Challenges in dissimilar friction stir welding of aluminum 5052 and 304 stainless steel alloys

In this study, dissimilar friction stir welding of aluminum 5052 and stainless steel 304 has been carried out with different process parameters. This investigation provides a better insight regarding the defect formation of the weld joints with tilt angles ranging from 0 ° to 2.5 °. The experiments were conducted according to Taguchi L9 orthogonal array by changing the tool rotational speed, and welding speed. The tool pin was kept 70 % towards the aluminum with the tool rotational speed ranging from 800 min⁻¹ to 1200 min⁻¹ with a varying traverse speed of 5 mm/min to 15 mm/min. The bottom part of the stir zone was perfectly welded without any defects. Tunnel defect was detected just above the bottom welded surface. Microstructural analysis reveals that the weld between both materials is formed on the retreating side, whereas on the advancing side, the weld was formed with void defects. Mostly, the stir zone is filled with irregular shaped aluminum and steel parts which were detached from the base material. Several other defects such as voids, cracks, and fragmental defects were observed in the stir zone irrespective of the process parameters. It was observed from the experimental investigations that the tunnel defect can be reduced by increasing the tilt angle.     

Investigation of microstructure and mechanical properties of nano MgO reinforced Al composites manufactured by stir casting and powder metallurgy methods: A comparative study

In the present work, Al–nano MgO composites using A356 aluminum alloy and MgO nanoparticles (1.5, 2.5, and 5 vol.%) have been fabricated via stir casting and powder metallurgy (PM) methods. Different processing temperatures of 800, 850, and 950 °C for stir casting and 575, 600, and 625 °C for powder metallurgy were considered. Powder metallurgy samples showed more porosity portions compare to the casting samples which results in higher density values of casting composites (close to the theoretical density) compare to the sintering samples. Introduction of MgO nanoparticles to the Al matrix caused increasing of the hardness values which was more considerable in casting samples. The highest hardness value for casting and sintering samples have been obtained at 850 and 625 °C respectively, in 5 vol.% of MgO. Compressive strength values of casting composites were higher than sintered samples which were majorly due to the more homogeneity of Al matrix, less porosity portions, and better wettability of MgO nanoparticles in casting method. The highest compressive strength values for casting and sintered composites have been obtained at 850 and 625 °C, respectively. Scanning electron microscopy images showed higher porosity portions in sintered composites and more agglomeration and aggregation of MgO nanoparticles in casting samples which was due to the fundamental difference of two methods. Generally, the optimum processing temperatures to achieve better mechanical properties were 625 and 850 °C for powder metallurgy and stir-casting, respectively. Moreover, casting method represented more homogeneous data and higher values of mechanical properties compare to the powder metallurgy method.     

Synergetic lubricating effect of MoS2 and Ti3SiC2 on tribological properties of NiAl matrix self-lubricating composites over a wide temperature range

NiAl matrix self-lubricating composites with MoS₂ and Ti₃SiC₂ lubricants were prepared by spark plasma sintering. The tribological behaviors of the NiAl–Ti₃SiC₂–MoS₂ composites against Si₃N₄ were investigated from room temperature to 800 °C. The results showed that the composites exhibited excellent self-lubricating and anti-wear properties over a wide temperature range. At 400 °C, the composites containing 5Ti₃SiC₂–5MoS₂ (wt.%) had a very low friction coefficient of about 0.13 and a low wear rate of 4.5 × 10⁻⁵ mm³ N⁻¹ m⁻¹. MoS₂ played the main role of lubrication at low temperatures, while Ti₃SiC₂ was responsible for low friction at high temperatures. Ti₃SiC₂ and MoS₂ lubricants in the NiAl–Ti₃SiC₂–MoS₂ composites showed the excellent synergetic lubricating effect over a wide temperature range from room temperature to 800 °C.     

Potentiality of artificially aged aluminium 6061 hybrid composites reinforced with granite and graphite micro–fillers for structural applications

The current study explores the feasibility of artificial aging treatment to aluminium alloy 6061 hybrid composites reinforced with graphite and fine granite particulates to suit structural applications. Aging at 100 °C retrieved a better response of the hybrid composites as compared to that at 150 °C in terms of peak hardness and strength. Among the five different stir‐cast compositions, the composition of aluminium 6061 with 2 wt. % graphite and 4 wt. % granite showed enhanced mechanical properties than that of the base alloy as well as mono reinforcement type composites which was attribued to the formation of rod‐shaped β‐Mg₂Si precipitates.     

Different reinforcement strategies of hybrid surface composite AA6061/(B4C+MoS2) produced by friction stir processing

Aluminum surface composites have gained huge importance in material processing due to their noble tribological characteristics. The reinforcement of solid lubricant particles with hard ceramics further enriches the tribological characteristics of surface composites. In the current study, friction stir processing was chosen to synthesize hybrid surface composites of aluminum containing B₄C and MoS₂ particles with anticipated improved tribological behavior. B₄C and MoS₂ powder particles in 87.5: 12.5 ratio were reinforced into the AA6061 by hole and groove method. Microstructural observations indicated that reinforcement particles are well distributed in the matrix. The hardness and wear resistance of hybrid surface composites improved as compared to the base material, due to well distributed abrasive B₄C and solid lubricant MoS₂ particles in AA6061. The hybrid surface composites achieved ∼32 % increased average hardness as compared to the base material. Hole method revealed ∼13 % better wear resistance compared to the groove method for friction stir processed hybrid surface composite, attributing to an improved homogeneity of particle distribution shown by zigzag hole pattern. Moreover, friction stir processed AA6061 without reinforcement particles exhibited reduced hardness and wear resistance due to loss of strengthening precipitates during multi-pass friction stir processing.     

Flexural behaviour of CNT-filled glass/epoxy composites in an in-situ environment emphasizing temperature variation

The paucity of structural defects in carbon nanotube (CNT) with unrivalled mechanical properties has always posed an interest to material scientists for its potential incorporation in soft polymer resins to achieve superior mechanical stability. Present investigation focuses on the assessment of flexural behaviour of glass/epoxy (GE) and multiwalled carbon nanotubes (MWCNT) embedded glass/epoxy (0.3 wt. % of epoxy) (CNT-GE) composites at different in-service environmental temperatures. In-situ 3-point bend tests were performed on GE and CNT-GE composites at −80 °C, −40 °C, room temperature (20 °C), 70 °C and 110 °C temperatures at 1 mm/min crosshead speed. The results revealed that at 110 °C temperature, the flexural strength of GE and CNT-GE composites was significantly decreased by 67% and 81% respectively in comparison to their strength at −80 °C temperature. Similarly, 38% and 77% decrement in modulus was noted for GE and CNT-GE composites respectively. Dynamic mechanical thermal analysis (DMTA) was carried out in the temperature range of −100 °C to 200 °C to correlate the mechanical and thermo-mechanical response of both the material systems. Addition of 0.3 wt. % MWCNT in GE composite resulted in lowering of glass transition temperature (T_g) by 12 °C. Furthermore, to understand various possible deformation and failure mechanisms, the post failure analysis of the fractured specimens, tested at different temperatures, was carried out using scanning electron microscope (SEM). The critical parameters needed during designing composite structures were calculated and modelled using Weibull constitutive model.     

Effect of pre‐processing annealing and ram speed on mechanical properties for low carbon steel processed by constrained groove pressing

Constrained groove pressing (CGP) has emerged for producing ultra‐fine‐grained materials with distinguished properties. Low carbon steel sheets were subjected to severe plastic deformation by constrained groove pressing process. The effect of pre‐processing annealing temperature, ram speed and number of passes on microstructure, mechanical properties and wear behaviour of the sheets were investigated. The 3 mm thick sheets were deformed by a constrained groove pressing die at ram speeds: 5 mm/min, 10 mm min^?1 and 20 mm min^?1. Furthermore, the as received sheets were annealed at 600 °C and 900 °C, then deformed at ram speed 20 mm min^?1. The annealing temperature 900 °C led to slightly coarser grains, lower strength and larger ductility compared to those obtained after annealing at 600 °C. With lowering the ram speed to 5 mm min^?1, the number of passes could be increased to 10 passes while increasing ram speed from 5 mm min^?1 to 20 mm min^?1 improved the mechanical properties; after 3 constrained groove pressing passes, the ultimate tensile strength increased from 420 MPa to 490 MPa, the hardness from 174 HV 1 to 190 HV 1 and the elongation from 7.6 % to 9.5 %. Finer grains were also obtained by increasing ram speed. Wear resistance was greatly enhanced by constrained groove pressing and by the increase in ram speed.     

The effect of tool rotational and traverse speed on friction stir weldability of AISI 430 ferritic stainless steels

In this study, the effects of tool rotational speed and traverse speed on welding of AISI 430 (X6Cr17, material number 1.4016) ferritic stainless steels by friction stir welding method are examined. Two specimens with dimension of 3 × 100 × 200 mm were joined in butt position. Tool rotational speeds were determined to be 560–1400 min⁻¹ and traverse speeds as 80–200 mm/min. During the studies, tool pressure force 3.5 kN and tool angle of 0° was kept constant. Hard metal carbide (WC-Co hard metal identified as K10) with equilateral triangle tip profile was used as the tool material. Determination of the tool advance speeds related to the tool rotation speeds giving the best-looking weld seals with acceptable values of mechanical properties was aimed.During welding of the specimens joined in butt position, the temperature change due to time and variation of the pressure force applied on welded specimens by the tool shoulder has been recorded. It has been observed that the best mechanical resistance values were obtained at tool rotational speed of 1120 min⁻¹ through five tool rotational speeds (560–1400). Also it has been observed that the best mechanical resistance values were obtained at traverse speed of 125 mm/min through five traverse speeds (80–200) with the constant tool pressure force of 3.5 kN and tool angle of 0°.     

On the role of matrix grain size and particulate reinforcement on the hardness of powder metallurgy Al–Mg–Si/MoSi2 composites

Six Al–Mg–Si composites reinforced with 15 vol.% of MoSi₂ intermetallic particles, together with three unreinforced monolith Al–Mg–Si (AA6061) alloys have been processed by powder metallurgy to quantify the roles of alloy matrix grain size and reinforcement particle on their solutionized hardness and ageing response. In the range studied, hardness of solutionized composites follows a Hall–Petch mechanism. Moreover, it can be rationalised as the sum of the hardness of the alloy matrix with the same matrix grain size (d) and a term H_R, that accounts for 17–27% of total hardness, is roughly constant and independent of reinforcing size and distribution. Matrix grain size is responsible for 50–65% of hardness, whereas the contributions of solid solution and Orowan strengthenings account for 17–26%. Upon heat treatment at 170 °C, hardening ability decreases linearly with d^?1/2, fitting all data points to a single equation independently of whether they correspond to the composites or to the monolith alloys.     

Preparation of carbon thin films from five-membered heterocyclic organic compounds by chemical vapor deposition

Thin carbon films were prepared from five-membered heterocyclic organic compounds [tetrahydrofuran (THF), borane-THF (B-THF), pyrrolidine (PYL), 1-3 dimethyl-2-imidazolidinone (DMI), cyclopentane (CP)] by chemical vapor deposition (CVD). The vapor generated by heating the compound was carried by flowing Ar and decomposed on a silica glass substrate to deposit carbon films at 750 to 1000 °C. The films were studied by scanning electron microscopy (SEM), X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Their growth rates were determined as a function of temperature (750 to 1000 °C) and Ar flow rate (5 to 35 ml min⁻¹). The presence of pyridine- and pyrrole-type nitrogen was confirmed in the PYL- and DMI-derived carbon films. The electrical conductivity of films prepared at 800 and 900/1000 °C was of the order of 10³ and 10⁴ S m⁻¹, respectively. The micro-Vicker's hardness of films prepared at 800 °C was 2.2–3.6 GPa, becoming greater (3.3–5.2 GPa) at 1000 °C.     

Attainment of high specific hardness and specific modulus in spark plasma sintered aluminium-copper-silicon carbide-titanium carbide hybrid composite

Aluminium matrix hybrid composites have been consolidated effectively by spark plasma sintering with new combinations of reinforcement and high volume percentage of ceramic particulates to maximize specific hardness and specific modulus through the powder metallurgy route. The aforementioned techno-scientific accomplishment with regard to metal matrix composite aims to meet a continuous increase in the global demand for a material with minimum structural weight and high-modulus for structural (automotive and aerospace) applications. The new aluminium based hybrid composite developed by incorporating ceramic particulate reinforcements (12.5 wt.% silicon carbide and 12.5 wt.% titanium carbide) along with 22.5 wt.% copper as the metallic reinforcement attains significantly high specific hardness (85 HV/gcm⁻³), specific Young's modulus (33.56 GPa/g cm⁻³), specific bulk modulus (27.97 GPa/g cm⁻³) when compared with the reported range of specific hardness (13 HV/g cm⁻³–89 HV/g cm⁻³), specific Young's modulus (24 GPa/g cm⁻³–27 GPa/g cm⁻³) and specific bulk modulus (20 GPa/g cm⁻³–22 GPa/g cm⁻³) possessed by structural steels. This is accredited to the genesis of a novel microstructure that consists of fine copper, silicon carbide and titanium carbide particulates together with a nominal in-situ originated aluminium-copper equilibrium phases distributed in a highly substructured aluminium based matrix with a significant dislocation density (7.56 ⋅ 10¹⁴ m^-2).     

Influence of reinforcing particles on microstructure and mechanical properties of friction stir processed aluminium alloy AA7075-T651

This paper emphasis the improvement of mechanical properties of AA7075-T651 using friction stir processing through localized surface modification by adding nano boron carbide particles. The reinforcement techniques such as the groove and blind hole methods were used by changing reinforcements of nano boron carbide and a matrix of AA7075-T651 surface composites volume percentages (2 %, 4 %, and 6 %) along with tool rotational speed and processing speeds. Optical microscopy, scanning electron microscope and x-ray diffraction analysis were used to examine the particle dispersion for the surface composites and to correlate with the enhanced mechanical properties. Results revealed that high input parameters have given grain coarsening and precipitate agglomeration and low input parameters provide poor nugget metal consolidation and no vertical material flow. The L9 orthogonal Array designed and optimized the process parameters for enhancing the surface properties of processed samples. Mechanical properties like ultimate tensile strength, yield strength, hardness, percentage of elongation and impact strength were evaluated for the groove friction stir processing method and blind-hole friction stir processing methods. From the results, it has been observed that the blind-hole technique resulted in higher hardness and the homogenous dispersion of nano boron carbide particles in the stir zone than the groove method. Consequently, for blind-hole friction stir processing, grey relational analysis (GRA) and particle swarm optimization (PSO) approaches were proposed to optimise process parameters. From the compared optimization results between grey relational analysis and particle swarm optimization, particle swarm optimization approach was shown the best optimization results. Successively, the optimum condition in the respective experimentation is accomplished. Based on these observation and results, final validation tests were carried by changing the volume percentages of reinforcement keeping tool rotation speed and tool processing speed as constant. It is apparent that dynamic recrystallization in aluminium alloy at the processed zone due to presence of heterogeneous nucleation sites with nano boron carbide particles.     

Physico‐mechanical characterization of garnet and fly ash reinforced Al7075 hybrid composite

The aim of present work was to study the effect of adding garnet and fly ash on the physical and mechanical performance of Al7075 hybrid composites. Al7075 hybrid composites reinforced with varying weight percentage (0 wt.%–15 wt.%) of each of garnet and fly ash were fabricated and characterized for the comparative assessment of their physical and mechanical properties. The physical and mechanical tests such as void content test, hardness test, tensile strength test, impact strength tests, flexural and fracture toughness test were performed for both garnet and fly ash reinforced composites. The finding of results indicated that the addition of 0 wt.%–15 wt.% of garnet increased the void content, hardness, flexural strength, tensile strength, impact strength and fracture toughness in the range of 1.01 %–2.69 %, 33 HRB–88 HRB, 165 MPa–275 MPa, 205 MPa–263 MPa, 12 J–22 J and 0.11 MPa ? m^1/2–0.58 MPa ? m^1/2 at crack length 0.1 respectively whereas addition of 0 wt.%–15 wt.% of fly ash increased the void content, hardness test, flexural strength, tensile strength, impact strength and fracture toughness in the range of 1.010 %–1.351 %, 33 HRB‐80 HRB, 165 MPa–225 MPa, 205 MPa–236 MPa, 12 J–20 J, 0.11 MPa ? m^1/2–0.48 MPa ? m^1/2 at crack length 0.1 respectively. Apart from the economic concern and void issue, Garnet indicated better choice of reinforcement as compared to fly ash in terms of mechanical properties.     

The thermal expansion and mechanical properties of high reinforcement content SiCp/Al composites fabricated by squeeze casting technology

With mixing different sized SiC particles, high reinforcement content SiCp/Al composites (V_p=50, 60 and 70%) for electronic packaging applications were fabricated by squeeze casting technology. The composites were free of porosity and SiC particles distributed uniformly in the composite. The mean linear coefficients of thermal expansion (20–100 °C) of SiCp/Al composites ranged from 8.3 to 10.8×10⁻⁶/°C and decreased with an increase in volume fraction of SiC content. The experimental coefficients of thermal expansion agreed well with predicted values based on Kerner's model. The Brinell hardness increased from 188.6 to 258.0, and the modulus increased from 148 to 204 GPa for the corresponding composites. The bending strengths were larger than 370 MPa, but no obvious trend between bending strength and SiC content was observed.     

Effects of Al-Ni powder addition on dissimilar friction stir welding between AA7075-T6 and 304 L

Friction stir welding between AA7075-T6 aluminum alloy and 304 L stainless steel sheet metal was performed with the addition of Al−Ni powder between the joining interfaces to increase the joining performance. The welding tool was rotated at 200 min⁻¹ to 800 min⁻¹ with the constant traverse speed of 25 mm/min. The resulting joint interfaces were analyzed using a field emission-scanning electron microscope and energy-dispersive x-ray spectroscopy analysis. The tensile strength was greater for the Al−Ni powder added specimens at the lower tool rotational speeds. The tensile strength of 360 MPa was obtained for the ‘with-powder’ specimen as compared to 220 MPa for the ‘without-powder’ specimen at the 200 min⁻¹ tool speed. Electron microscope images of the stir zone showed a significant mixing of the Al−Ni powder with the base materials, increased contact at the interface, which resulted in increased joining strength at the lower tool rotational speeds. However, based on the images, intermetallic compound that may contribute to the joining strength in the vicinity of the interfacial region was not detected.     

Effects of copper addition on the in-situ synthesis of SiC particles in Al–Si–C–Cu system

In this research work, SiC particles have been successfully in-situ synthesized in Al–Si–Cu matrix alloy utilizing a novel liquid–solid reaction method. The effect of copper addition on the synthesis of SiC in Al–Si–C–Cu system was investigated. The composites mainly contain spherical SiC particles and θ-Al₂Cu eutectic phases, which are embedded in the α-Al matrix. Results indicated that the temperature for forming in-situ SiC particles significantly reduced from 750 °C to 700 °C with the copper addition. The size of in-situ synthesized SiC particles can be as low as 0.2 μm. Further study found that the addition of 10 wt.% copper into Al–Si–C alloy causes its solidus temperature to decrease by about 65 °C. Additionally, the Rockwell hardness value of SiCp/Al–18Si–5Cu composites has an average of 92, which is 50% higher than that of the sample without copper addition.     

Statistical optimization of hydrate formation conditions of TBAB and THF mixture as a cold storage material for air-conditioning system based on response surface methodology

Response surface methodology has been employed to optimize the hydrate formation conditions of tetra-n-butylammonium bromide (TBAB) and tetrahydrofuran (THF) mixtures as cold storage materials for air-conditioning system. It has been focused on the maximization of sub-cooling driving force and electrical conductivity variations of hydrate formation considering the operating conditions. The results of ANOVA have revealed that TBAB/THF mass ratio has significant effect on sub-cooling driving force, while stirrer speed and jacket temperature are significant factors for electrical conductivity variations. According to RSM, the optimum TBAB/THF mass ratio, stirrer speed and jacket temperature have been respectively found to be 1.96, 784 rpm and −6.66 °C for sub-cooling driving force and 1.23, 798 rpm and −5.2 °C for electrical conductivity variations of hydrate formation. Overall desirability function of both responses has provided one optimal condition yielding TBAB/THF mass ratio of 1.47, stirrer speed of 800 rpm and jacket temperature of −6.4 °C.     

Effect of copper content on the thermal conductivity and thermal expansion of Al–Cu/diamond composites

Al–Cu matrix composites reinforced with diamond particles (Al–Cu/diamond composites) have been produced by a squeeze casting method. Cu content added to Al matrix was varied from 0 to 3.0 wt.% to detect the effect on thermal conductivity and thermal expansion behavior of the resultant Al–Cu/diamond composites. The measured thermal conductivity for the Al–Cu/diamond composites increased from 210 to 330 W/m/K with increasing Cu content from 0 to 3.0 wt.%. Accordingly, the coefficient of thermal expansion (CTE) was tailored from 13 × 10⁻⁶ to 6 × 10⁻⁶/K, which is compatible with the CTE of semiconductors in electronic packaging applications. The enhanced thermal conductivity and reduced coefficient of thermal expansion were ascribed to strong interface bonding in the Al–Cu/diamond composites. Cu addition has lowered the melting point and resulted in the formation of Al₂Cu phase in Al matrix. This is the underlying mechanism responsible for the strengthening of Al–Cu/diamond interface. The results show that Cu alloying is an effective approach to promoting interface bonding between Al and diamond.     

Experimental investigation on mechanical properties and wear characterization of Al-Si12CulMg1 aluminium alloy reinforced with titanium diboride and boron carbide particulate hybrid composites using stir casting process

LM13 aluminium alloy (Al−Si12CulMg1) with titanium diboride (TiB₂) and boron carbide (B₄C) particulate hybrid composites have been prepared using stir casting process. Wt% of titanium diboride is varied from 0–10 and constant 5 wt% boron carbide particles have been used to reinforce LM13 aluminium alloy. Microstructure of the composites has been investigated and mechanical properties viz., hardness, the tensile strength of composites have been analyzed. Wear behavior of samples has been tested using a pin on disc apparatus under varying load (20 N–50 N) for a sliding distance of 2000 m. Fracture and wear on the surface of samples have been investigated. Microstructures of composites show uniform dispersion of particles in LM13 aluminium alloy. Hardness and tensile strength of composites increased with increasing wt % of reinforcements. Dry sliding wear test results reveal that weight loss of composites increased with increasing load and sliding distance. Fracture on the surface of composites reveals that the initiation of crack is at the interface of the matrix and reinforcement whereas dimples are observed for LM13 aluminium alloy. Worn surface of composites shows fine grooves and delamination is observed for the matrix.     

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al₄C₃ and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl₂O₄ in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution.