Peak Hardness Values Research Articles

Predictive modeling and optimization of Rockwell hardness of additively manufactured PEEK using RSM, ANFIS and RNN integrated with PSO

The purpose of this research is to investigate the correlation between statistical and machine learning techniques and additive manufacturing, with a specific focus on predicting the Rockwell hardness of FDM-printed polyether ether ketone (PEEK) components. These components have a significant impact on various industries, such as aerospace, biomedical, and automobile. The study analyzes the hardness by conducting experimental analysis of four process parameters, including infill density, layer height, printing speed, and infill pattern. The research utilizes Response Surface Methodology (RSM), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Recurrent Neural Network (RNN) to accurately predict the Rockwell hardness of the printed parts, with an average deviation of less than 5% from the experimental value. The study also investigates how hardness varies with FDM process parameters using contour and surface plots. Furthermore, the study utilizes RNN integrated with the Particle Swarm Optimization (PSO) algorithm to optimize Rockwell hardness. This approach achieved a peak Rockwell hardness value of 66.89 RHN under conditions of 80% infill density, 0.1mm layer height, 25 mm sec−1 printing speed, and an octet infill pattern. Microstructural examinations and test results corroborate the findings derived from parametric analysis and optimization efforts.

Effect of repeated-tempering induced martensite on the microstructural evolution in 17–7 PH stainless steel

Single long-time tempering and triple tempering processes have been applied to 17–7 PH stainless steel (chemical composition: Fe-0.09C-16.4Cr-7.7Ni-0.9Al, wt%) to investigate the effects of the stability of austenite on subsequent martensitic transformation and aging hardening. The as-received steel was composed of 0.55 austenite and 0.45 martensite (volume fraction). Scanning electron microscopy images showed that the volume fraction of martensite (up to 0.98) in triple-tempered specimens ((0.5 h @ 760 °C) × 3) was about 0.15 higher than that (0.83) in single-tempered ones ((1.5 h @ 760 °C) × 1). The results clearly indicate the effectiveness of the triple-tempering process in progressively improving martensitic transformation. Direct observation of the austenite/martensite interface has provided evidence that the preceding martensitic transformation induces accommodation strain into the adjacent austenite, which brings about the mechanical stabilization of austenite but will facilitate the succeeding martensitic transformation after three consecutive tempering operations. The relevant microstructural evolution has been explored and discussed. Furthermore, subsequent aging at 565 °C led to precipitation hardening associated with the formation of NiAl nanoparticles. The triple-tempered specimen yielded the higher peak hardness value (424 HV) in 20 min, significantly faster than the single-tempered specimen, which took 90 min to reach the lower one (357 HV). The corresponding number density of NiAl nano-precipitates and dislocation densities of martensite at various aging times have been examined by transmission electron microscopy to elucidate the benefits of the triple tempering process for precipitation strengthening.

Effect of destability time on microstructure and properties of hypoeutectic high chromium cast iron.

The present work investigated the effect of destabilization time on the mechanical properties and microstructure evolution of high chromium cast iron, and scanning electron microscopy and electron probe microanalysis techniques were employed. The results show that the hardness of hypoeutectic high chromium cast iron is related to the size and volume fraction of secondary carbides precipitated from the matrix. The hardness of the alloy continues to rise due to the continuous increase of the volume fraction of the secondary carbide at the initial stage of destabilization. The alloy reaches its peak hardness value at 950 °C and 1000 °C for 1 hour holding time. The solid solubility of carbon and alloying elements in the matrix increases as the holding time extends, resulting in a large number of carbides redissolved into the matrix, making the hardness of the alloy decrease; the hardness of the alloy at 14 h is less than that at 10 min. Under 1050 °C, the size and density of the secondary carbide increase significantly; extending the holding time will lead to the continuous reduction of the carbide rod that provides strength, thus, the hardness curve shows a downward trend.

Influence of melon shell ash reinforcement on the mechanical and microstructural characteristics of recycled aluminium matrix composites

This study produced a composite using melon shell ash as reinforcement on recycled Aluminium waste cans matrix. The melon shell particulate additions to the matrix were done in wt.% of 0, 10, 5, 15 and 20. The mechanical behaviour of the composite demonstrates that the tensile values increased as the particulate addition increased to 15% wt. to reach a maximum of 113MPa but dropped at the 20% addition. The impact energy on the other hand increases marginally at 5% particulate addition and increases slightly higher with the addition of reinforcement of 10% wt to attain a maximum value of 77J. However, a further increase in the melon shell ash to 15% wt and 20% wt reduced the impact energy. The hardness values of the composites at all the % wt. additions were generally higher than that of the unreinforced Aluminium with the peak hardness value of 57.2BHN obtained at 10% wt. addition. The density of the composites decreases as the % wt. of the melon shell ash particles increases. The improved mechanical properties and lower density of the composites achieved in this study are significant factors in developing strong and lightweight engineering materials for industrial applications.

Effect of Sn Addition on the Microstructure and Age-Hardening Response of a Zn-4Cu Alloy

The aim of this research is to assess the influence of Sn inclusion on the microstructure evolution and age-hardening response of a Zn-4Cu alloy. This is the first study to correlate the age-hardening response to the microstructure of Zn-4Cu alloy reinforced with different Sn contents. A series of Zn-4Cu-Sn alloys were successfully fabricated with different Sn concentrations in the range of 0.0–4.0 wt.% using permanent mold casting. The microstructure of Zn-4Cu-Sn alloys was investigated by means of a scanning electron microscope (SEM) attached with an energy dispersive spectroscope (EDS) and X-ray diffraction (XRD) line profile analysis. At room temperature, the Vickers microhardness measurements were used to assess the age-hardening response of alloys. The results show that the microhardness of the Zn-4Cu (ZC) binary alloy increases a little bit from 76 to 80 HV as the aging time increases from 2 to 128 h, respectively. For aging times up to 16 h, the microhardness of all Sn-containing alloys decreases but then increases again. The lowest hardness belongs to the ZC-1.5Sn alloy, and the Sn-Zn-3.0Sn alloy has the highest; the other alloys fall somewhere in between. At high aging times (64 and 128 h), the microhardness of all Sn-containing samples increased continuously with an increasing Sn content from 0.0 to 3.0 wt.%. When the Sn-containing alloys (3.5 and 4.0 wt.% Sn) were aged for 64 and 128 h, the hardness declined by 7.94% and 8.90% compared to their peak aging hardness values, respectively. By considering the structural changes that occur in the Zn-4Cu-Sn alloys, the reasons for the observed variations in microhardness data with increasing Sn content and aging time were elucidated. X-ray diffraction (XRD) data was analyzed to determine the zinc matrix’s lattice parameters, c/a ratio, and unit cell volume variations.

Low-temperature bonding between F82H and Cr assisted by metastable Cr interlayers applied by pulsed laser deposition

The joining of F82H and pure Cr metal has been demonstrated at temperatures as low as 798 K, assisted by the prior application of a thin metastable Cr interlayer to both bonding surfaces using pulsed laser deposition. Bonded F82H/Cr interfaces were characterised by SEM-EDS and TEM analysis, with respect to diffusion behaviour, chemical composition and microstructure. At higher bonding temperatures, an interface layer formed on the Cr side of the joint, which was rich in M23C6, though its structure and thickness was different depending on whether Cr interlayers were applied. As the bonding temperature was decreased stepwise, the interface layer thickness reduced to a minimum of ∼60 nm and appeared to adopt a film-like structure. Although the chemical composition of the thinner interface layers could not be determined, they were most likely M23C6 in a film-like form, which subsequently formed particles, and then columns, as the bonding temperature and interface layer thickness increased. Hardness around the interface increased as compared with the bulk F82H and Cr, though the peak hardness value decreased as the interface thickness decreased. The hardness of bulk F82H and Cr was similar before and after bonding at all temperatures, suggesting little impact on mechanical properties. Diffusion of Cr into F82H and Fe into Cr was not detected at any of the conditions tested, and the original tempered lath martensite microstructure of F82H appeared to have been retained.

Peak hardness stability analysis of Al7075 alloy dispersed with Ni coated duralumin powder during natural aging phenomena

This technical paper presents the successful reinforcement of nickel (Ni) coated duralumin powder in an Al7075 matrix using the liquid stir casting technique and property stability obtained by heat treatment. Ni coating is performed by electroless nickel plating technique where 8 μm coating thickness was observed to be the minimum required to prevent dissolution of the reinforcements (duralumin powder) in the matrix (Al7075). During stir casting it was observed to uniformly disperse the coated duralumin powder up to 7 wt.%. Al7075 alloy and composites were artificially aged with solution heat treatment (SHT) performed at 450 °C for 4 h, water quenched and then aged at 120, 150 and 180 °C. Al7075 alloy and composites were naturally aged for 24 weeks in atmospheric temperature after peak aging. Composites aged at 120 °C exhibited superior results and considered as optimum aging temperature compared to those aged at 150 and 180 °C. Peak hardness values in 7075-7Dp+8T composite improved by 108% and 7075-7Dp+10T composite improved by 110% when compared to peak aged (at 120 °C) Al7075 alloy. Moreover, composites with coated reinforcement displayed a higher resistance to natural aging, with reductions of 53.5 and 54.4% in natural aging tendency compared to the naturally aged Al7075 alloy for 7075-7Dp+8T and 7075-7Dp+10T composites respectively. However, an increase in Ni coating thickness beyond the optimal 8 μm did not significantly improve as cast and peak hardness or natural aging resistance. XRD analysis confirmed that there is presence of CuAl2, CuAl2Mg, Mg2Si, and MgZn2 phases in peak-aged (120 °C) 7075-7Dp+8T sample. Considering the limited impact on property enhancement and the financial burden associated with thicker coatings, a coating thickness of 8 μm is recommended as compared to 10 μm.

Experimental analysis of hardness and tensile characteristics of copper reinforced AA6061 stir cast composites subjected to thermal and deformation assisted heat treatments

Aluminium alloy 6061 based composites reinforced with a varied weight percentage of copper particulates are fabricated utilizing a liquid metal stir casting technique. The collective influence of copper reinforcement, age hardening and low temperature thermomechanical treatment on AA6061 was investigated. The age hardened composites displayed better hardness and ultimate tensile strength than as cast composites. Thermomechanical treatment of the composites further enhanced the mechanical properties and hence showed better results over age hardened composites. The study revealed that an increase in the deformation enhanced the hardness and strength of the composite while the aging time to achieve the peak hardness was reduced. Both age hardened and thermomechanically treated composites with 6 wt.% copper reinforcement indicated the best peak hardness and UTS values at the lower aging temperature of 100 °C. The thermomechanically treated composite with 6 wt.% Cu, 15% deformation aged at 100 °C showed 80 and 69% increase in hardness and UTS, respectively, over as cast composite. Fracture surface analysis of the as cast, age hardened, and thermomechanical treated composites showed a mixed mode of fracture dominant with the brittle failure.

Gas nitriding behavior of refractory metals and implications for multi-principal element alloy design

Multi-principal element alloys (MPEAs) comprise a large, flexible compositional space that enables tuning of their chemistry, structure, and properties. To facilitate the development of nitriding-based surface-enhancement strategies that harness a broad compositional space, this study examined the gas nitriding behavior of Hf, Mo, Nb, Ta, Ti, and Zr as a function of time, temperature (750 and 1000 °C), and nitriding potential (i.e. ammonia-to-hydrogen ratio). These metals were selected because they have a strong driving force to form nitrides, and appear in many promising refractory MPEA compositions. The nitriding temperatures were selected based on the phase transformation temperature of Ti and Zr, and the nitriding potentials were chosen such that all elements are expected to form nitrides. Mass gain measurements indicate that all six elements follow parabolic kinetics. The microstructure observations and quantitative microchemical analysis show formation of dense and well-adhered compound layers for Mo, Nb, and Ta. Thick diffusion zones appear in Hf, Ta, Ti, and Zr, and diffusion coefficients were fit to the composition profiles. Partial delamination of the compound layer occurred for Ti and Zr. Peak hardness values above 30 GPa are obtained in the dense compound layers, and the solute hardening of the underlying alloy is correlated with the nitrogen content. The results provide insight into the dynamics of nitride compound formation relative to interstitial dissolution of nitrogen, and are discussed in the context of MPEA composition and processing design.

Examining the mechanical response and microstructural evolution of heat-treated Al-5Si-3Cu alloy for automotive applications

ABSTRACT Aluminium-Silicon (Al-Si) based alloys are gaining more prominence among researchers for automotive applications. In this paper, the impact of copper alloying element and artificial ageing treatment on the mechanical response and microstructural evolution of Al-Si based alloys synthesised from aluminium scrap are examined, as there is need to gear up the urge for the usage of metallic scraps for production of alloys for automotive applications. The as-cast Al-Si alloy and its form with copper as alloying element (1.5% and 3% Cu) were produced using liquid metallurgy route. Solution heat treatment was carried out at 500℃ and artificial ageing was carried out at 190℃ for 0.5, 1, 1.5, 2 and 2.5 h. Mechanical properties and microstructural characterisations of the as-cast and artificially aged forms of Al-Si based alloys were performed. The hardness tests were performed according to ASTM A29/A29M–15. Impact strength was determined according to ASTM D256. Tensile tests were performed based on ASTM E8. Microstructures of the synthesised Al-Si alloys were examined using optical microscopy and scanning electron microscopy techniques. In as-cast condition of the Al-5Si-Cu alloy, impact strength increases with increase in copper content. Al5Si-Cu alloy with 3% copper content and artificially aged at 190°C for 2.5 h exhibited the highest impact strength. Hardness number increases with the increase in copper content up to 1.5% and the ageing time. Additional increase in the ageing time yielded decrease in the hardness number. Results revealed that artificial ageing enhances mechanical and microstructural characteristics of the Al-Si alloys. Ageing treated Al-Si alloys exhibited peak hardness, impact strength and ultimate tensile strength (UTS) values of 77.47 kgf/mm2, 17 J/mm2 and 137.80 MPa, respectively. The obtained results are indicative of mechanical properties enhancement when compared with as-cast Al-Si alloys with maximum hardness, impact strength and UTS of 43.71 kgf/mm2, 12.92 J/mm2 and 123.18 MPa, respectively. Significant improvement in mechanical properties was achieved in Al-Si-Cu alloy with copper content and artificial ageing when compared to that without copper inclusion. This may be attributed to the evolution of equiaxed precipitates and the fact that copper-rich Al-Si-Cu alloys promotes formation of precipitation strengthening phases of α-AlFeMnSi. This study shows that the mechanical properties of Al-5Si-Cu alloys produced using aluminium scrap-based materials were enhanced using artificial ageing treatment and the benefit can be utilised for automotive applications.

Dual role of trace elements in magnesium dissolved age hardened A356 alloy on microstructure and peak micro hardness

The present work reflects the effects of trace addition of copper (up to 1 wt.%) and zinc (0.5 wt.%) on the microstructure and hardness property of heat treated A356 (Al-7Si) alloy. Small amount of zinc and copper was introduced into A356 in both atomic form (alloy) and powder form (composite) and its age hardening behaviour were investigated. To enhance the wettability during composite fabrication and solid solution strengthening in alloys, a small quantity of magnesium (1 wt.%) was added. The main objective of this study is to introduce lower melting point zinc reinforcement into A356 matrix alloy by copper coating of zinc particles and then reinforcing it into A356 matrix. All stir cast specimens were subjected to T6 treatment by solutionizing at 520 °C for 2 h followed by 60 °C water quench and then aging at 100 and 200 °C to determine peak hardness value. Microstructure analysis showed that a minimum 1 wt.% copper was required to form Al2Cu intermetallic phase during solidification resulting in finer grain structure with hardness improvement. Under as-cast conditions, a maximum hardness of 85 VHN was obtained in 1 wt.% copper reinforced composite. Under peak aged conditions, aging at 100 °C showed 116% hardness improvement in 1 wt.% Cu reinforced composite.

TITANIUM ADDITION AND AGEING INFLUENCE ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Cu-10Ni ALLOY

— The need to develop alloys with enhanced properties that will perform efficiently has continually become the major concern. In this study, the influence of Ti addition on the microstructure and mechanical properties of Cu-10Ni alloy was investigated. Cu-10Ni alloy was altered by adding Ti in the concentrations of 0.1, 0.2, 0.3, and 0.4wt%. The as-cast samples of Cu-10Ni alloy were solution treated at 900oC for 2 hr, quenched in water, and then aged at three different temperatures (400oC, 450oC and 500o ) for 2hr. Microstructural characteristics were observed using metallurgical microscope, and scanning electron microscope equipped with EDS, while tensile strength, hardness, impact strength and ductility as a function of mechanical properties were determined. Adding Ti contents in Cu-10Ni alloy and ageing at different temperatures greatly increased the properties and grain refinement of the alloy. The improvement in properties were due to slight promotion of precipitation and occurrence of enhanced TiNi3 particles after ageing treatment. The as-cast Cu-10Ni alloy had a peak value of 163MPa tensile strength, 127BHN hardness, and 142J impact strength at 0.1%Ti. Under the ageing condition, the samples with 0.4%Ti had peak tensile strength, hardness, and impact strength values of 574MPa, 193BHN, and 138j, respectively. The variation in the values of the tested properties of the alloys was measured on the role of the ageing temperature. The Ti addition promotes the growth of precipitates, which refines the microstructure during the ageing process and results in an excellent improvement of the properties of the Cu-Ni alloys.

Achieving high strength and large elongation in a strip casting microalloyed steel by ageing treatment

The microstructure and mechanical properties of a Nb–V microalloyed steel produced by strip casting in as-coiled and aged conditions were investigated using scanning electron microscopy, electron backscatter diffraction, X-ray diffraction, transmission electron microscopy, atom probe tomography and tensile tests. Tensile test results show that, after ageing at 650 °C for 5 min, accompanying an increase of yield strength from 698 ± 3.6 MPa to 758 ± 7.9 MPa, the elongation increases from 7.1 ± 0.4% to 12.6 ± 0.4% simultaneously. Microstructural analysis shows that both the as-coiled and aged specimens possess a microstructure predominantly comprising a mixture of acicular ferrite and bainitic ferrite. Hardness tests for specimens aged at different temperatures show very similar peak hardness values but higher ageing temperature requires less time for peak ageing. Ageing treatment leads to a decrease of dislocation density, which is responsible for the enhancement of elongation for aged specimens, while Nb–N-rich and Nb–V–N-rich clusters develop successively during ageing, which contributes to the increase of yielding strength after ageing. The strengthening contributions from solid solution, dislocations, grain boundaries and clusters were calculated, and the results indicated that dislocations and grain boundaries are the dominant strengthening mechanisms for the current strip casting steels.

Homogenization effect on precipitation kinetics and mechanical properties of an extruded AA7050 alloy

Abstract In this study, effect of homogenization on precipitation kinetics and mechanical properties during aging in AA7050 alloy was investigated. The billet material produced by direct chill method was homogenized at 470 °C for 12–20 h and then extruded to form T-profile. The electrical conductivity of the alloy aged at 120 and 185 °C for 0–36 h were measured and precipitation kinetics were calculated based on the relationship between increased electrical conductivity and amount of precipitates during aging. Time dependent precipitation fraction change curves using Avrami equations revealed that precipitation accelerated as the homogenization time increased due to increased nucleation and growth rates of precipitates. Peak hardness values in aging were reached depending on the increase in homogenization time, however, lower peak hardness (∼185 HV) was determined at 185 °C aging compared to the obtained ones (195–197 HV) at 120 °C aging. Depending on the increase in homogenization time, an increase trend in strength was detected in peak aged alloys. The application of longer time homogenization and subsequent aging caused an increase in strengths. The studied homogenization and aging conditions could be a useful guide for achieving the highest strength and ideal elongation values in commercial practice for the AA7050 alloy.

Optimization of preheating temperature for TiB2 reinforcement on the preparation of stir cast LM4 + TiB2 composites and effect of artificial aging on hardness improvement using ANOVA

This work emphasizes the optimization of preheating temperature of TiB2 reinforcement powder with LM4 composites, and statistical analysis for predicting hardness improvement during aging treatment using ANOVA, are illustrated in this article. A two-stage stir casting procedure was used to fabricate LM4 + TiB2 (1, 2 and 3 wt.%) composites. The impact of preheating TiB2 reinforcement powder at various temperatures such as 600, 500, 450, 350 and 250 °C, to attain uniform distribution of reinforcements in the matrix was studied. Optical microstructure analysis clearly shows that the optimum preheating temperature of TiB2 powder for effective preparation of composites is 350 °C for 30 min without agglomeration of reinforcement particles. After successful preparation of composites, the as-cast samples were subjected to single-stage and multistage solutionizing treatments and then artificially aged at 100 and 200 °C to obtain peak hardness. Micro Vickers Hardness test was done to calculate the hardness of both age hardened LM4 alloy and its composites and results were analyzed. An increase in wt.% of TiB2 (1–3%), the hardness of composites increased, and multistage solutionizing treatment followed by artificial aging at 100 °C was proven to achieve the highest peak hardness value for LM4 + 3 wt.% TiB2 composites. Compared to as-cast LM4 alloy, 80–150% increase in hardness was observed when aged at 100 °C and 65–120% increase in hardness was observed at 200 °C during SSHT and MSHT, respectively. ANOVA was performed with wt.%, solutionizing type, aging temperatures as factors, and peak hardness as the outcome. From the results, it can confirm that all three factors contributed effectively for achieving the peak hardness. R2 value validates that the factors account for 100% of the variance in the hardness results.

Effects of Heat Treatment on the Hardness Properties and Microstructure of Al-6505 Alloy

The effects of heat treatment on the ageing response, hardness properties and the microstructure development of Al-6505 alloy have been investigated. In order to study these effects, the alloy sample was solution treated at 550°C for 30 minutes and then quenched into cold water at room temperature followed by artificially aged at elevated temperature of 100 oC, 185 oC and 300 oC. The ageing response of Al-6505 alloy was monitored using Vickers hardness test. The distribution of the precipitates formed in Al-6505 alloy was monitored by transmission electron microscopy (TEM). The results showed that time to reach peak hardness and peak hardness values decreased as the ageing temperatures increased. It was found that increasing in hardness values of the alloy were due to needle-shaped precipitates formation during ageing treatment. Prolonged ageing time to over-aged condition resulting in increased the size but reduced the number of precipitates; as a result the hardness of Al-6505 alloy was reduced. The effects of heat treatment on the ageing response, hardness properties and the microstructure development of Al-6505 alloy have been investigated. In order to study these effects, the alloy sample was solution treated at 550°C for 30 minutes and then quenched into cold water at room temperature followed by artificially aged at elevated temperature of 100 oC, 185 oC and 300 oC. The ageing response of Al-6505 alloy was monitored using Vickers hardness test. The distribution of the precipitates formed in Al-6505 alloy was monitored by transmission electron microscopy (TEM). The results showed that time to reach peak hardness and peak hardness values decreased as the ageing temperatures increased. It was found that increasing in hardness values of the alloy were due to needle-shaped precipitates formation during ageing treatment. Prolonged ageing time to over-aged condition resulting in increased the size but reduced the number of precipitates; as a result the hardness of Al-6505 alloy was reduced.

Age hardening heat treatment behavior of as-cast Mg–Zn–Al alloys

Magnesium alloys have generated renewed interest as a light alloys; replacing some conventional structural materials for weight reduction in applications like aerospace, automotive and electronics industries. In interior components and powertrains, cast alloys are widely used and represent more than 99% of magnesium alloys used today, whereas only a few wrought products are used. Mostly in automotive applications, Mg-engine block can noticeably reduce the weight and consequently its fuel consumption and environmental impact. Due to solid-state precipitates, these alloys are strong in nature and are produced by an age-hardening heat treatment process. In the present work the age hardening behavior of the as cast Mg–Zn–Al alloys (ZA85 alloy) in the composition of 8 wt. %Zn, 5 wt. %Al has been investigated. Through the differential thermal analysis (DTA) studies, it has been found out that dissolution temperature of ternary eutectic precipitates is present in the alloy. Based on the DTA results, the as cast samples have been solutionised at 360 °C temperature for different intervals of time. Solutionising time has been optimized from the enthalpy values of un-dissolved precipitates. The solution treated samples have been then aged at temperature of 180° C for different time intervals. From the peak hardness values, the ageing conditions have been optimized.

Role of dissimilar Ni-based ERNiCrMo-3 filler on the microstructure, mechanical properties and weld induced residual stresses of the ferritic/martensitic P91 steel welds joint

In the present investigation, a detailed microstructure and mechanical behaviour study for P91 welded joint were investigated. The welded joint was produced using the Gas Tungsten Arc welding (GTAW) process with dissimilar Ni-based filler IN625 (ERNiCrMo-3). For microstructure characterization of the weld joint, optical microscopy and scanning electron microscopy were utilized. The effort was made to get a relationship between microstructure and mechanical properties variation. The residual stress measurement was also carried out for both the condition by using the hole-drilling method. To evaluate the mechanical properties, tensile testing and Charpy testing was done at room temperature. The weld joint developed with dissimilar Ni-based filler processes the austenitic microstructure having equiaxed dendrites in bulk weld metal and columnar and cellular dendritic structure near the interface. The segregation of the alloying elements like Mo and Nb was also confirmed along the inter-dendritic areas. The welded joint qualified the tensile test and Charpy test with average value of 580 ± 12 MPa and 65 ± 5 J, respectively in as-welded. However, a reduction was observed in tensile strength and Charpy toughness after the PWHT. A significant variation in microhardness was measured across the welds joint, and peak hardness was measured about 344 HV in the coarse-grained heat affected region while in weld metal it was 263 HV. The peak hardness value in HAZ and variation in hardness also get reduced after the PWHT. In the weld metal, a significant variation in the residual stresses was measured along the thickness with peak magnitude 250 MPa and 172 MPa for longitudinal and transverse stress, respectively in the as-welded condition. A significant reduction in peak residual stresses (longitudinal stress and transverse stress) was obtained after the PWHT.

Effect of Heat Treatment on the Microstructure, Mechanical Properties, and Corrosion Resistance of Friction Stir Processed Al-Zn-Mg-Cu-Sc-Zr Alloy

Post-heat treatment was conducted on the Al-Zn-Mg-Cu-Sc-Zr alloy treated by friction stir processing (FSP) to optimize its strength and corrosion resistance. Different post-heat routes had significant bearing on the phase composition of the FSP sample, while its fine equiaxed grain structure could be retained during post heating. Enhanced strength of the FSP sample was obtained by post-heat treatments. The FSP sample after T6 treatment (artificial aging to peak hardness value after solid solution treatment) exhibited the highest strength in virtue of its high precipitation strengthening effect, and the high ductility of the FSP sample could be retained after solid solution treatment. Furthermore, the FSP sample presented better corrosion resistance after artificial aging and T6 treatment by reducing its solution atom numbers.

Simultaneous Optimization of Laser Energy and Coating Thickness in Surface Alloying of Al with Fe

In the two-step deposition technique of the laser surface alloying process, the alloying elements are introduced onto the bulk material’s surface. In such process, two main parameters determine the alloying quality: the thickness of the coating and the laser energy supplied onto the specimen. In this work, the laser surface alloying of aluminium (Al) with iron (Fe) is carried out by optimizing both parameters. This is accomplished by assessing the improvement in the hardness after laser treatment. In general, the thicker coating desires higher laser energy to cause surface melting and sequentially diffusion of Fe into molten Al to occur. This is indicated by the linear relationship between the thicknesses for the peak hardness value with the laser energy whereby the optimum energy shifted to higher energy for a thicker coating. The increase in laser energy increases Fe particle’s chance to migrate via diffusion into the bulk Al substrate. However, at 140μm the optimized energy reaches a peak value at 455mJ which is the maximum energy to be supplied in this process before the coating is lost due to excessive ablation. For thicker coatings, the laser’s action does not penetrate enough onto the substrate to cause sufficient melting of the Al surface for alloy formation. The maximum hardness obtained was 40.8 HV at the optimum condition for 140μm thickness treated with 455 mJ. The formation of an alloyed compound is further confirmed by x-ray diffraction technique whereby compounds such as AlFe, Al13Fe4, and AlFe6Si are present in the treated specimens.