Alloy Friction Research Articles

Study on corrosion fatigue properties and fracture characteristics of 7075 aluminum alloy FSW joint

Taking 7075-T6 aluminum alloy friction stir welding joint as the research object, the microstructure, 3.5 wt % NaCl solution corrosion fatigue life and corrosion fatigue fracture characteristics were studied, and the corrosion fatigue performance and fracture process of 7075 aluminum alloy friction stir welding joint were analyzed. The results showed that: the S-N curve equation of corrosion fatigue of 7075-T6 aluminum alloy friction stir welded joint is lgN=5.845-0.014S, With the increasing of stress amplitude, the corrosion fatigue life decreased greatly. The corrosion fatigue crack originated in the thermal affected zone of the joint, gradually expanded and finally broke in the welded core zone of the joint. There were multiple crack sources in the corrosion fatigue fracture, and with the influence of stress concentration, the crack source originated in the corrosion pit. The high stress aggravated the corrosion damage of the corner part of the sample, led to more serious corrosion than that of the plane position. Obvious intergranular fracture and fatigue striation appeared in the crack growth zone. Under the combined action of corrosive medium and alternating load, the crack growth zone suffered the most serious corrosion, and the anodic dissolution occurred at the grain boundary, resulting in the morphology characteristics of “rock candy” and “ant nest”. Instantaneous fault zone was brittle fault,and there were a lot of cleavage steps and secondary cracks in this zone, the pore morphology appeared in the second phase particle distribution region.

Tribological properties of structural alloys for the heat exchange equipment parts subjected to fretting

Trobological characteristics of sliding friction in stainless steel and titanium alloys in dry and water lubricated conditions have been determined. The character of the coefficient of friction variation with load and the duration of tests have confi rmed the prevailing wear mechanism in these materials to be frictional fatigue fracture that in the case of titanium alloys is accompanied with adhesive interaction and plastic plowing. The frictional fatigue curves built in a result of this investigation make possible to estimate the materials tribological longevity.

Investigation into reciprocating dry sliding friction and wear properties of bulk CoCrFeNiMo high entropy alloys fabricated by spark plasma sintering and subsequent cold rolling processes: Role of Mo element concentration

For the first time, a systematic investigation into effect of Mo element concentration on the crystal lattice constant, microhardness, and reciprocating dry sliding friction and wear properties of face-centered cubic (FCC) single phase based CoCrFeNiMo high entropy alloys (HEAs) were specifically conducted in the present study. Both the lattice constant and microhardness were found to increase with the amount of Mo element. Moreover, increasing Mo element concentration in the CoCrFeNiMo HEA was beneficial into reductions of friction coefficient and its specific wear rate when sliding wear against the GCr15 steel balls in a dry condition at room temperature. Interestingly, all studied CoCrFeNiMo HEAs exhibited almost the same wear mechanisms, which strongly depended on the applied normal load during sliding wear tests. Mo element addition had a remarkable influence on the cross-sectional microstructures after sliding wear, and grain coarsening in the middle transition region was effectively retarded by increasing the amount of Mo element in the CoCrFeNiMo HEA.

Wear Resistance Enhancement of Al6061 Alloy Surface Layer by Laser Dispersed Carbide Powders.

In this paper, results of the experimental study on improving wear resistance in sliding friction of Al-based alloy are presented. The technique used involves the formation of a metal matrix composite (MMC) in the alloy surface layer by laser dispersion of carbide powders such as WC, TiC and SiC. For WC and TiC MMC surface coatings fabricated under conditions typical for most of the technologically relevant solid-state lasers (wavelength range of 0.8–1.1 μm), the nearly inversely proportional dependence of the required laser energy density on the powder mass density is observed. Highly homogenous distribution of powder particle content (up to 40%) in the MMC surface coatings of a thickness between 0.8 and 1.6 mm obtained by multiple scanning is observed in the cross-section of specimens processed within a rather narrow parameter window. Tribological tests and comparison to untreated material reveal wear resistance increases by five- and ten-fold, observed in samples with laser-dispersed TiC and WC powders, respectively. Results indicate that substantial modification and reinforcement of the surface layer can be achieved in Al alloy in a one-step process without substrate preheating.

Influence of Crystallographic Orientation on Nanoscale Friction and Wear Mechanisms of the AZ91 Alloy

In the present study, nanoscale friction and wear behavior of the AZ91 alloy with respect to crystallographic orientations (basal, pyramidal and prismatic) were examined. The hardness of different crystallographic orientation was measured using nanoindentation. Load-dependent friction and wear behavior was investigated using atomic force microscopy (AFM). Electron back scattered diffraction (EBSD) was used to investigate the deformation behavior post-indentation and wear. A strong anisotropy in hardness, friction and wear with respect to crystallographic orientation was observed. The basal oriented grain was found to be most wear-resistant followed by prismatic and pyramidal oriented grains. The friction results corroborated the wear data. Additionally, the model proposed by Song et al. has been used to quantify the orientation dependence of friction values. Finally, it is anticipated that these results will enable the development of orientation informed surfaces for controlling the wear and friction response of materials.

Effect of laser textured surface with different patterns on tribological characteristics of bearing material AISI 52100

Chrome steels are used in bearings since they possess high strength and wear resistance. However, when those parts are in service, failure happens due to sliding friction before the lifetime. To improve the durability of the American Iron and Steel Institute (AISI) 52100 chromium steel, in this work, the effect of laser surface texturing (LST) was analyzed. With the different patterns of circle and ellipse comparing with the untextured samples, the wear behavior was investigated using the pin-on-disc tribometer. The lubricant used for wear analysis is semisolid lithium grease National Lubricating Grease Institute lubricant (SKF NLGI-3). Sliding wear analysis was conducted at different loads of 10 N, 30 N and 50 N for the sliding speed of 750 r/min and 1400 r/min. The wear morphology was analyzed using a scanning electron microscope(SEM). The roughness of the samples was found using a white light interferometer. The effect of different patterns like circle and ellipse, alter the friction and wear properties of chromium alloy was observed compared with the untextured samples. LST shows considerable reduction in friction and wear for ellipsoidal pattern compared with the circular pattern because of wear debris and lubricant getting trapped.

Stochastic Tensile Failure Analysis on Dissimilar AA6061-T6 with AA7075-T6 Friction Stir Welded Joints and Predictive Modeling

The issue of weld solidification cracking in fusion welding of highly alloyed aerospace aluminum alloys is eliminated in friction stir welding (FSW) because the base materials do not melt during welding. However, in FSW, the weld joint quality characteristics are found with highly sensitive for the variation of process variables. Therefore, this investigation deals with the analysis of the significance of FSW processing conditions, construction of stochastic tensile failure probability models for dissimilar AA6061-T6 with AA7075-T6 aluminum alloy friction stir welded joints, and postulation of their statistical predictive models. The experimental results have shown an effective mixing at the interface of both base alloys attributed to efficient bonding and resulted in the mechanical properties with the weld joints. A lowest tensile strength was achieved for the weld joint produced by the straight cylindrical profiled tool pin, which is 24.51% lower than the UTS of AA6061-T6 unwelded alloy while 59.09% lower than the AA7075-T6 unwelded alloy. The survival probability of the weld joints fabricated at 30 mm/min is 92% for 260 MPa applied stress, but the weld joints fabricated at 20 and 40 mm/min are 70 and 40%, respectively. For 50% reliability of the weld joint, the maximum allowable stress values suggested are 270, 288, and 255 MPa for processed at of 20, 30, and 40 mm/min welding speeds, respectively. The application stresses beyond 290 MPa, and the survival probability of the weld joints fabricated at 40 mm/min is zero. Empirical models postulated for tensile strength, ductility, and microhardness were fund with a reasonable agreement with their experimental measurements statistically. The derived reliability and empirical models can be used to estimate the reliability of the welded joints and predict their mechanical properties to estimate and enhance the functional performance of the welded structures in automobile and aerospace applications.

Multi-response optimization of process parameters in friction stir welding of dissimilar aluminum alloys by Grey relation analysis (AA 6061-T6 & AA5083-H111)

In the fusion of different solid-state alloys (150X150X6 mm) friction stir welding techniques are carried out using rotational speeds, transverse speeds and varying pin profiles. Emerging trends to join different alloys, heat-treated (AA 6061-T6) and non-heat can be treated (AA 5083-H111) is an important part of the joining dissimilar alloys. In this investigation, the experimental design using the response surface method must predict the parameters of the optimized welding method by using non-linear multi responsive optimization techniques. This technique, while using applications for experimental observations developed the mathematical model, must achieved the welding standards using optimal input and output parameters. These results use a confirmation process with reference to the ANOVA model which is used to develop and find out the optimal value of defect-free welding. It has developed a multivariate mathematical analysis for the relationship between the mechanical properties of the model. And using a scanning electron microscope from a microstructure must reveal dominant problems such as tunnel formation defects, voiding, plunging, etc.

Multi-directional forging and aging treatment effects on friction and wear characterization of aluminium-bronze alloy

An aluminium bronze alloy was processed by multi-directional forging (MF) and aging treatment. The microstructure, strength, hardness, ductility and friction and wear character were investigated. The strength and hardness were enhanced and the friction coefficient was decreased after MF, but the wear resistance inferior to that of coarse-grained (CG) types. Lower work hardening is the main factor that leads to a lower the wear resistance in the fine-grained structure aluminium bronze alloy. After MF and aging, the fine-grained structure aluminium bronze alloy with higher sliding wear resistance was due to higher strength, hardness, ductility and work hardening, though higher friction coefficient.

Evolution of process parameters in friction stir welding of AA6061 aluminum alloy by varying tool eccentricity

The evolution of processing parameters by varying tool eccentricity in AA6061 alloy friction stir welding was examined using a combination of detailed force/torque measurements and thermal history as well as high-speed camera (HSC) observations. Tri-axial forces show larger oscillations during the steady-state phase of welding if the tool eccentricity is increased. However, the tool torque remains similar for up to 0.4 mm eccentricity versus the aligned tool even with varying weld speed. In situ HSC observation indicates that tool eccentricity is reduced during the welding process for larger eccentric setups. Stir zone thermal measurements reveal that the temperature peaks and stabilizes near the solidus temperature of the AA6061 base material.

Study on the Precipitation Behavior of Precipitates of 7075 Aluminum Alloy Friction Stir Welding Joint

In this work, the microhardness of 7075 aluminum alloy friction stir welding (FSW) joint was measured by a micro vickers hardness tester, the microstructure of the joints was characterised by microscope, the precipitated phases among the welding nugget zone (WNZ), thermal mechanical affected zone (TMAZ), heat affected zone (HAZ) were affirmed by X-ray diffractometer (XRD) and the lattice fringe of transmission electron microscopy (TEM) high resolution image. Based on this, the precipition behavior of precipitated phases was studied. The results show that the microhardness distribution of the 7075 aluminium alloy FSW joints is heterogeneous in comparison with the base metal (BM). The precipitates in the joint mainly include MgZn rod shape and AlCuMg in elliptical shape. In the WNZ, the main precipitate is AlCuMg, and the fine grain strengthening effect is better, so the microhardness in this zone is relatively high. In the TMAZ, the quantity of AlCuMg decreased while the MgZn2 increased relatively in comparison with the WNZ. At the same time, the effect of the fine grain strengthening was weakened, though the strain hardening increased. Therefore, the microhardness in the TMAZ still decreased. In the HAZ, the quantity of MgZn2 increased furtherly, and there is no strain hardening and fine grain strengthening, so the microhardness of the HAZ was the lowest among the FSW joints. Besides, through comparative tests, the optimal process parameters of friction stir welding of 7075 aluminum alloy were obtained.

A Review on Fracture Mechanics of AA2024 Aluminium Alloy Friction Stir Welding

A Review on Fracture Mechanics of AA2024 Aluminium Alloy Friction Stir Welding

Evidence of Inverse Hall-Petch Behavior and Low Friction and Wear in High Entropy Alloys

We present evidence of inverse Hall-Petch behavior for a single-phase high entropy alloy (CoCrFeMnNi) in ultra-high vacuum and show that it is associated with low friction coefficients (~0.3). Grain size measurements by STEM validate a recently proposed dynamic amorphization model that accurately predicts grain size-dependent shear strength in the inverse Hall-Petch regime. Wear rates in the initially soft (coarse grained) material were shown to be remarkably low (~10–6 mm3/N-m), the lowest for any HEA tested in an inert environment where oxidation and the formation of mixed metal-oxide films is mitigated. The combined high wear resistance and low friction are linked to the formation of an ultra-nanocrystalline near-surface layer. The dynamic amorphization model was also used to predict an average high angle grain boundary energy (0.87 J/m2). This value was used to explain cavitation-induced nanoporosity found in the highly deformed surface layer, a phenomenon that has been linked to superplasticity.

Effect of different types of graphene coatings on friction and wear performance of aluminum alloy

In this work graphene coatings have been deposited on aluminum alloy samples to investigate whether they can improve wear strength and promote friction reduction, which means components reliability and efficiency. Tribological performance has been tested by pin-on-disk wear tests. Three procedures to coat the samples have been explored. One is based on transferred graphene method and the other two are based on percolative graphene. Results show that graphene coatings last little time onto the sample surface, though strongly reducing the coefficient of friction of aluminum samples as far as they endure.

Influence of High-Frequency Impacting and Rolling on Friction and Wear Behavior of 2A12 Aluminum Alloy

High-frequency impacting and rolling (HFIR) as a new surface strengthening treatment has been paid more and more attention. 2A12 aluminum alloy was processed by HFIR with different parameters. The effect of HFIR on friction and wear behavior of 2A12 aluminum alloy was investigated. Results showed that the surface roughness value of HFIR processed samples was decreased compared to the original samples. Compared with the original samples, the maximum surface microhardness of the HFIR treated samples ultimately increased by about 12.4%. The depth of hardened layer of about 135 ??m can be obtained by HFIR treatment. The wear mechanisms of the HFIR-free samples were oxidation wear, abrasive wear and severe adhesive wear. The wear mechanisms of the HFIR-treated samples were abrasive wear, light adhesive wear and oxidation wear. Experimental results indicated that HFIR treatment is an efficient way to enhance the wear resistance of the 2A12 aluminum alloy.

Structural morphology of Al-Mg-Si alloy friction stir welds through tool eccentricity

In this work, the microstructure development in the stir zone of Al-Mg-Si alloy is evaluated while employing tool eccentricity during friction stir welding. Low dislocation density with dispersoids were observed in the inner band region of the stir zone produced with aligned tooling. On the other hand, a high dislocation density with Mg2Si precipitates can be observed in the same region of the stir zone when a tool eccentricity of 0.2 mm was utilized. The discrepancy is attributed to the enhanced shearing activity imposed on the material during the welding process.

Effects of base metal state on the microstructure and mechanical properties of Al–Mg–Si alloy friction stir-welded joints

Al–Mg–Si alloys with different heat treatment states were used as base metals (BMs) in investigating the effect of BM state on the microstructure and mechanical properties of Al–Mg–Si alloy friction stir-welded (FSW) joints. The Al grains and insoluble phases of the FSW joints were not affected by BM state, but the compositions of the precipitated phases in the heat-affected zones (HAZs) and nugget zones (NZs) depended on the phase compositions of the BMs. The FSW joint that was welded using the BM with water quenching (WQ) and artificial aging state exhibited the greatest hardness among the joints at the same zones because of the high densities of the β″ phases in the BM, the fine and high densities of the β′ phases in the HAZ, the high number of solution atoms, and the formation of Guinier–Preston zones in the NZ. Moreover, the joint exhibited the highest yield strength because of the high hardness of its HAZ, which is the fracture location in FSW joints. The FSW joint that was welded using the BM with WQ and natural aging state exhibited the highest ultimate tensile strength and tensile elongation because of its high structural uniformity.

The mechanism of rotational and non-rotational shoulder affecting the microstructure and mechanical properties of Al-Mg-Si alloy friction stir welded joint

Butt joining of Al-Mg-Si alloys with 6.0 mm in thickness was made with conventional rotational shoulder friction stir welding (RSFSW) and non-rotational shoulder friction stir welding (NRS-FSW) process, respectively, and the resultant mechanism of different shoulders affecting the microstructure and mechanical properties of joint was discussed. A new zone named “triangle zone” (TZ) in the RSFSWed joint was first clearly defined, while the shoulder and pin affected zone (SPAZ) did not exist in the NRS-FSWed joint. The distribution of average grain sizes in each zone of the joints (“M” shape) and the changes in the proportion of high angle grain boundaries (HAGBs) (“W” shape) are unified with the typical “W” shape distribution of microhardness in the joints. Compared to rotational shoulder, the non-rotational shoulder significantly reduced the width of softened area. In particular, the microstructure of the joints by NRS-FSW with triple facets on the pin surface is finer, denser and more homogeneous. The tensile strength coefficient of the joint welded by NRS-FSW and NRS-FSW with the pin of triple facets increased by 2.3% and 11.6%, respectively, compared to the joint welded by RSFSW. Accordingly, the fatigue performances increased by 1.72 times and 3.19 times, respectively.

Steel tubular friction damper and vibration reduction effects of double-layer reticulated shells

A steel tubular friction damper (STFD) is proposed for vibration reduction in large-span spatial structures. The effects of the amplitude of the applied displacement, the pre-tightening force of the high-strength bolts, and the material of the friction plates on the hysteretic behaviour of the STFD are analysed experimentally. The single-cycle energy consumption increases and the equivalent stiffness decreases with increasing displacement amplitude. In addition, the single-cycle energy consumption and equivalent stiffness of the STFD increase with increasing pre-tightening force. Both the single-cycle energy consumption and the equivalent stiffness of the STFD with aluminium alloy or brass friction plates are larger than that of the STFD with steel friction plates. Then, a mechanical model of the STFD is established for further numerical analysis. Several structural members in a 40-m-span double-layer reticulated shell are replaced with STFDs to provide vibration reduction. Optimal arrangement of STFDs is studied based on additional modal damping ratio. The effects of the replacement rate, earthquake intensity and various ground motions on the vibration reduction effect are investigated via numerical analyses. The reduction ratio first increases and then decreases with increasing replacement rate, and the best performance is observed at a replacement rate of 10%. The vibration reduction effect of the STFDs is more obvious for strong ground motions than for weak ground motions. Under various ground motions, the vibration reduction effect of the STFDs is better for the two ordinary ground motions than for the four long-period ground motions selected herein.

Friction and wear behaviors of TC4 alloy with surface microporous channels filled by Sn-Ag-Cu and Al2O3 nanoparticles

To overcome the poor tribological performance of titanium alloys and broaden their applications in the rapidly developing aerospace industry, this paper studies the friction and wear behaviors of TC4 alloy with surface microporous channels filled by Sn-Ag-Cu (SAC) and Al2O3 nanoparticles using the dry sliding tests. Moreover, the synergistic lubricating mechanism of SAC4 and Al2O3 nanoparticles is also investigated in detail. The results show that TC4 alloy with surface microporous channels filled by SAC4 (50Sn-45Ag-5Cu) and 6 wt% Al2O3 nanoparticles (TC4-SACA3) presents excellent antifriction property and wear resistance over a wide range of temperatures and applied loads. Especially at 400 °C-10 N, TC4-SACA3 can obtain the smallest friction coefficients of 0.185 and the minimal wear rate of 3.6 × 10−5 mm3N−1 m−1, which is attributed to the synergistic effect of SAC4 and Al2O3 nanoparticles. During the sliding process, SAC4 can precipitate from the microporous channels under the heat-force driving and then gradually form a smooth lubricating film on the friction surface. Meanwhile, some Al2O3 nanoparticles wrapped by lubricant SAC4 can improve the load carrying capacity of lubricating film, and the other exposed Al2O3 nanoparticles on the friction surface play a role of “micro-bearings” between the friction pairs.