Fatigue Life Estimation of High Strength 2090-T83 Aluminum Alloy under Pure Torsion Loading Using Various Machine Learning Techniques

The ongoing effort to create methods for detecting and quantifying fatigue damage is motivated by the high levels of uncertainty in present fatigue-life prediction approaches and the frequently catastrophic nature of fatigue failure.The fatigue life of high strength aluminum alloy 2090-T83 is predicted in this study using a variety of artificial intelligence and machine learning techniques for constant amplitude and negative stress ratios(R?1).Artificial neural networks(ANN),adaptive neuro-fuzzy inference systems(ANFIS),support-vector machines(SVM),a random forest model(RF),and an extreme-gradient tree-boosting model(XGB)are trained using numerical and experimental input data obtained from fatigue tests based on a relatively low number of stress measurements.In particular,the coefficients of the traditional force law formula are found using relevant numerical methods.It is shown that,in comparison to traditional approaches,the neural network and neuro-fuzzy models produce better results,with the neural network models trained using the boosting iterations technique providing the best performances.Building strong models from weak models,XGB helps to predict fatigue life by reducing model partiality and variation in supervised learning.Fuzzy neural models can be used to predict the fatigue life of alloys more accurately than neural networks and traditional methods.

Microstructure Distribution Characteristics of High-Strength Aluminum Alloy Thin-Walled Tubes during Multi-Passes Hot Power Backward Spinning Process

The microstructure of the thin-walled tubes with high-strength aluminum alloy determines their final forming quality and performance. This type of tube can be manufactured by multi-pass hot power backward spinning process as it can eliminate casting defects, refine microstructure and improve the plasticity of the tube. To analyze the microstructure distribution characteristics of the tube during the spinning process, a 3D coupled thermo-mechanical FE model coupled with the microstructure evolution model of the process was established under the ABAQUS environment. The microstructure evolution characteristics and laws of the tube for the whole spinning process were analyzed. The results show that the dynamic recrystallization is mainly produced in the spinning deformation zone and root area of the tube. In the first pass, the dynamic recrystallization phenomenon is not obvious in the tube. With the pass increasing, the trend of dynamic recrystallization volume percentage gradually increases and extends from the outer surface of the tube to the inner surface. The fine-grained area shows the states of concentration, dispersion, and re-concentration as the pass number increases. .

Numerical Simulation of Warm Forming Behavior of High Strength Aluminum Alloy 7075

Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry.However,material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming.Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075),constitutive equations with strain rate sensitivity at 140,180 and 220 ℃ are developed.Anisotropic yield criterion Barlat 89 is used in the simulation.Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140,180 and 220℃are performed.Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results.Punch force and displacement predicted from simulation are compared with the experimental data.Simulation results agree with experimental results,so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.

METAL INERT GAS WELDING OF 2519-T87 HIGH STRENGTH ALUMINUM ALLOY

20 mm thick plates of 2519-T87 high strength aluminum alloy have been welded.The effects of the compositions of filler wires,the heat input and the compositions of shielding gas on the mechanical properties and microstructure of the welded joint have been investigated.The results indicate that finer microstructure,better mechanical properties and higher value of hardness of HAZ can be obtained by using lower heat input.The use of Ar/He mixed shielding gas has several advantages over pure Ar shielding gas.With the increase of the proportion of He in the mixed shielding gas, the grain size of the weld metal as well as porosity susceptibility decreases.When the volume ratio of He to Ar reaches 7：3,the porosity and the grain size of weld metal reach the minimum,and the porosity can be further reduced by filling some CO2.

Stability of fiber laser-MIG hybrid welding of high strength aluminum alloy

The effect of fiber laser on MIG arc was investigated with 8 mm 7075-T6 high strength aluminum alloy as base material.The arc shape,droplet transfer form and electrical signal in the process of MIG welding and laser-MIG hybrid welding were analyzed.The stability of the hybrid welding process was evaluated by standard deviation analysis.The results show that with the increase of laser power,a large number of laser-induced plasma enters the arc column area,providing more conductive channels,which makes the heat of MIG arc more concentrated and the short circuit transition disappear.Due to the continuous effect of laser,the keyhole becomes a continuous electron emission source,and a stable cathode spot will be formed near the keyhole,which enhances the stability of MIG arc at the base current state.By using the method of standard deviation analysis,the voltage standard deviation of single MIG welding arc and laser-MIG hybrid arc within 4 seconds was calculated.The standard deviation of single MIG arc voltage was 1.05,and the standard deviation of MIG arc voltage in laser-MIG hybrid welding was 0.71–0.86,so the hybrid welding process was more stable.

Microstructure and mechanical property of resistance spot welded joint of aluminum alloy to high strength steel with especial electrodes

Dissimilar material joining of 6008 aluminum alloy to H220 YD galvanized high strength steel was performed by resistance spot welding with especial electrodes that were a flat tip electrode against the steel surface and a domed tip electrode upon the aluminum alloy surface. An intermetallic compound layer composed of Fe2Al5 and FeAl3 was formed at the steel/ aluminum interface in the welded joint. The thickness of the intermetallic compound layer increased with increasing welding current and welding time, and the maximum thickness being 7. 0 μm was obtained at 25 kA and 300 ms. The weld nugget diameter and tensile shear load of the welded joint had increased tendencies first with increasing welding current （ 18 -22 kA） and welding time （ 50 - 300 ms）, then changed little with further increasing welding current （ 22 - 25 kA） and welding time （300 -400 ms）. The maximum tensile shear load reached 5.4 kN at 22 kA and 300 ms. The welded joint fractured through brittle intermetallic compound layer and aluminum alloy nugget.

Simulation on the deformation controlling of T-joint LBW with auxiliary heat source for high strength aluminum alloy

To avoid the angular deformation of aluminum alloy T-joint weldments, a new method named welding with auxiliary heat source is proposed. The welding simulation is performed with the commercial finite element software Abaqus and FORTRAN programme encoding a special conical heat source with Gaussian volumetric distribution of flux. The influence of the local model on the temperature, residual stress, and welding deformation distributions is investigated. The findings show that angular deformation achieved through numerical computation completely consists with the experimental result which has proved the effectiveness of the finite element methods developed. Various measurements performed on small-scale welded test specimens provide a data base of experimental results that serves as a bench mark for qualification of the simulation result. Finally, the residual stress and strain states in a T-joint are predicted.

Process of friction-stir welding high-strength aluminum alloy and mechanical properties of joint

The process of friction-stir welding 2A12CZ alloy has been studied. And strength and elongation tests have been performed, which demonstrated that the opportunity existed to manipulate friction-stir welding parameters in order to improve a range of material properties. The results showed that the joint strength and elongation arrived at their maximums (331 MPa and 4%) at 37.5 mm/min and 300 rpm. As welding parameters changing, joint tensile strength and elongation had similar development. Hardness measurement indicated that the weld was softened. However, there was considerable difference in softening degree for different joint zone. The weld top had lower hardness and wider softening zone than other zone of the weld. And softening zone at advancing side was wider than that at retreating side.

Recent progress in corrosion protection of friction stir welded high-strength aluminum alloy joints

Friction stir welding （FSW） has been widely used in many industries, with which high-strength aluminum alloys can be well joined. However, the corrosion resistance of FSW high-strength Al alloy joints is relatively poor, which limits their industrial applications. The joints shall be protected against corrosion. In this review, therefore, the current status and development of corrosion protection for FSW high-strength Al alloy joints are presented. Particular emphasis has been given to different protection methods ： lowering heat input, post-weld heat treatment, surface modification and spray coatings. Finally, opportunities are identified for further research and development in corrosion protection of FSW high-strength Al alloy joints.

7000系高强铝合金微观组织结构对应力腐蚀行为和机制影响的研究进展

7000系(Al-Zn-Mg-Cu)高强铝合金是铝合金中强度最高的系列之一,应力腐蚀开裂(SCC)是影响其服役安全稳定性的关键因素。综述了应力腐蚀开裂的阳极溶解机制和氢致开裂(HIC)机制,总结了7000系铝合金中的组织结构对合金SCC行为及机制的影响;从合金化学成分、热处理、预应变、表面处理等方面对SCC敏感性的影响出发,论述了不同组织结构对SCC行为的影响。提出了降低7000系高强铝合金SCC敏感性的重点研究方向:通过优化合金元素、使用新型的热处理工艺和表面处理技术等方法合理调控合金的微观组织结构,进而延长合金的使用寿命,使材料受到更好地保护。

Surface nanocrystallization of 7A52 aluminum alloy welded joint

As a means of surface modification process, metal surface nanocrystallization （MSN） has attracted widespread attention and enjoyed a great prospect. However, currently little research is carried out regarding MSN of welded joint. The processes of high energy shot peening （HESP） technology and ultrasonic impact treatment （UIT） were carried out to achieve joint surface nanocrystallization. The grain size of before and after the welded joint surface nanocrystallization were comparatively analyzed with X-ray diffractometer, the surface deformation layer thickness of before and after the welded joint surface nanocrystallization were comparatively analyzed with optical microscopy, the surface hardness of before and after the welded joint surface nanocrystallization were comparatively analyzed with micro hardness machine. The results show that both of the processes can achieve welded joint surface nanocrystaUization and the weld after HESP have smaller grain size, larger deformation layer thickness and higher hardness values than those after UIT. However, HESP is restrained by the shapes and sizes of welding materials, so the UIT process is preferred to use in the general engineering practical applications.

7150高强铝合金自支撑搅拌摩擦焊接头成形与组织研究

为解决高强铝合金搅拌摩擦焊(friction stir welding,FSW)背部需刚性支撑的问题,设计了自支撑搅拌摩擦焊分体式焊具,由上轴肩、搅拌针和下支撑体组成。采用下支撑体的结构设计可以进行7150-T77511铝合金的无垫板支撑FSW,并消除了传统FSW背部的弱连接缺陷。通过焊接工艺参数优化,当转速为550 r/min,焊接速度为500 mm/min时,焊缝成形良好,无内部缺陷。焊缝横截面组织呈“哑铃”形,工件上下层分别受上轴肩和下支撑体作用产生上焊核区和下焊核区,这两个区域的晶粒尺寸相近,相比焊核区晶粒更细小。

Elevated temperature endurance and creep properties of extruded 2D70 Al alloy rods

The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ultimate strength. The fracture morphology of some selected samples after testing at different elevated temperatures was observed by scanning electron microscopy （SEM）. The results indicate that, as the test temperature increases, the elevated temperature enduring strength of 2D70 Al alloy decreases gradually. In a comparison between 150 C and 240 C, the notch enduring strength drops from 375 to 185 MPa and the smooth enduring strength drops from 337 to 130 MPa. Enduring strength is not sensitive to the notch. The notch sensitivity ratio （NSR） coefficient is in the range of 1.119 to 1.423 from 150 C to 240 C. The creep test results show that, as the test temperature increases from 150 C to 240 C, the creep ultimate strength of 2D70 Al alloy rods drops gradually from 312 to 117 MPa.

Interfacial characterization of resistance spot welded joint of steel and aluminum alloy

The dissimilar material resistance spot welding of galvanized high strength steel and aluminum alloy had been conducted. The welded joint exhibited a thin reaction layer composed of Fe2Al5 and Fe4Al13 phases at steel/aluminum interface. The welded joint presented a tensile shear load of 3.3 kN with an aluminum alloy nugget diameter of 5.7 mm. The interfacial failure mode was observed for the tensile shear specimen and fracture occurred at reaction layer and aluminum alloy fusion zone beside the interface. The reaction layer with compounds was the main reason for reduction of the welded joint mechanical property.

Tensile and high-cycle fatigue properties of spray formed Al10.8Zn2.9Mg1.9Cu alloys after two-stage aging treatment

Based on the investigation of the tensile properties of spray formed ultra-high strength Al10.8Zn2.9Mg1.9Cu alloys, the high-cycle fatigue properties under different theoretical stress concentration factors were investigated, the fatigue fracture surfaces and microstructures were observed, and the fatigue mechanism was discussed. The results indicate that the ultimate tensile strength of spray formed Al10.8Zn2.9Mg1.9Cu alloys can reach up to 730?740 MPa, and the elongation is about 8%?10% under the condition of two-stage aging treatment. For the stress ratio is 0.1, the maximum stress for 107 cycles is over 400 MPa and 120 MPa, when the theoretical stress concentration factor is 1 and 3, respectively.

7xxx高强铝合金熔化焊研究进展

针对7xxx高强铝合金的焊接研究现状,主要从TIG,MIG,激光焊及激光-电弧复合焊4类熔化焊工艺进行了介绍;从焊接缺陷、焊缝成形、接头软化、疲劳性能及耐蚀性等方面详述了7xxx高强铝合金熔化焊过程中存在的问题。对于7xxx高强铝合金的TIG,MIG,激光焊及激光-电弧复合焊,焊接缺陷、焊缝成形质量差及接头中强化相熔解等因素都会导致接头发生软化、耐蚀性变差及疲劳寿命降低;通过优化焊接工艺参数,减少焊接缺陷,改善焊缝成形质量,有利于改善接头的软化、耐蚀性差及疲劳寿命低等问题。选用合适的焊丝(含Ti,Zr元素及Er,Sc稀土元素)使焊缝产生沉淀强化、细晶强化及固溶强化,可改善接头软化的问题;采用适当的焊后热处理,改善强化相的尺寸、形态及分布状态,也可改善接头软化的问题;而采用适当的焊后热处理,还可以改善接头的耐蚀性。

Effect of variable polarity frequency on 2A14-T6 aluminum alloy welds using HPVP-GTAW process

Hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） for 2A14-T6 high strength aluminum alloy was carried out and the effects of variable polarity frequency with constant pulse current frequency 40 kHz on weld bead geometry, microstrueture and microhardness were analyzed. Experimental results indicate that, compared to that of the conventional VP-GTAW process, the weld depth and ratio of weld depth to width are improved significantly by the variable polarity frequency in the HPVP-GTAW process, which the ratio of weld depth to width is improved by 36% at equal variable polarity frequency of 100 Hz, and improved by 55% with that of 200 Hz. Weld microstructure and microhardness distribution are changed obviously with the increase of variable polarity frequency. In the conventional VP-GTA W process, the grains in weld central zone are coarser, and the microhardness in weld central zone and fusion zone is about 95 HV and the lowest 82 HV, respectively. The microhardness is enhanced to a certain extent both in the weld central zone and fusion zone with the variation of variable polarity frequency in the HPVP-GTAW process due to the refinement and uniformity of weld microstructure. With the variable polarity frequency of 600 Hz, the microhardness in weld central zone and fusion zone reaches nearly 110 HV and 97 HV, respectively.

Effect of pre-recovery on microstructure and properties of rolled Al-12.18Zn-3.31Mg-1.43Cu-0.20Zr-0.04Sr aluminum alloy

The independently designed and manufactured ultra-high-strength aluminum alloy Al-12.18 Zn-3.31 Mg-1.43 Cu-0.20 Zr-0.04 Sr was investigated via scanning electron microscopy observations, X-ray diffraction analysis, hardness tests, electrical conductivity tests, tensile tests, intergranular corrosion tests, and exfoliation corrosion tests. The effect of pre-recovery on the microstructure and mechanical properties of this aluminum alloy was also studied. The results show that the pre-recovery heat treatment releases deformation energy, inhibits recrystallization, and decreases the dislocation density. Although the pre-recovery heat treatment has little effect on the hardness, electrical conductivity, and elongation of this aluminum alloy, it can dramatically improve the alloy's tensile strength(the maximum tensile strength increased from 785.0 MPa to 809.2 MPa). Moreover, the tensile properties of this aluminum alloy have a certain degree of isotropy, and the pre-recovery heat treatment does not affect this property. In addition, the rolled aluminum alloy exhibits good corrosion resistance, but the effect of the pre-recovery heat treatment on the alloy's resistance to intergranular and exfoliation corrosion is negligible.

7xxx高强铝合金搅拌摩擦焊研究进展

针对7xxx高强铝合金的搅拌摩擦焊研究现状,主要从焊接缺陷、搅拌针形状的选择、接头软化、疲劳性能及耐蚀性等方面详述了7xxx高强铝合金焊接过程中存在的问题。对于7xxx高强铝合金的搅拌摩擦焊(FSW),焊接缺陷及焊缝成形质量差都会导致接头软化、疲劳寿命降低及耐蚀性变差等问题;优化FSW焊接工艺参数,减少焊接缺陷,改善焊缝成形质量,有利于降低接头软化程度、提高接头的疲劳寿命及耐蚀性;选择合适形状的搅拌针对7xxx高强铝合金进行FSW,有利于改善接头的力学性能;对FSW接头进行表面机械滚压处理和超声冲击处理,改善接头表面的应力状态,有利于改善接头的疲劳性能;对FSW接头进行适当的焊后热处理,改善接头中强化相的形态、分布状态及晶粒特征,有利于改善接头的耐蚀性。

7075与ER5356铝合金焊丝用于7075铝合金MIG焊接头性能对比研究

采用MIG焊的方式使用自制7075铝合金焊丝与市面购进的ER5356焊丝进行3mm厚7075铝合金对接焊,对比分析两种焊丝焊接接头的显微组织与力学性能。经过光学显微镜(OM)、X射线衍射(XRD)、扫描电镜(SEM)与能谱仪(EDS)结合室温拉伸与显微硬度测试,结果表明:两种接头焊缝组织均为枝晶网状组织,但由于合金元素含量与热导量增大,7075接头焊缝组织相对细小且枝晶特征更为明显。SEM和XRD检测分析得出,由于焊接时金属流动作用将部分母材合金元素带至焊缝,两者焊缝析出相均主要为η相(MgZn_(2))、S相(CuMgAl_(2))或T相(AlZnMgCu),同时存在Al_(13)Fe_(4)金属化合物。7075焊缝平均硬度为120HV,相较于5356焊缝更为优异;两者拉伸力学性能较为接近,断裂机制相同。