Dual-rotary fretting wear behavior of 7075 aluminum alloy

Friction and wear behavior of dual-rotary fretting (DRF) combined by torsional and rotational fretting modes have been investigated. Such fretting mode is essentially achieved by changing tilt angles of the rotary axis and varying rotary angular displacement amplitudes The DRF behavior has been characterized from the dynamic behavior, wear damage, third-body behavior, wear mechanisms. The running condition fretting map (RCFM) of DRF fretting wear was established by using the tilt angles and angular displacement amplitudes. The evolution of the wear volume vs the tilt angle under varied angular displacement amplitudes was quantificationally measured. In addition, the competition between the local wear and fatigue (cracking, wear) has been discussed in detail. The results indicated that the damage of 7075 aluminum alloy induced by DRF was strongly dependent upon the tilt angle and the angular displacement amplitude.     

Formation of fretting fatigue cracks in 7075-T7351 aluminum alloy

Fretted regions in 7075-T7351 aluminum alloy test specimens subjected to cyclic fatigue loading have been examined by scanning electron microscopy. Fatigue cracks generally formed at or near the boundaries of the fretted regions, often in patches of surface markings having a ripple or chevron-like appearance.     

Quantitative analysis of fretting fatigue degradation in 7075-T6 aluminum alloy

Fretting fatigue failures are commonly observed in the aviation industry. The objective of this study was to understand the fretting fatigue mechanism by characterization of fretting fatigue degradation to gain insight into the process of crack formation from pits in 7075-T6 aluminum alloy. This paper focuses on the quantitative analysis of fretting fatigue degradation in terms of pit depths and dominant crack formation. For 60 percent of the specimens, the dominant crack nucleated from a pit other than the maximum-depth pit observed on the fracture surface.     

Abrasive and fretting wear resistance of aluminum alloy specimens manufactured by laser microcladding

In this article, the results of investigations of abrasive wear resistance and wear under the fretting of the samples obtained by the method of laser microcladding have been presented. The material for sample preparation was powder of Al–Si hypereutectic alloy with the following composition: 70–74 wt % Al and 26–30 wt % Si. The influence of the structure and phase composition of AlSi30 alloy on wear resistance under the conditions of abrasive wear and wear under fretting conditions has been shown.     

Corrosion and wear of 6082 aluminum alloy

The corrosion and corrosive wear resistance of 6082 wrought aluminum alloy against 410 stainless steel counterface in 0.01 M NaCl solution with different concentrations of sodium molybdate dihydrate solution (0, 0.01, 0.1 and 0.5 M), were studied. The experimental results indicated that the increase in sodium molybdate dihydrate acted as an inhibitor in the 0.01 M NaCl solution resulting in a significant decrease in the corrosion current, meaning improved corrosion resistance. During the corrosive wear under free corrosion conditions of 6082 aluminum alloy specimens against 410 stainless steel counterface, the addition of sodium molybdate dihydrate inhibitor, leads to a decrease in friction coefficient of the examined pair of materials. The dominant wear mechanisms of the aluminum alloy were mainly observed to be plastic deformation and abrasion. These wear mechanisms coexisted with pitting corrosion phenomena, on the surface of this alloy.     

Study on rotational fretting wear of bonded MoS2 solid lubricant coating prepared on medium carbon steel

The rotational fretting wear behaviors of the bonded MoS₂ solid lubricant coating and its substrate steel were comparatively studied under varied angular displacement amplitudes, constant normal load, and rotational speed. Dynamic analysis in combination with microscopic examinations was performed through SEM, EDX, XPS, optical microscope, and surface profilometer. The experimental results showed MoS₂ changed the fretting running regimes of substrate. The friction coefficients of MoS₂ were lower than those of the substrate. For MoS₂, the damage in partial slip regime was very slight. The damage mechanism of the coating in slip regime was main abrasive wear, delamination, and tribo-oxidation.     

Study on transition between fretting and reciprocating sliding wear

An experimental investigation was conducted to find the associated changes in characteristics of wear before and after the transition between fretting and reciprocating sliding wear. A set of experiments were carried out using a AISI 52100 steel ball rubbing against a plate specimen made from the same steel under dry condition. Wear coefficient, wear volume, coefficient of friction, profile of the scars and wear debris were analyzed. The results displayed that there were significant differences in wear coefficient, wear volume, profile of the wear scars and wear debris before and after the transition. Wear coefficient and wear volume at a constant sliding distance were found to be the most appropriate for identifying the transition amplitude between fretting and reciprocating sliding wear.     

基于宽频激励电磁声谐振7075铝合金板厚检出概率

电磁超声换能器(EMAT)换能效率低、激发信号弱,而基于长周期激励信号以产生声波共振的电磁声谐振技术(EMAR)虽然可以提高接收信号的信噪比,然而可能导致主脉冲加宽并扩大超声波检测盲区,降低测量精度.本文应用一种宽频激励电磁声谐振技术(BE-EMAR)和一种Halbach阵列纵波EMAT,以单周期宽频激励作为EMAT输...     

7075铝合金选区激光熔化研究现状

现今航空航天等领域对复杂精密零件的需求逐步增加,传统的加工方式已无法满足这一趋势。选区激光熔化(Selective Laser Melting, SLM)基于逐层叠加的原理可一次性成型复杂件,因此对于这类零件具有广泛的应用前景。7075铝合金是航空航天领域常用的一种高强铝合金,由于高强铝合金热导率高,对激光反射率大,易氧化,有很强的热裂倾向等特点,导致SLM成型7075铝合金难度大。然而市场对其越来越大的需求,近几年发展迅速。主要从工艺优化和添加形核成分方面总结了近几年国内外7075铝合金选区激光熔化的研究现状,并阐述了存在的问题和发展趋势。     

Damage and failure characterization of 7075 aluminum alloy hot stamping

7000 series high strength aluminum alloys are increasingly used in manufacturing automobile body parts to meet the more stringent demands for automobile lightweight. Hot stamping of 7000 series high strength aluminum alloys is a complex thermal-mechanical coupling process and precise simulation is needed to predict material fracture. To obtain damage model of 7075 aluminum alloy in hot stamping, five different stress triaxiality specimens were designed. The fracture strain, critical strain and average stress triaxiality of different specimens were obtained by the hybrid finite element simulation and experiment (FE-EXP) method. GISSMO model of 7075 aluminum alloy at 400 °C was established. Compared with the experimental results of U-shaped part hot stamping under different lubrication conditions, the calibrated GISSMO model was demonstrated to predict the damage behavior of 7075 aluminum alloy during high temperature deformation accurately.

     

基于LS-DYNA的7075铝合金汽车保险杠碰撞仿真分析

为了使汽车轻量化,将7075铝合金应用于汽车保险杠系统中。通过有限元软件LS-DYNA对不同厚度保险杠模型的低速对中碰撞进行仿真分析,选用2.5 mm厚加强板和2.0 mm厚齿状横梁,相比原钢质保险杠质量下降20.5%。最后对所选保险杠进行对中碰撞仿真分析。结果显示该保险杠不仅质轻,而且吸能充分,满足碰撞安全要求。     

Viscoplastic behavior of AA7075 aluminum alloy at high strain rate

Journal of Mechanical Science and Technology - The flow stress increases with the increase in strain rate. This phenomenon is the strain rate effect of plastic deformation. Hopkinson experiment...     

Effect of oil supply on fretting wear

Fretting wear of lubricated flat steel surfaces (100 mm × 100 mm) was studied using a specially prepared test rig. The amplitudes of reciprocating sliding and the apparent contact pressure were 0.1–0.75 mm and 10 MPa respectively. The specimen surfaces were given various heat treatments and were mesh grooved for oil supply. Gear oil was fed to the sliding surfaces. Ungrooved surfaces gave severe fretting wear under the experimental sliding conditions used. However, significant reduction in fretting wear was obtained by grooving the surface. The effect could be obtained only when the spacing between the grooves was small, presumably because the oil was fed to the whole contact region owing to the smaller spacing.     

A generalized fretting wear theory

Combined impact-sliding fretting wear is a complex phenomenon due to the random nature of the excitation force and the self-induced tribological changes. Available models, which relate wear losses to the process variables, are empirical in nature and bear no physical similarity to the actual mathematical and physical attributes of the wear process. A generalized fretting wear theory is presented to mathematically describe the fretting wear process under various modes of motion; impact, sliding and oscillatory. This theory, which is based on the findings from the fracture mechanics analysis of the crack initiation and propagation processes, takes into consideration the simultaneous action of both the surface adhesion and subsurface fatigue mechanisms. The theory also accounts for the micro-, and macro-contact configuration of the fretting tribo-system. The closed form solution requires the calibration of a single parameter, using a limited number of experiments, to account for the effect of environment and the support material. The model was validated using experimental data that were reported for Inconel 600 and Incoloy 800 materials at room and high temperature environment, and for different types of motion. The results showed that model can accurately predict wear losses within a factor of ±3. This narrow range presents better than an order of magnitude improvement over the current state-of-the-art models.     

Frequency effects in fretting wear

The effect of frequency of vibration on fretting wear has been investigated in the 10 – 1000 Hz range with additional experiments at 20 000 Hz. Fretting tests were performed with two materials, a low carbon steel (AISI 1018) and an austenitic stainless steel (AISI 304). The experiments showed that two cases of fretting contact can be distinguished and related to the displacement amplitude. If the amplitude is low, the contact situation is characterized by partial stick at the interface. At these conditions the wear rate (measured as the volume of material removed per cycle) is little affected by frequency. However, in low amplitude fretting material damage by surface degradation and fatigue crack initiation is usually of more concern than the actual wear itself. Both of these parameters are found to be greatly accelerated by an increase in frequency. In high amplitude fretting, in contrast, gross slip occurs at the interface and wear becomes the dominant damage mode. At these conditions variations in frequency appear to have little effect on fretting wear and related mechanisms. Therefore, in the case of fretting at high displacement amplitudes, it may be possible to apply high frequency fretting to obtain accelerated testing conditions.     

Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed(HVOF) technique WC-17 Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope(SEM), energy dispersive X-ray spectroscopy(EDX), and X-ray diffractrometry(XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy(OM), and surface topography. The experimental results reveal that the WC-17 Co coating adjusted the boundary between the partial slip regime(PSR) and the slip regime(SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17 Co coating in prevention of rotational fretting wear.     

Metallographic analysis of fretting fatigue damage in Ti-6Al-4V MA and 7075-T6 aluminum

Fretting fatigue tests were conducted utilizing axial fatigue load application at various maximum fatigue stress levels and normal pressures. Materials investigated were titanium Ti-6A1-4V mill annealed (MA) and aluminum 7075-T6. Subsequent to testing, the specimens were sectioned and metallographically examined to investigate the relationship between fretting damage, fretting induced cracking and reduction of specimen fatigue life.At all maximum fatigue stress levels investigated a given amount of fretting damage was required before any fatigue life reduction occurred. Presumably, the damage leads to the development of cracks in the fretted areas. Metallographie studies of the fretted areas have revealed that multiple cracks form and are propagated by fatigue. Some evidence was found to indicate that fretting debris is forced into the microcracks as they develop, thus explaining, in part, the significant reduction in life caused by the fretting.     

Effect of machining parameters on surface roughness and tool wear for 7075 Al alloy SiC composite

In the present study, an attempt has been made to investigate the influence of cutting speed, depth of cut, and feed rate on surface roughness during machining of 7075 Al alloy and 10 wt.% SiC particulate metal-matrix composites. The experiments were conducted on a CNC Turning Machine using tungsten carbide and polycrystalline diamond (PCD) inserts. Surface roughness of 7075Al alloy with 10 wt.% SiC composite during machining by tungsten carbide tool was found to be lower in the feed range of 0.1 to 0.3 mm/rev and depth of cut (DOC) range of 0.5 to 1.5 mm as compared to surface roughness at other process parameters considered. Above cutting speed of 220 m/min surface roughness of SiC composite during machining by PCD tool was less as compared to surface roughness at other values of cutting speed considered. Wear of tungsten carbide and PCD inserts was analyzed using a metallurgical microscope and scanning electron microscope. Flanks wear of carbide tool increased by a factor of 2.4 with the increase of cutting speed from 180 to 240 m/min at a feed of 0.1 mm/rev and a DOC of 0.5 mm. On the other hand, flanks wear of PCD insert increased by only a factor of 1.3 with the increase of cutting speed from 180 to 240 m/min at feed of 0.1 mm/rev and DOC 0.5 mm.