Microhardness Survey Research Articles

Metallurgical and mechanical investigation on FSSWed dissimilar aluminum alloy

The present work is the novel examination of influence of welding process parameters and material flow on the mechanical and microstructural characteristics during the FSSW of dissimilar AA2024/AA7075 joint were evaluated and compared with similar AA2024/AA2024 and similar AA7075/AA7075 FSSW joints. The microstructural and physical properties of two aluminum alloy joined through friction stir spot welding (FSSW) were examined. The aluminum alloys namely AA2024-T3 and AA7075-T6 were selected for the investigation owing to their typical and potential applications in aeronautical industry. The input parameters were tool rotational speed, plunge depth and dwell time (TRS 1800 rpm, 3.3 mm plunge depth and 45 s dwell time) were utilized. The microstructure of the welded specimen was investigated by scanning electron microscope and their chemical compositions were analyzed by energy-dispersive X-ray spectroscopy. The physical properties were investigated by Vickers microhardness survey and the specimen strength evaluated by tensile tests. The experimental investigation revealed the influence of the tool pin penetration and frictional heat on the microstructure, distribution of the grain structure affecting the microhardness and the tensile properties of the dissimilar joint.

Microstructure, tensile properties and fracture toughness of friction stir welded AA7075-T651 aluminium alloy joints

Abstract The main objective of this investigation is to study the microstructure, tensile properties and fracture toughness of friction stir welded (FSW) butt joints of 10 mm thick AA7075-T651 plates. The microstructural features of stir zone (SZ), thermos-mechanically affected zone (TMAZ), heat affected zone (HAZ) were analyzed using optical microscopy technique. The tensile properties were evaluated using smooth and notch tensile specimens and compared to base metal properties. The microhardness survey was done across the weld cross section and correlated to the failure of tensile specimens. Compact tension (CT) specimens were used to evaluate the fracture toughness of welded joints. The fractured tensile and CT specimens were analyzed using scanning electron microscopy (SEM). Results showed that the FSW AA7075-T651 specimens welded using axial load of 12 kN, tool rotation speed of 750 rpm and welding speed of 30 mm/min exhibited 412 MPa tensile strength and 9% elongation. It showed 88 and 89% of base metal strength elongation. The joints showed fracture toughness of 23 MPa m1/2 which is 80% of base metal fracture toughness. The superior tensile and fracture toughness properties of joints are mainly attributed to the evolution of finer grains in SZ due to the stirring action of FSW tool.

Effect of Holding Time on Bonding Strength and Joint Interface Microstructure of Vacuum Diffusion Bonded Dissimilar Austenitic Stainless Steel - Titanium Alloy Joints

In this investigation, the effect of holding time on the microstructure of joint interface and bonding strength of vacuum diffusion bonded dissimilar austenitic stainless (ASS) – titanium (Ti) alloy joints were investigated. The dissimilar joints of ASS - Ti alloy were developed using the holding time of 30, 45, 60, 75 and 90 minutes in a vacuum chamber at a temperature of 900⁰C and pressure of 14 MPa. The bonding strength of ASS – Ti alloy joints was evaluated using the ram tensile test. The microhardness survey was done perpendicular to the joint interface. The microstructure of the joint interface was analyzed using optical microscopy (OM). The evolution of intermetallic compounds at the joint interface was analyzed using X-ray diffraction (XRD). The microstructure of the joint interface was correlated to the bonding strength of joints.

Waste to wealth: Recycling of steel slag as flux for the submerged arc welding process and its effect on mechanical and metallurgical properties of welds

A novel technology has been developed to recycle steel slag as a flux for the submerged arc welding process. The chemical, mechanical, and metallurgical properties of welds produced using recycled slag have been evaluated and compared with that of fresh flux available in the market. The tensile strengths of weld metal prepared with recycled slag and fresh flux are 462.25 MPa and 471.49 MPa, which are comparable. The impact strength of welds produced using recycled slag is 83.66 J which is acceptable in accordance with AWS SFA 5.17 specifications. The welds produced were subjected to non-destructive tests such as radiography and also dye-penetration test apart from visual inspection to ascertain the soundness of welds produced. Metallurgical investigations were carried out, and a favorable microstructure containing acicular ferrite was obtained in welds deposited using recycled slag. Similar trends of microhardness survey have been observed in both the welds produced.

Influence of Scandium on AA5052-H32/AA5083-H111 TIG welded joint

ABSTRACT In the present work, two aluminum alloys 5052-H32 and 5083-H111 were tungsten inert gas welded using ER5356 filler and scandium added modified ER5356 filler rod. The morphologies of the weld joints were analyzed and characterized for microstructure and physical properties by optical microscopy, scanning electron microscopy, tensile testing and Vickers` microhardness survey. The scandium from the modified filler rod was found to fuse with aluminum of the base alloy plates in the weld zone and enhanced the yield strength of the joint by 46 MPa. The corresponding increase in ultimate tensile strength was observed to be 48 MPa. The improved strength rates were attributed to the formation of aluminum – scandium dispersoids that effectively restrained the recrystallization and growth of grains, greatly enhancing the weld joint performance. The resulting scandium added weld joint had excellent weld geometry while exhibiting active control over intermetallic compound within the material fusion zone. The ultimate tensile strength and microhardness of this joint were enhanced considerably.

Experimental Investigations on Joining of Equal Channel Angular Pressed Structural Steel IS2062 with Friction Welding Method

In this study, the equal channel angler pressed (ECAPed) structural steel (IS2062) samples were joined by friction welding, and mechanical properties were analysed. The single-pass ECAP process was conducted at ambient (room temperature-RT) and hot (H) condition. The as-received, H-ECAPed and RT-ECAPed samples exhibit strengths of 422 MPa, 730 MPa and 662 MPa, respectively, after welding. The fractography analysis shows a ductile mode of failure in the as-received and RT-ECAPed samples. In the H-ECAPed sample, a brittle fracture occurs in the welding interface. This result confirms that the H-ECAPed sample has a higher strength than the weldment. Microstructural analysis shows that the weldment has finer grains than the ECAPed samples. However, the microhardness survey reveals that the weldment has a lower hardness. This is due to the presence of a moderate dislocation density in the different zones, which is confirmed through the transmission electron microscope (TEM). From the overall observation, the sample which has been H-ECAPed followed by friction welding is found to exhibit better mechanical properties than the other samples.

Influence of welding parameters on the weld properties in Friction stir spot welding of aluminium alloys of varying thicknesses

Joining of dissimilar materials with different thicknesses in automobile and shipbuilding industries by conventional arc welding methods is a challenge due to unequal stress distribution during welding. The problem of imbalanced stress can be reduced or avoided in solid state welding methods. In the present work, aluminium alloys of dissimilar thickness are joined by Friction stir spot welding, FSSW. The feasible welding conditions were determined by Response surface methodology. The maximum strength of 6.204 kN was obtained at 1000 RPM, 0.02 mm/s plunge speed and thread pin profile. The rotational speed was identified as the vital parameter that influenced the joint strength by analysis of variance. The Artificial neural network was used to predict the mechanical strength of the weld joints. The microstructure analysis revealed that tool profile significantly influenced the hook shape. The microhardness survey revealed that the stir zone hardness was higher than the hardness at the heat-affected zone due to severe plastic deformation.

Conventional and underwater friction stir welded AA2024-T351 aluminium alloy – a comparative analysis

Purpose Friction stir welding (FSW) and underwater friction stir welding (UWFSW) of aluminium alloy 2024-T351 was carried out, with a chosen set of parameters, namely, rotational speed of 450 rpm, 560 rpm and 710 rpm, welding speed of 25 mm/min, 40 mm/min and 63 mm/min and tool tilt angle of 0º, 1° and 2º. This study aims to understand the correlation between temperatures and weld parameters, finite element simulation was carried out using Abaqus®. Design/methodology/approach Comparative analysis of the mechanical properties of the samples welded with FSW and UWFSW was carried out and correlated with that of the microstructures. Microhardness survey was also conducted across the weldments to support the findings. Findings Samples welded with higher rotational speed and low traverse speed favoured good quality, defect-free welds with enhanced material flow. Underwater welded samples resulted in improved mechanical properties than that of the samples welded with conventional FSW. Higher cooling rates resulted in finer grains in all UWFSW samples than that of conventional FSW samples, which, in turn, also reflected in the microhardness survey done across the weldments. Among the chosen window of the parameter, samples welded with 710 rpm, 25 mm/min and 2° had shown improvement in mechanical properties. Research limitations/implications This work was carried out in a milling machine, which limits the rotational speed which could be used. Optimistically, this limitation also paves way for using the commonly available milling to be used for FSW. Originality/value This original research study shall open opportunities to enable FSW and UWFSW to be done on similar/dissimilar joints of varying composition. Additionally, this research study throws enough light on the age – hardenable aluminium alloy being welded in a commonly available milling machine.

Effect of variants of gas metal arc welding process on tensile properties of AA6061-T6 aluminium alloy joints

This article describes the influence of gas metal arc welding (GMAW) variants on tensile properties of welded thin sheets of AA6061-T6 aluminium alloy. Single V butt joints were fabricated using the four variants of the GMAW process (constant current, pulsed current, cold metal transfer and pulsed cold metal transfer) under optimized conditions. Transverse tensile properties of the welded joints were evaluated, and a microhardness survey was done along the cross section of the joints. Higher hardness is recorded in the weld metal, i.e., 79 Hv for the pulsed cold metal transfer (PCMT) joint which is 14% higher than the continuous current GMAW joints. It is observed that a PCMT-welded joint exhibited the highest tensile strength of 227 MPa which is 16% higher than the continuous current GMAW joints. The fracture surface of the tensile specimens is highly dominated by the dimples with tearing ridges which suggests that the joints have experienced sufficient plastic deformation before failure irrespective of the welding process. The results demonstrated that the joints fabricated using the PCMT process exhibited superior tensile properties with controlled segregation of phases compared to the other variants of the GMAW process due to the pulsing effect associated with the retraction of the wire.

Interface Microstructure Characteristics of Friction-Welded Joint of Titanium to Stainless Steel with Interlayer

Dissimilar joining between stainless steel and titanium by friction welding enhances the metallurgical compatibility and properties of the interface. The severity of the formation of intermetallic compounds is inhibited up to some extent. However, the complete prevention of the Fe–Ti and Cr–Ti type of intermetallic compounds cannot occur. In this study, the interlayer technique has been applied to develop friction-welded joints between dissimilar materials. Tantalum is one of the candidate materials to act as an interlayer between titanium and stainless steel and can form ample metallurgical compatibility with both of the substrates. The interface between stainless steel and interlayer exhibited the presence of a mixed region. The diffusion of titanium atoms into the interlayer is revealed along with the interface of titanium to an interlayer. The electron probe microanalyzer characterized the diffusion of atoms at interfaces. The microhardness survey unveiled the increasing hardness over the stainless steel and interlayer interface.

Study on Hardness and Microstructural Properties of Ti-6Al-4V Alloy using Overlapped Multipass Laser Transformation Hardening under Optimized Test Conditions

In this research paper, overlapped multipass Laser Transformation Hardening (LTH) of Ti-6Al-4V titanium alloy sheet of 2 mm thickness was analyzed experimentally for uniformly intense, CW spherical beam moving with constant speed using 2 kW Nd: YAG laser. Experiments were conducted for optimized two sets of laser process parameters: 1. High Laser Process Parameter (HLPP), Lp = 800 Watts, Ss = 3000 mm/min, Fp = -10 mm, with heat input 180 J/cm and 2. Low Laser Process Parameter (LLPP), Lp = 600 Watts, Ss = 2000 mm/min, Fp = -10 mm, with heat input 160 J/cm respectively having same Fp = -10 mm. The maximum, minimum and average hardened depths of 0.27, 0.19 and 0.23 mm respectively, achieved for HLPP were found to be minimum, as compared to the maximum, minimum and average hardened depths of 0.38, 0.29 and 0.33 mm, respectively, for LLPP. Measurements of Vickers micro-hardness survey of the hardened zone of the laser processed Ti-6Al-4V alloy are presented. Vickers micro-hardness of an as-received two-phase (α+β) Ti-6Al-4V titanium alloy is 328 HV. The results showed that Vickers micro-hardness on top of the surface (TS), in hardened or fusion zone (Fz), at the interface of Fz -Haz, in the heat affected zone (Haz) is higher than the bulk material. The high hardness values of 450 HV and 445 HV were investigated on the top surface for high and low laser process parameters respectively. This can be the quality characteristics of the dissolution of small amounts of oxygen, nitrogen, and carbon with hard martensite α' (transformed β) formation, thereby ensuring an increase in wear resistance of laser treated hardened surface of Ti-6Al-4V considerably in relation to the untreated or base alloy.

Process parameter optimization and characterization of friction stir welded advancing side AA6082-T6 with retreating side AA7075-T651

The significant effects of process parameters on the mechanical and metallurgical properties of dissimilar friction stir welding of AA6082 and AA7075 is studied. A Taguchi orthogonal array design of experiments employed for the optimization of the friction stir welding process parameters to achieve maximum tensile strength. This present investigation has indicated that providing the tool to be tilted to 1⁰ and 2⁰ angle showing good mechanical properties while 0° of lower strength with worm defect. The joint strength was analyzed using ANOVA to emphasis the weld strength. Microhardness survey was also carried out for the understanding of the distribution of hardness across different zones of the weld. The process parameters were correlating with the joint strength by microstructural studies.

Influence of electrode force on metallurgical studies and mechanical properties of resistance spot welded dual phase (DP800) steel joints

Abstract The DP steels are attractive to automotive sectors due to the improved fuel efficiency, occupant’s safety and reducing the car body weight. The resistance spot welding (RSW) most appropriate eco-friendly process for sheet metal and white body car assemblies over fusion welding. The present research work analysis the impact of electrode force on mechanical and metallurgical characteristics of dual phase steel. In this investigation similar joint of DP 800 joints (lap shear and cross shear) specimen fabricated and tensile shear test was evaluated using a universal testing machine. Micro and macrostructure were evaluated optical microscope. The hardness was taken along the weld nugget using Vickers microhardness tester machine. The electrode force was varied at five levels (3.75 MPa to 4.75 MPa). The tensile shear strength is found to be increased with an increase in electrode force up to a certain limit and then it decreases. The microhardness survey revealed that peak hardness in the nugget zone and the hardness is lower in the HAZ. The softening of HAZ is mainly attributed to inter-critical heating during welding, which leads to weld failure.

Diffusion bonding of a titanium alloy to austenitic stainless steel using copper as an interlayer

Diffusion bonding was accomplished between Ti–6Al–4V alloy and AISI 304 austenitic stainless steel utilizing copper as an interlayer in the holding time variety of 45–105 min for 925 °C under 14 MPa load in a vacuum. After bonding, the microstructural study including metallographic examination and energy dispersive spectroscopy, microhardness survey, lap shear strength test, and ram tensile test were accomplished. From the results, holding time is a major influence to develop the microstructural characteristics and improve the joints quality. The occasion of various intermetallic compounds, for example, CuTi, Cu3Ti2, FeTi, Fe2Ti, Cr2Ti has been expected from the ternary phase diagrams of Fe–Cu–Ti and Fe–Cr–Ti. These reaction items were insisted on the X-ray diffraction method. The highest bond strength of 268 MPa was attained for the pair bonded at 90 min holding time. This is a direct result of the better combination of the mating surface. With the expansion in holding time to 105 min, the quality was reduced caused by the expanded volume fraction of discontinuities.

Correlating Tensile Properties with Microstructures of Various Regions in Gas Tungsten Arc Welded AA2014 Alloy

AA2014 is a heat treatable aluminium alloy found its application in light weight structures owing to its superior strength to weight ratio. The alloy was welded with automatic gas tungsten arc welding. The microstructure and mechanical properties of each zone such as parent metal (PM), heat affected zone (HAZ) and fusion zone (FZ) of the weldment were studied using optical microscopy, microhardness survey and micro-tensile testing. The PM with elongated grains with evenly distributed Al2Cu phases showed a tensile strength of 456 MPa and 24% elongation; the HAZ and FZ offered a reduction in strength and ductility. The grain coarsening with segregation of continuous string of Al2Cu along grain boundaries in HAZ and the formation of coarse dendritic grains with continuous network of brittle Al2Cu and a minor fraction of porosity at interdendrite in FZ were attribured to the observed strength reduction in these regions. Keywords: AA2014 alloy; gas tungsten arc welding; optical microscopy; microhardness; micro-tensile testing.

Effect of Severe Plastic Deformation on Microstructure and Mechanical Behaviour of Friction-Welded Structural Steel IS2062

The friction-welded structural steel was subjected to severe plastic deformation by equal-channel angular pressing (ECAP) at ambient condition. Mechanical properties have been experimentally determined and correlated with the microstructure. The friction-welded sample strength got improved up to 70% by ECAP process. In ECAP-processed sample, microhardness survey showed almost similar trend of hardness in all the area of the sample. From the microstructural and TEM analysis, it was understood that the grain refinement and dislocation density have contributed to the strengthening. The generated dislocation density by ECAP process was high in base material than the welded zone and the observation was attested by TEM analysis.

The Effects of TIG Welding Rod Compositions on Microstructural and Mechanical Properties of Dissimilar AISI 304L and 420 Stainless Steel Welds

The usage of AISI/SAE 304L austenitic and 420 martensitic stainless steels is receiving greater interest especially in the defence and navy industries. 304L stainless steels exhibit excellent resistance to oxidizing media, while martensitic 420 alloy provides high strength values besides satisfactory corrosion properties at ambient atmospheres. In this work; 420 quality martensitic stainless steel is TIG (Tungsten Inert Gas) welded with 304L quality low carbon austenitic stainless steel plates. As filler metal dominantly determines the weld metals chemical compositions and final microstructures, 3 different TIG welding rods of ER312, ER316L ve ER2209 are used in welding operations in order to obtain 3 discrete weld metal contents under high purity argon shielding gas. Microstructural inspection, microhardness survey and Charpy V-notch impact tests are applied to all joints after welding operations. The specimen welded by ER2209 TIG welding rod executed the highest impact test results besides exhibiting the lowest micro-hardness profiles at heat affected zones and weld metals. All of the welded specimens weld region hardness profiles were determined to be lower than unwelded 420 martensitic stainless steel base metal.

Characterization of Laser Beam Welded Al<sub>0.5</sub>CoCrFeNi High-Entropy Alloy

High-entropy alloys (HEA), a new generation alloy system offer superior mechanical properties with solid solution strengthening. AlxCoCrFeNi-HEA is one such system being received more attention because of its specific yield strength and ductility. In the present work, Al0.5CoCrFeNi-HEA was prepared by vacuum arc melting. The laser beam welding (LBW) was carried out on 1mm thick forged and homogenized HEA, with a beam power of 1.5 kW and at a traverse speed of 600 mm/min. The microstructural features of different regions of the weld were studied using scanning electron microscopy. The homogenized Al0.5CoCrFeNi-HEA have shown equiaxed grains of average size 60 μm. The weld metal showed a typical weld fusion zone microstructure with dendritic structure with a reduction in BCC phase due to minimal Al and Ni segregation ratio at interdendrites. Micro-chemical analysis with energy dispersive spectroscopy confirmed that there was no major segregation of elements in the weld fusion zone. The microhardness survey performed across the weld evidenced a reduction in hardness, as a consequence of significant reduction in Al-Ni rich hardening factor.

Friction stir welding of thick section Al‐Zn‐Mg‐Cu aluminum alloy

AbstractFriction stir butt welding of 25 mm thick AA7075–T651 plates has been investigated. Careful process parameter selection resulted in single pass, full‐penetration defect free welds. The weld nugget exhibits a significant grain refinement while facing the dissolution of strengthening precipitates. Microhardness survey gives a W‐shaped profile with lower hardness values recorded in the thermo‐mechanically‐affected zone. Tensile fractures occur, again, in the thermo‐mechanically‐affected zone, where minimum hardness occurred. The friction stir welds demonstrate an excellent root bend performance while falling behind base material in face bend test. The welds also displayed outstanding impact toughness compared to that of parent material. It is concluded that defect free single pass friction stir welds can be successfully made on 25 mm thick AA7075–T651 plates.

Microstructure and mechanical properties of similar and dissimilar metal gas tungsten constricted arc welds: Maraging steel to 13-8 Mo stainless steel

Abstract Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding (GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The similar and dissimilar metal welds made in solutionized condition were subjected to standard post weld hardening treatments direct ageing at 485 °C, soaking for 3½ hours followed by air cooling (ageing treatment of maraging steel) and direct ageing at 510 °C, soaking for 4 h followed by air cooling (ageing treatment of 13-8 Mo stainless steel). The joint characterization studies include microstructure examination, microhardness survey across the weldments and transverse weld tensile test. Similar and dissimilar metal weldments responded to both the post weld ageing treatment. After post weld aging, increase in yield strength, UTS and slight reduction in % elongation of similar and dissimilar metal were observed. The observed tensile properties were correlated with microstructure and hardness distribution across the welds.