Enhancement of wear and corrosion resistance of cast A356 aluminium alloy using friction stir processing

The present work pertains to investigation carried out on the feasibility of locally modifying the surface properties of cast aluminium alloy A356 using friction stir processing (FSP). The friction stir processed zone was characterized by metallography, electron micro probe analysis, hardness, dry sliding wear and potentio dynamic polarization testing. Hardness mapping showed that stir zones experienced increase of 40% compared to the as-cast metal. Further uniform micro-hardness was observed in the friction stir processed zone, which was not the case with as-cast A356 aluminum alloy. The FSP of cast A356 alloy exhibited excellent wear resistance, which is attributed to break-up of the coarse silicon rich eutectic particles, dendrite structure and homogenous distribution of fine Si particulates throughout the α-Al matrix due to intense plastic deformation and mixing during friction stir processing. The friction stir processed zone was also found to have adequate corrosion resistance. This work demonstrates that friction stir processing is an effective strategy for enhancement of wear and pitting corrosion resistance of as cast aluminum alloys     

Friction Stir Processing of Aerospace Aluminum Alloy by Addition of Carbon Nano Tube

Aluminum 7075 is an aerospace alloy that has high strength to weight ratio and used most commonly in aeronautic structures. However, low surface properties such as poor wear resistance and surface hardness are the main weaknesses that limit its application in other areas of manufacturing. In the present work an attempt was made to fabricate aluminum based surface nano-composite reinforced with carbon nano tube (CNT) by means of single pass friction stir processing. Firstly, Microstructural evolution, tensile properties, hardness, wear rate and friction coefficient of fabricated surface composite was compared with pure friction stir processed metal and base material. Hereafter, parametric study based on response surface methodology was carried out to find the effect of tool rotary speed, feed rate and amount of MWCNT on tensile strength and wear rate. Optimization based on desirability approach function was also performed to find optimal parameter setting achieving maximum strength and minimum wear rate, simultaneously. The results revealed that the CNT particles significantly homogenized the microstructure of the composite, enhanced tensile properties and hardness and reduced the wear rate and friction coefficient in sliding test. By performing optimization through RSM, it was found that selection of 1250 RPM tool rotary speed, 40 mm/min feed rate and 0.6 g CNT weight caused 20% improvement in tensile strength and wear rate of fabricated composite when compared with base material.     

Multipass Friction-Stir Processing and its Effect on Mechanical Properties of Aluminum Alloy 5086

Twelve-pass friction stir processing (FSP), with 50?pct overlap was carried out on aluminum alloy 5086-O rolled plates to obtain total area of 40?×?150?mm². Two methods of friction-stir processing, intermittent multipass friction stir processing (IMP), and continuous multipass stir processing (CMP) were carried out, and their effect on the mechanical properties of the processed material was studied. The results revealed that material subjected to IMP showed better mechanical properties compared with the material subjected to CMP. Also, a variation in mechanical properties was observed with an increase in the tool traverse speed for single-pass, CMP, and IMP types of processing.     

Friction Stir Processing for Enhancement of Wear Resistance of ZM21 Magnesium Alloy

Present work pertains to surface modification of the magnesium alloy using friction stir processing (FSP). Silicon carbide and boron carbide powders are used in the friction stir processing of the ZM21 Magnesium alloy. Coating was formed by FSP of the alloy by placing the carbide powders into the holes made on the surface. Surface coating was characterized by metallography, hardness and pin-on-disc testing. Friction stir processed coating exhibited excellent wear resistance and is attributed to grain boundary pinning and dispersion hardening caused by carbide particles. Surface composite coating with boron carbide was found to possess better wear resistance than coating made with silicon carbide. This may be attributed to formation of very hard layer coating of boron carbide reinforced composite on the surface of magnesium alloy. In the present work an attempt has also been made to compare the wear behaviour of surface composite layer on ZM21 Mg alloy with that of conventionally used engineering materials such as mild steel and austenitic stainless steel. Wear data clearly shows that wear resistance of friction stir processed composite layer is better than that of mild steel and stainless steel. This work demonstrates that friction stir processing is an effective strategy for enhancement of wear resistance of magnesium alloys.     

Effect of Cryotreatment on Tool Wear Behaviour of Bohler K390 and AISI H13 Tool Steel During Friction Stir Welding of Copper

Tool wear behaviour of powder metallurgically (P/M) produced Bohler K390 tool steel and the AISI H13 wrought tool steel before and after cryotreatment were compared by actual weight loss measurements. 3?mm thick pure copper plate was friction stir welded at a constant rotation speed of 1,200?rpm and at transverse speeds of 50,100?mm/min. It was found that the P/M tool has better wear resistance compared to the wrought alloy because of the uniform distribution of the carbides and low thermal conductivity. Cryotreatment increased the wear resistance of both the tools due to the conversion of retained austenite to martensite and formation of fine eta carbide particles.     

Sliding Wear Characteristics of Friction Stir Processed CAST ZK60 Magnesium Alloy Under Different Applied Loads

Wear resistance and poor friction are the two main draw backs of magnesium alloys that restricts structural applications. Therefore it is essential to enhance the tribological properties of magnesium alloys with the help of surface engineering without causing significant antagonistic effects on the properties of the base metal. Friction stir processing (FSP) is one of the promising thermo-mechanical processing techniques that alters the micro-structural and tribological properties of the material with low production at less period of time. Hence, this investigation enable us to study an effect of friction stir processing on wear characteristics of cast ZK60 magnesium alloy. A pin-on-disc wear testing machine was used to evaluate the wear resistance of surface modified ZK60 magnesium alloy. The result shows that the surface modification by FSP resulted in 26% increase in hardness compared to parent metal. The formation of finer grains and subsequent increase in hardness are the main reasons to improve wear resistance of FSPed ZK60 magnesium alloy.     

Friction Stir Surface Processing of Al 6061 Alloy: Role of Surface Alloying with Copper and Heat-Treatment

The current paper focuses on enhancing the surface hardness of the heat-treatable Al-alloy using the combined approach of thermal-spray, friction stir surface processing (FSSP) and heat-treatment. Copper powder was thermal-sprayed in the surface groove of Al 6061 alloy specimens followed by FSSP. Defect-free stirred zone was observed at lower transverse speed of 10 mm/min. The width of the hardness profiles across the stirred zone was increased with increase in the rotational speed of the tool. Grain refining was observed in the stirred zone due to the FSSP. In post-FSSP T6 heat-treatment, aging kinetics in the non-surface-alloyed specimen was accelerated due to the FSSP. Precipitation of Al₂Cu phase was observed in the stirred zone. Copper-alloying and post-FSSP heat-treatment were effective in enhancing the surface hardness (about 39% improvement in the surface hardness was observed).     

搅拌摩擦加工IF钢的组织性能

对3 mm厚的DC04冷轧IF钢板进行搅拌摩擦加工,研究加工区域的微观组织与力学性能.在旋转速度为950 r·min^-1,加工速度为60 mm·min^-1时,采用加工后强制冷却技术可获得光滑平整且没有缺陷的加工表面.搅拌摩擦加工后组织显著细化,加工中心的平均显微硬度约为HV 135.6,是母材硬度的1.4倍,表面细晶层硬度最高可达到HV 312.8,细晶层和过渡层的抗拉强度分别比母材的抗拉强度提高50.9%和47.6%,加工前后试样的拉伸断口均呈微孔聚合韧性断裂特征.细晶强化对材料抗拉强度的提高起主要作用.     

Microstructure,Tensile and Impact Toughness Properties of Friction Stir Welded Mild Steel

 Microstructure, tensile and impact toughness properties and fracture location of friction stir welded AISI 1018 mild steel are revealed in this paper. The 5 mm thick AISI 1018 mild steel plates were friction stir welded with tool rotational speed of 1000 rpm and welding speed of 50 mm/min with tungsten base alloy tool. Tensile strength of stir zone is higher (8%) when compared to the base metal. This may be due to the formation of finer grains in the weld nugget region under the stirring action of the rotating tool. The ductility and impact toughness of the joints are decreased compared to the base metal and this is due to the inclusion of tungsten particles in the weld region.     

Microstructure and Wear Behavior of Zircon Reinforced Copper Based Surface Composite Synthesized by Friction Stir Processing Route

Although copper has its use in many industrial and functional applications, but its low wear resistance limits its potential application. Hard particulates are generally reinforced in bulk copper to increase its wear resistance but it tend to decrease its toughness. Thus the present research focuses on synthesis of copper based surface composite by friction stir processing. Zircon sand was used as reinforcement in copper as it is hard and fairly inexpensive. To prepare the composites, a groove of defined dimension was machined in the copper plate for compaction of zircon sand (18 vol%) at the centre of the plate. After filling the zircon sand in grooves, friction stir processing technique was employed to reinforce it in copper. For microstructure analysis, XRD, microhardness and wear characterization, specimens were cut from the processed portion of the plate. The micrograph obtained by optical and scanning electron microscope revealed equiaxed and fine grain structure in stir zone with no sign of concentration gradient, aggregation and segregation of particles. XRD pattern revealed no peaks corresponding to intermetallics or interfacial reaction products. The microhardness and wear resistance of fabricated surface composite improved significantly as compared to pure copper. The micrograph of worn surface was also analysed to investigate the predominant wear mechanisms. Adhesion and delamination wear were predominant wear mechanisms in pure copper whereas these wear mechanism was not significant in Cu/Zircon composite.     

Taguchi Optimisation of Friction Stir Processing Parameters to Achieve Maximum Tensile Strength of Mg AZ31B Alloy

In this investigation, the effect of friction stir processing process variables such as rotational speed, traverse speed and tool tilt angle on the tensile strength of magnesium alloy AZ31B was studied. The experiments were carried out according to the Taguchi parametric design L9 at various combinations of process parameters and statistical optimization technique ANOVA was used to determine the optimum levels and to find the percentage of contribution of the process parameters. The results indicate that the rotational speed is the most significant factor followed by the traverse speed and tool tilt angle for maximising the tensile strength of the friction stir processed magnesium alloy.     

Modelling Corrosion Behavior of Friction Stir Processed Aluminium Alloy 5083 Using Polynomial: Radial Basis Function

Aluminium alloy 5083, widely used in marine applications, undergoes accelerated corrosion in sea water due to the aggressive reaction of chloride ions with the secondary phase particles and other intermetallics present in the alloy matrix. The corrosion rate of the alloy is also influenced by the temperature difference between the alloy and its environment. Friction stir processing (FSP) is a recent solid state processing technique for improving the surface properties of metals and alloys. In this study, an attempt has been made to explore the possibility of improving the corrosion resistance of AA5083 by FSP. FSP trials were performed by varying the tool rotation speed, tool traverse speed and shoulder diameter of the tool, as per face centered central composite design. The corrosion potential and the corrosion rate of friction stir processed AA5083 was studied using potentiodynamic polarization studies, at three different temperatures. Mathematical models based on polynomial—radial basis function were developed and used to study the effect of process parameters on the corrosion potential and the corrosion rate of friction stir processed AA5083. FSP resulted in refinement of the grain structure, dispersion and partial dissolution of secondary phase particles in the matrix, which increased the corrosion resistance of the alloy.     

Transformation and Deformation Texture Study in Friction Stir Processed API X80 Pipeline Steel

The nature of deformation in friction stir welding/processing (FSW/P) is complex which is further complicated when allotropic phase transformations are present. Electron backscattered diffraction (EBSD) is used as a means to reconstruct prior austenite texture and grain structure to study deformation and recrystallization in austenite and ferrite in FSW/P of high strength low alloy (HSLA) steels. Analyses show evidence of shear deformation textures such as A1* (111)[?1?12], B (1?12)[110], and ?B (?11?2)[?1?10], as well as rotated-cube recrystallization texture in the reconstructed prior austenite. Existence of rotated-cube texture as well as polygonal grain structure of the prior austenite implies that recrystallization is partially occurring in elevated temperatures. Room temperature ferrite exhibits well-defined shear deformation texture components. The observed shear deformation texture in the room temperature microstructure implies that FSW/P imposes deformation during the phase transformation. The evolution of both elevated and room temperature textures in friction stir processed API X80 steel are presented.     

Application of Taguchi Method on Biaxial Stretch Forming of Friction Stir Processed Mg AZ31B Alloy

The present study describes the effect of friction stir processing parameters on formability of Mg AZ31B sheet under biaxial stretching. The formability of friction stir processed sheet was studied by limiting dome height test in biaxial strain deformation mode. The experiments were carried out as per the Taguchi parametric design concepts and an L9 orthogonal array was used to study the influence of various combinations of process parameters. Statistical optimization technique, ANOVA was used to determine the optimum levels and to find the significance of each process parameter. The results indicate that the traverse speed is the most significant factor followed by the rotational speed and the tilt angle in deciding the formability of friction stir processed magnesium alloy. In addition, mathematical model was developed to establish relationship between the different process variables with formability by regression analysis.     

铁粉类型对铜基粉末冶金摩擦材料性能的影响

采用粉末冶金工艺分别制备含还原铁粉、泡沫纤维铁粉和铁合金粉的铜基摩擦材料,研究了铁粉种类对摩擦材料摩擦磨损性能的影响.当摩擦转速从3000 r·min^-1提升至6200 r·min^-1,用还原铁粉制备的样品,其摩擦因数随速度的升高出现严重衰退;含泡沫纤维铁粉的样品具有稳定的摩擦因数,试验范围内其波动值不超过0.024,但是磨损严重;采用铁镍合金粉制备的样品可有效减缓高速阶段摩擦因数的衰退,高速下摩擦因数波动低于0.027.以铁铬合金粉制备的样品,其磨耗随摩擦速度的增加几乎不发生变化,抗磨损能力最佳.     

Microstructure and Wear Performance of ECAP Processed Cast Al–Zn–Mg Alloys

In the present investigation, wear performance of equal channel angular pressing (ECAP) processed cast Al–Zn–Mg alloys under dry sliding wear conditions was studied against a steel disc. Initially, Al–Zn–Mg alloys (with 5, 10, 15% zinc and 2% magnesium) were ECAP processed. After ECAP, grain size was reduced and enhancement in the hardness was observed. Wear resistance of the alloys increased after ECAP processing. Wear resistance of the alloys also increased when the quantity of the zinc was increased in the alloys. But, wear resistance of all three alloys decreased with increase in the load and the sliding speed. Coefficient of friction of the alloys decreased after ECAP processing. Coefficient of friction of the alloys also decreased when the quantity of the zinc was increased in the alloys. Coefficient of friction of all three alloys increased with increase in the load and the sliding speed. Irrespective of the alloy composition and applied load, worn surfaces of the cast and homogenized samples were composed of plastic deformation, scratches and micro-ploughing. On the other hand, in ECAP processed samples, morphology of the worn surfaces depended on the applied load. Abrasive wear is the main wear mechanism perceived in cast and homogenized samples at all loads. While in ECAP processed samples, the wear mechanism shifted from adhesive and oxidation wear to abrasive wear with increase in the load. Formation of oxide layers on the surface of the sample increased with increase in the ECAP passes. In ECAP processed samples, transfer of iron content from the disc to the sample surface was identified.     

Study on the friction and wear properties of the surface nanocrystallized 1.0C-1.5Cr steel induced by the surface mechanical attrition treatment

Nano-structured layers are fabricated on the surface of 1.0C-1.5Cr steel by using the surface mechanical attrition treatment(SMAT)technology,and the microstructures of the surface nano-crystallization layers are characterized by means of X-ray diffraction(XRD)and transmission electron microscopy(TEM).The friction and wear properties are also investigated by a UMT-2 friction and wear tester.Experimental research has indicated that the average diameter of nanocrystalline grains in the surface layer after being treated for 15 min is in the range of 10-20 nm,and ferrite and cementite grains can not be identified by their morphologies.The wear-resistance of the specimen treated for 15 min has been doubled,compared with that of the matrix due to the grain refinement to a nano-sized scale.The lowest friction coefficient is 0.27,which is for the specimen treated for 30 min,resulting from the dissolution of the cementite phase and the formation of a relative homogenous structure.The SMAT technique for enhancing the wear-resistance of the 1.0C-1.5Cr steel has an optimum processing time,which is in the range of 15-30 min.The dominant wear mechanism of the specimen treated for 15 min changes from adhesive wear into particle wear.     

Influence of Texture on Mechanical Behavior of Friction-Stir-Processed Magnesium Alloy

Friction stir processing (FSP) improves the mechanical properties of metallic materials. In this study, a magnesium alloy AZ31B was friction stir processed by using single and multiple pass. The friction-stir-processed magnesium alloy exhibits higher tensile strength and ductility in the transverse direction (TD) compared to the longitudinal direction (LD). Both single pass and multiple (two) pass friction-stir-processed material show similar anisotropy in tensile properties, but the multiple pass friction-stir-processed material shows fine-grained microstructure with higher tensile strength and ductility. The tensile anisotropy in the friction-stir-processed AZ31B originated from the textured microstructure that evolved during FSP.     

Some Observations on Microstructural Changes in a Mg-Based AE42 Alloy Subjected to Friction Stir Processing

The main aim of the current study is the analysis of friction stir processing (FSP) of Mg-based alloys as a possible tool for nanocomposites production. The study reports microstructural changes taking place in a Mg-based alloy (AE42) subjected to FSP under different cooling conditions. The FSP process was carried out with single as well as multipass options. The friction stir processed samples were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), focused ion beam (FIB)-scanning ion microscopy (SIM), and X-ray diffraction (XRD). It was observed that FSP tends to fragment the elongated precipitates and produces near homogeneous distribution of fine particles. The smallest particle size was observed to be produced by double-pass FSP supplemented by rapid cooling, thereby generating in situ nanocomposites. Vickers microhardness testing was done along the thickness (transverse direction) of the specimen to study and understand the variation of hardness with thickness. Nearly a two-times increase in the microhardness of AE42 was observed in the case of double-pass, FSP AE42 with cooling at temperature of approximately 253 K (–20 °C). To confirm these observations, another magnesium alloy AM50 was also friction stir processed under similar conditions. The fine submicron grain structure produced in AE42 alloy contributed immensely toward grain boundary strengthening and Orowan strengthening had only marginal influence. Subgrain boundary pinning by in situ nanoparticles contributed significantly in the strengthening process.     

Facilitating Basal Slip to Increase Deformation Ability in Mg-Mn-Ce Alloy by Textural Reconstruction Using Friction Stir Processing

The widespread application of wrought magnesium alloys is hampered by their insufficient formability at room temperature. The tensile ductility of a newly developed Mg-Mn-Ce alloy has been dramatically improved by friction stir processing (FSP). The microstructure of the stir zone was characterized mainly by elongated fine grains which were highly separated by low-angle grain boundaries because of the high contribution of continuous dynamic recrystallization. A new {0002} distribution with high basal plane tilt angles which facilitated 〈a〉 basal slip when the specimens were pulled along the FSP direction was obtained. Both the enhanced basal slip and crystallographic orientation evolution of Mg crystals increased the strain hardening exponent of the FSP specimen, and hence improved its tensile ductility. A material flow model, developed based on the local textural evolution, could reasonably explain the phenomenon that the FSP specimen exhibited warping and a high normal anisotropy ratio during tensile test.