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.     

Dynamic deformation behavior of aluminum alloys under high strain rate compressive/tensile loading

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as seismic loading are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, dynamic deformation behaviors of the aluminum alloys such as A12024-T4, A16061T-6 and A17075-T6 under both high strain rate compressive and tensile loading conditions are determined using the SHPB technique.     

Effects of overlapping formed via pin-offsetting on friction stir weldability of AA7075-T651 aluminum alloy

Journal of Mechanical Science and Technology - In this study, AA7075-T651 aluminum alloy was joined by friction stir welding (FSW) method, using two different pin offset values, and the...     

Surface integrity in broaching of AA 7075-T651 aluminum alloys

Special features as noncircular hole shapes are manufactured by the broaching process. The rise per tooth varies in different zones of the broaching tool. In this article, the effects of the two main process parameters (cutting speed and rise per tooth) on surface integrity (surface roughness, micro-hardness) and chip morphology will be studied. The experiments have been done on AA7075-T651 aluminum alloy. To investigate the effect of rise per tooth, one of the cutting edges of broaching tool is separated and the broaching process is implemented for nine samples. The samples are broached with three different cutting speeds (6, 12 and 18 m/min) and three rise per tooth (0.02, 0.05 and 0.1?mm). Also, the effect of cutting speed is investigated with a broaching needle (rise per tooth 0.1?mm). The results show that best surface roughness is obtained at cutting speed 12 m/min. The surface roughness will be improved by decreasing the rise per tooth. Also, the surface hardness decreases by increasing the cutting speed. The surface integrity (surface roughness and surface hardness) is comparable for single edge cutting tool and broaching needle. Continuous chips are formed during the broaching process and decreasing the cutting speed cause more compression of the chips.     

Microstructure analysis of aluminum extrusion: grain size distribution in AA6060, AA6082 and AA7075 alloys

Microstructure and material flow of aluminum alloys have a significant influence on the mechanical properties and surface quality. In extrusion of aluminum billets at high temperatures the microstructure is dependent on the alloy and the forming and temperature history. A prediction of grain size and precipitation is of increasing importance in order to design the process by adjustment of parameters such as punch speed, temperatures, and quenching. To give references for microstructure prediction based on material flow, and with it strain and strain rate history, this paper deals with the microstructure during the extrusion process of AA6060, AA6082, and AA7075 alloys. Billets have been partly extruded to axisymmetric round profiles and the microstructure of the press rests consisting of the billet rests in container and die has been considered. Furthermore, these rests have been analyzed to show the material flow, dynamic and static recrystallization based on macro etchings and visible microstructure under different conditions, e.g. as in the area of high strain rate near the container wall, or in dead zones [1]. To allow an accurate simulation of the extrusion process, punch force and temperature conditions during the tests have been measured and are presented in this paper, too.     

Study on rotational fretting wear of 7075 aluminum alloy

Rotational fretting wear tests in a ball-on-flat configuration have been successfully realized on a special rotational fretting rig developed from an ultra-low-speed reciprocating rotational driver. The rotational fretting behavior of 7075 aluminum alloy against 52 100 steel was studied under different angular displacement amplitudes and normal loads. The results showed that both F_t?θ and F_t/F_n curves can be used to characterize the rotational fretting running behavior, which exhibited different curve shapes and variation trends in different fretting running regimes. The rotational fretting behavior of 7075 aluminum alloy was strongly dependent on the angular displacement amplitude, normal load and number of cycles. The wear of 7075 aluminum alloy was characterized by slight attrition in the partial slip regime, while a combination of delamination, abrasive and oxidative wear was found in the slip and mixed fretting regimes. The formation of a central bulge probably due to plastic flow was observed under gross slip condition of the rotational fretting mode.     

Predictions of the optimized friction stir welding process parameters for joining AA7075-T6 aluminum alloy using preheating system

The scope of this investigation is to evaluate the effect of welding parameters on the mechanical properties and microstructural features of 3-mm-thick AA7075-T6 aluminum alloy subjected to gas heating system as a preheating source during friction stir welding. Toward this end, a gas heating system was designed to heat up the weld seam just ahead of rotating tool to soften the material before being stirred. Three welding parameters, five levels, and a central composite design (CCD) have been used to minimize the number of experimental conditions. The joining parameters such as tool rotational speed, welding speed, and shoulder diameter have a significant influence on determining the mechanical properties of the welded joints. It was found that using preheating system mostly can result in higher total heat input into the weld joint and effectively reduces the formation of defects when unsuitable process parameters were used. Also, an attempt has been made to establish the mathematical model to predict the tensile strength and microhardness of the joints. The optimal welding conditions to maximize the final responses were investigated and reported. The results show that the joint fabricated at a rotational speed of 1,050 rpm, welding speed of 100 mm/min, and shoulder diameter of 14 mm exhibited higher mechanical properties compared to other joints.     

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.

     

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.     

Optimization of friction stir welding process of AA7075 aluminum alloy to achieve desirable mechanical properties using ANFIS models and simulated annealing algorithm

Current work deals with experimental investigation, modeling, and optimization of friction stir welding process (FSW) to reach desirable mechanical properties of aluminum 7075 plates. Main factors of process were tool pin profile, tool rotary speed, welding speed, and welding axial force. Also, main responses were tensile strength, yield strength, and hardness of welded zone. Four factors and five levels of central composite design have been utilized to minimize the number of experimental observations. Then, adaptive neuro-fuzzy inference systems (ANFIS) have been used to generate mapping relationship between process factors and main response using experimental observations. Afterward, the developed models were applied as objective function to select optimal parameters, in which the process reaches to its desirable mechanical properties by using the simulated annealing algorithm. Results indicated that the tool with square pin profile, rotary speed of 1,400 RPM, welding speed of 1.75 mm/s, and axial force of 7.5 KN resulted in desirable mechanical properties in both cases of single response and multi-response optimization. Also, these solutions have been verified by confirmation tests and FSW process physical behavior. These verifications indicated that both ANFIS model and simulated annealing algorithm are appropriate tools for modeling and optimization of process.     

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...     

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.     

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。     

Analyzing dissimilar friction stir welding of AA5754/AA7075

AA5754/AA7075 was butt-welded by friction stir welding, and the joint of each weld case was identified by ultimate tensile strength, percentage of elongation, and hardness. Moreover, the significance of each parameter was investigated, and a mathematical relation was constructed by regression analysis. A defect-free joint was achieved in the case of a weld produced with 1000 rpm of tool rotational speed, 80 mm/min of welding speed, and an 22-mm tool shoulder diameter. Most of the failures are located at the bottom of the pin and side of AA7075. The ultimate tensile strength (UTS) decreases with increasing welding speed (WS) or increasing tool rotational speed (TRS). Hardness distribution in the weld zones varied dependent on the nugget zone formation affected by TRS and WS. The present study also investigated the significance and contribution of each parameter on the UTS by analysis of variance (ANOVA). From the results of ANOVA, the conclusion reached is that the all the parameters have a great influence on UTS. The contributions are 41.41 % for WS, 17.58 % for diameter, and 13.28 % for TRS. Moreover, a full quadratic model was constructed between the parameters and the UTS value. The results show that the variation from the predicted values was between 0.41 % and 10.36 %. The strength of the model was analyzed by R-Sq. The achieved R-Sq is 0.892, which means that there is a strong relation between predicted and actual values.     

Surface morphological features of fiber laser cutting of AA2219 aluminum alloy

This article presents a method based on numerical computations for collision avoidance between the toolholder (quill) and workpiece in ball nut grinding in a CAD environment. Besides collision avoidance, the procedure is capable of determining the proper grinding angle with the prescribed safety gap between the toolholder and workpiece. Maple mathematical software is used for the numerical computations with Newton–Raphson, simplified Newton’s method, and built-in Maple fsolve command. The assembly model of the grinding environment was prepared with a Siemens PLM NX system. The interoperation between the assembly model of the CAD system and the mathematical software (parameter transfer and retrieving) was performed by the Maple NX CAD package. The procedures were analyzed for different tool holder and ball nut dimensions, and results demonstrate that it is possible to perform accurate manufacturing parameter specification in an interactive way.