of welding passes on microstructure and mechanical properties of the joints were investigated. Microstructural observations were carried out by employing optical and scanning electron microscopy of the cross sections perpendicular to the tool traverse direction. Mechanical properties including microhardness and tensile strength were evaluated in detail. The results showed fragmentation of Mg₂Si particles and Mg₂Si needles existing in eutectic structure in stir zone. Also, homogeneous distribution of Mg₂Si particles was observed in the stir zone as a result of stirring with high plastic strains. Tension test results indicated that tensile strength of the joint had an optimum at 1120 rpm tool rotation speed and decreased with increasing of the number of welding passes. Hardness of the joint increased due to modification of solidification microstructure of the base composite. This research indicates that friction stir welding is a good candidate for joining of 15 wt.% Mg₂Si aluminum matrix composite castings.     

Microstructure and mechanical property of multi-walled carbon nanotubes reinforced aluminum matrix composites fabricated by friction stir processing

Aluminum matrix composites reinforced by different contents of multi-walled carbon nanotubes (MWCNTs) were fabricated by friction stir processing (FSP). The microstructure of nano-composites and the interface between aluminum matrix and MWCNTs were examined using optical microscopy (OM) and transmission electron microscopy (TEM). It was indicated that MWCNTs were well dispersed in the aluminum matrix throughout the FSP. Tensile tests and microhardness measurement showed that, with the increase of MWCNT content, the tensile strength and microhardness of MWCNTs/Al composites gradually increased, but on the contrary, the elongation decreased. The maximum ultimate tensile strength reached up to 190.2 MPa when 6 vol.% MWCNTs were added, and this value was two times more of that of aluminum matrix. Appearances and fracture surface micrographs of failed composite samples indicated that the composites become more and more brittle with the increase of the MWCNT content.     

Influence of friction stir processing parameters on surface modified 90Cu-10Ni composites

Friction Stir Processing (FSP) has emerged as a distinctive and pioneering solid state technique to produce surface composites. The objective of the present research is to produce reinforced 90/10 Copper–Nickel surface composites with different carbide-based ceramic particles through FSP and study the relationship of its dynamic parameters including tool rotational speed, tool traverse speed, and width of the groove over the surface behavior. Responses such as sliding wear, microhardness, and surface modified area in the friction stir processed region are modeled using polynomial, nonlinear, multiple regression based on the central composite design of experiment. Analysis of the developed models showed that the FSP parameters; traverse speed, rotational speed, and groove width have significant influence on both the sliding wear and microhardness of developed surface composite. And furthermore, tool rotational speed and tool traverse speed, simultaneously control dispersion of reinforcement in the surface. To validate the abovementioned noteworthy results and to study the microstructural aspects, selected specimens were carried over metallurgical analysis and the obtained results were put forward in detail in this paper.     

添加La_2O_3对搅拌摩擦加工制备Ni/Al复合材料组织和性能的影响

采用搅拌摩擦加工(FSP)方法在Al基体中添加微米级Ni粉及(Ni+La_2O_3)混合粉末,制备Ni/Al及(Ni+La_2O_3)/Al复合材料。采用SEM、EDS及XRD对复合区微观结构及相组成进行分析,采用室温拉伸试验对Ni/Al、(Ni+La_2O_3)/Al复合材料力学性能进行了测试。结果表明:Ni/Al复合材料中主要成分为Al、Al3Ni和Ni粉团聚物,Ni粉团聚物尺寸粗大,形貌呈壳-核结构,核为团聚的Ni,壳为Al3Ni增强相层;La_2O_3对Al-Ni原位反应有较大影响,能够强化Al-Ni原位反应,生成更多增强相;La_2O_3阻碍了Ni粉的相互吸附和聚拢行为,从而减少了团聚现象;(Ni+La_2O_3)/Al复合材料的抗拉强度可以达到186 MPa,与Al基体(抗拉强度72 MPa)、纯Al FSP(抗拉强度90 MPa)、Ni/Al复合材料(抗拉强度144 MPa)相比,其抗拉强度分别提高了158%、107%、29%。     

Strengthening mechanisms of aluminum matrix composite containing Cu-coated SiC particles produced by friction stir processing

ABSTRACT

A friction stir processing (FSP) method has been developed to fabricate a locally reinforced aluminum matrix composite (AMC) by stirring electroless-copper-coated SiC particles into AA6061 matrix. The interfacial bonding between particulate reinforcement and the matrix was enhanced by the copper coating. Effective improvement in hardness and in tensile strengths has been proved. Microstructural investigation and analyses were conducted to correlate the microstructural evidences with the possible strengthening mechanisms. The effect of copper coating on the bonding between SiC particles and Al-matrix; the role of the dispersed Cu debris and the increased Cu content in solid solution on the strengthening; and the effect of friction stir on dislocation density and on the recrystallization behavior were analyzed. Multiple strengthening mechanisms due to diffusion between copper film and matrix; dispersion of fine copper debris and Al-Cu intermetallic compounds (IMCs) in the matrix; solid solution due to increased copper content and dislocation punching were four major mechanisms in interpreting the strengthening phenomena in AMC containing copper coated SiC reinforcements.     

Optimization of cold-sprayed AA2024/Al2O3 metal matrix composites via friction stir processing: Effect of rotation speeds

In this study, friction stir processing (FSP) was employed to modify cold-sprayed (CSed) AA2024/Al₂O₃ metal matrix composites (MMCs). Three different rotation speeds with a constant traverse speed were used for FSP. Microstructural analysis of the FSPed specimens reveals significant Al₂O₃ particle refinement and improved particle distribution over the as-sprayed deposits. After FSP, a microstructural and mechanical gradient MMC through the thickness direction was obtained. Therefore, a hybrid technique combining these two solid-state processes, i.e. CS and FSP, was proposed to produce functionally gradient deposits. The Guinier-Preston-Bagaryatskii zone was dissolved during FSP, while the amounts at different rotation speeds were approximately the same, which is possibly due to the excellent thermal conductivity of the used Cu substrate. Mechanical property tests confirm that FSP can effectively improve the tensile performance and Vickers hardness of CSed AA2024/Al₂O₃ MMCs. The properties can be further enhanced with a larger rotation speed with a maximum increase of 25.9% in ultimate tensile strength and 27.4% in elongation at 1500 rpm. Friction tests show that FSP decreases the wear resistance of CSed MMCs deposits due to the breakup of Al₂O₃ particles. The average values and fluctuations of friction coefficients at different rotation speeds vary significantly.     

Study of friction stir welded A319 and A413 aluminum casting alloys

Cast aluminum alloys A319 and A413 were friction stir welded using a rotating steel screw tool. The cast microstructures were characterized by numerous inclusions or second phase particles which were homogeneously stirred into the weld zone. TEM analysis illustrated the dynamic recrystallization which facilitates the solid-state flow, and digital microhardness measurements through the base metals and the weld zones illustrate the absence of any property degradation. In fact the comminution of particles in the weld zone decreased the interparticle spacing and increased the corresponding hardness by 15%.