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.     

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.     

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.     

搅拌摩擦加工法制备碳纳米管增强铝基复合材料

为了制备晶粒细小、 组织均匀的复合材料, 提高材料的力学性能, 用搅拌摩擦加工法制备碳纳米管增强铝基复合材料, 并对不同碳纳米管含量的复合材料的微观结构、 拉伸性能及断口形貌进行分析。结果表明: 碳纳米管添加到铝基体中, 搅拌摩擦中心区晶粒细小, 碳纳米管与基体之间结合良好, 未发现明显的缺陷; 碳纳米管对基材有明显的强化作用, 铝基复合材料抗拉强度随着碳纳米管含量的增加而提高; 碳纳米管体积分数为7%时, 抗拉强度达到201 MPa, 是基材的2.2倍; 复合材料在宏观上呈现脆性断裂特征, 微观上呈现韧性断裂特征, 其断裂机制以CNTs/Al界面脱粘、 基体撕裂和增强体断裂为主。      

Effect of friction stir processing and hybrid reinforcements on copper

In this research, a copper based surface composite was fabricated through dispersing hybrid composite particles onto its surface through friction stir processing (FSP) technique. Optical micrographs and scanning electron microscopy images indicates finer refinement of grains and particles dispersion into matrix along with its bonding and particle separation. As per the outcomes of microhardness analysis, hardness of the developed surface composite shows increment with increase in dispersion of volume fraction of hybrid particles. Strength of the developed copper surface composite exhibited a positive trend with introduction of hybrid reinforcement particle onto the surface of the composite but yet again ductility reduced. Wear resistance of the composite increased with reinforcement addition and the same was supported through worn out surface morphology. Fluctuations in friction coefficient value reduced with increase in particles, as for the presence in BN particles while the average frictional coefficient value was observed increasing. A reduction in corrosion rate was observed with increase in reinforcement particle dispersion onto copper matrix through FSP.     

Investigation of friction stir processing effect on AA 2014-T6

This study is concerned with the effects of process parameters such as speed, feed, tilt angle, and tool profile on mechanical and microstructural properties of stir processed, solution treated, and artificially aged AA 2014-T6. The process was carried out with an input condition at rotational and traverse feeds of 600–1400 RPM and 30–90 mm/min, respectively. Five distinct shapes of the tool pin such as triangular, hexagonal, threaded, conical, and cylindrical have been selected to carry out the process with varied tilt angle of 1°–3°. In order to exemplify the status of processed materials, optical, scanning electron microscopy and Vickers hardness measurement along with grain analysis were performed on various regions of processed cross sections. According to the results, combination of processing speed and rotational speed affects the microstructure and associated grain size and average hardness of the processed region.     

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.     

Joining of metal matrix composites using friction stir welding: a review

The application of fusion welding process is restricted to certain grades of alloys and materials. Solid-state joining process offers greater advantages over fusion welding process such as fumeless and effective joining, minimum or no preparation time, environment friendly, etc. One such solid-state joining process is friction stir welding (FSW), which uses a non-consumable rotating tool. This rotating tool joins the two faying surfaces of the workpiece by forging them. This joining technique successfully joins metals, alloys and metal matrix composite (MMC), which are considered as difficult to join using conventional processes. The present study is an endeavor to review a specific domain of FSW, i.e. joining of MMCs. The initial part of the study provides a detailed introduction about the FSW process, and along with it, an overview of the published literature related to FSW of alloys has been presented. The later part of the study pays specific attention to macrostructure, microstructure, joint properties and residual stresses in welded joints along with wearing of tool during welding of MMC. The observations of this study provide a basis for future research in the specified domain.     

搅拌摩擦加工制备羟基磷灰石增强镁复合材料的微观组织和力学性能

通过搅拌摩擦加工（Friction stir processing,FSP）制备了羟基磷灰石增强镁（HA/WE43）复合材料,研究了主轴转速对HA分布的影响及FSP加工前后材料微观组织和力学性能的变化。使用光学显微镜、SEM、TEM对该复合材料的显微组织进行了表征,同时对其显微硬度和室温拉伸性能进行了测试。结果表明:制得的HA/WE43复合材料晶粒尺寸相比于母材发生了显著的细化,加工过程中,HA颗粒的存在增强了FSP的晶粒细化作用;主轴转速较低时,HA/WE43复合材料中的HA团聚较严重,随着主轴转速的增加,HA的分布更加均匀,团聚现象得到改善;尽管局部团聚的HA颗粒会成为复合材料在拉伸变形过程中的裂纹源,但HA/WE43复合材料的极限抗拉强度、屈服强度和伸长率相对于母材仍有明显提高。      

Critical Assessment 25: Friction stir processing,potential and problems

This assessment considers recent work on friction stir processing (FSP), which has been demonstrated to be an effective method for grain refinement and synthesis of new alloys and composites. The grain refinement is attributed to high strain rates leading to recrystallisation, while external cooling suppresses grain growth during cooling. The technique is capable of producing nanocrystalline alloys, and also able to disperse nanoparticles into alloys. The mechanical properties of processed materials agree with a combination of existing models for grain refinement, and precipitate reinforcement theory. Further improvements in the technique may help deal with severe tool wear during the FSP of composites, and reduce the complexity of composite fabrication using novel processing methods and tooling.     

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.     

Corrosion study and quantitative measurement of crystallite size of high strength aluminum hybrid composite developed via friction stir processing

This present study is centered on the corrosion behaviors and structural integrity of high strength aluminum-alloy 7075-T651 hybridized with carbonaceous coconut shell ash (CSA) and α+β titanium alloy powder in ratio of 50 : 50, fabricated during friction stir processing (FSP). The study examined the base metal – AA7075-T651 as well as the friction stir processed AA7075-T651 as control experiments. The Processing parameters used were plunge depth of 0.3 mm, travel speed of 20 mm/min, the tilt angle of 3° and rotational speed of 1500 min⁻¹. The corrosion characteristics were examined with the Potentiodynamic Polarization method in 3.5 % NaCl medium while crystalline phases were studied with x-ray diffraction (XRD). Results show that fabricated aluminum hybrid composite (AHC) AA7075-T651/coconut shell ash (CSA)/titanium-alloy has the highest percentage of inhibition performance efficiency (IPE) of 84.81 % resulting to 0.76938 mm/year corrosion rate and 356.51 Ω polarization resistance, whereas inhibition performance efficiency (IPE) for friction stir processed (FSPed) AA7075-T651 was 63.99 % while the base metal – AA7075-T651 was taken as the reference point. It was also revealed that the hybridized coconut shell ash (CSA)/titanium-alloy powder on AA7075-T651 enhanced the structural integrity, producing 38.5 nm crystallite size over friction stir processing (FSP) AA7075-T651 with 41.2 nm and the base metal with 48.7 nm crystallite size.     

Laser bending of friction stir processed and cement-coated sheets

In this work, laser bending of friction stir processed and cement-coated sheets of aluminum alloy and mild steel was carried out using CO₂ laser. For comparison, the laser bending of uncoated raw sheets was also carried out. It was noted that friction stir processing roughened the surface and helped in getting larger bend angle due to increased absorptivity in laser bending. However, the cement-coated sheets provided much larger bend angles. The micro-hardness of friction stir processed sheets was larger compared with unprocessed sheets and it further increased after laser bending. After laser bending, the micro-hardness increased from bottom surface to irradiated top surface. It was always more than the micro-hardness of the raw sheet. A study of microstructures revealed that the grain size reduced after laser bending and increased from top irradiated surface to bottom surface.     

Effect of processing parameters on static strength of dissimilar friction stir spot welds between different aluminium alloys

The effect of processing parameters on static strength and fracture mechanisms of dissimilar friction stir spot welds between different aluminium alloys was studied. Tensile shear strength increased with decreasing tool rotational speed and increasing tool holding time, while cross tension strength decreased with increasing both parameters. Two fracture modes were observed: nugget shear fracture and mixed mode fracture under tensile shear loading, and debonding and pull‐out of the nugget under cross tension loading. Based on experimental observation, the dependence of static strength on processing parameters and the occurrence of different fracture modes were discussed.     

用强冷摩擦搅拌工艺制备超细晶紫铜板材

提出了一种制备整块、全板厚超细晶板材的强冷摩擦搅拌工艺，利用搅拌头与基材之间摩擦搅拌过程的剧烈塑性变形条件细化金属晶粒，通过搅拌位置的机械移动制备整块的超细晶板材．同时，采用强制冷却方式抑制动态回复和再结晶晶粒的长大，提高晶粒细化效果．建立了该工艺过程中应变速率、应变量及加热功率的数学模型，优化了紫铜板材细晶制备工艺参数，对所制得的细晶材料进行了硬度试验和显徽组织分析．结果表明，增强冷却能减小晶粒尺寸和提高细晶材料的硬度．制备出的超细晶紫铜板材布氏硬度可达HBS100，比退火紫铜的硬度约高一倍．     

铝/镀锌钢搅拌摩擦铆焊接头组织与力学性能

为实现铝钢之间的优质连接,采用搅拌摩擦铆焊新方法对6061铝合金和DP600镀锌钢进行搭接点焊,利用扫描电子显微镜、能谱仪及拉伸试验对接头的微观组织及力学性能进行了研究.结果表明:接头成形平整美观,中心没有匙孔;接头包含铆接区和扩散区,其中在铆接区铝合金以铝柱的形式嵌入到钢板的圆孔中,形成了一个"铝铆钉",底部有富铝的α固溶体偏聚,圆孔四周形成扩散区,铝和钢形成了冶金结合,依靠金属间化合物Fe Al3连接在一起;接头有3种断裂形式,在最佳工艺参数下接头的抗剪力达到8.2 k N;铝柱上断口的微观形貌是被拉长的韧窝,扩散区的断口由灰色基体和白色颗粒组成.     

镁合金搅拌摩擦焊接工艺参数优化

为了优化镁合金搅拌摩擦焊接工艺参数,对5 mm厚镁合金AZ31B板材的搅拌摩擦焊接技术进行了试验研究,利用SN比实验设计,对镁合金AZ31B搅拌摩擦焊接工艺参数进行了方差分析,优化了搅拌头的材料、结构,最终确定搅拌头的材料为W6Mo5Cr4V2,结构为凹面圆台形.轴肩尺寸为12 mm.探针的根部直径为5.5 mm,端部直径为2.5 mm,长度为4.7 mm.获得镁合金AZ31B搅拌摩擦焊的工艺参数显著性顺序为旋转速度、横向速度和压力;确定了镁合金AZ31B搅拌摩擦焊的最优工艺参数为1500 r/min、47.5 mm/min、3kN.     

Producing nanostructured super-austenitic steels by friction stir processing

In the present work, friction stir processing (FSP) was used to produce the nanostructured super-austenitic steel. After preheating, the specimens were subjected to FSP using the rotation and traverse speed of 2600 rpm and 30 mm min⁻¹, respectively. The specimen temperature during FSP was about 950 ± 2 °C. The results show that a nanostructured layer of about 91 μm thick was produced on the specimen surface. The formed nanograins ranged from 50 to 90 nm. Besides, the hot severe deformation applied during FSP led to significant fragmentation of the coarse sigma particles to nanosize ones.The produced nanostructured layer was then characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The formed nanostructure led to a twofold increase in the hardness. The formation of nanostructure resulted in an increase in hardness up to 350 Hv, comparing to 185 Hv pertaining to base structure of super austenitic steel.     

{10-12} twinning induced texture randomisation of friction stir processed AZ31B Mg alloy

Friction stir processing (FSP) with additional liquid nitrogen cooling was conducted on hot-rolled AZ31B Mg alloy. The FSP can simultaneously provide compress deformation perpendicular to the c-axis and tensile deformation parallel to the c-axis of close-packed hexagonal crystal cell. Massive {10-12} twins were activated under the two deformation modes, resulting in significantly reduced basal texture intensity. All six {10-12} twin variants were activated in the stir zone according to the Schmid factor criterion, and they provide a great contribution to basal texture randomisation. This study also provides a simple and effective method to remarkably reduce the basal texture intensity for deformed Mg alloy.     

Stationary shoulder tool in friction stir processing: a novel low heat input tooling system for magnesium alloy

Present work aims to propose a new and novel low heat input stationary shoulder friction stir processing (SSFSP) for grain refinement. It uses stationary shoulder and rotating probe tool, which generates low heat input and small temperature gradient across thickness of material. In this study, SSFSP was performed in 6.35 mm thick AZ31B magnesium alloy without use of external cooling. The homogenous grain refinement occurred throughout the thickness (top, middle, and bottom). Enhancement in hardness and ductility exhibited minimum anisotropy across the processing thickness. Furthermore, fractography confirmed the similar fracture modes with dimples and tear ridges in all tensile specimens across the thickness.