Effects of process parameters on electromagnetic forming of AZ31 magnesium alloy sheets at room temperature

In this work, the effects of process parameters on AZ31 magnesium alloy sheets were investigated by electromagnetic bulging experiments. The bulging height increases with increasing discharging energy, which is adjusted by tuning discharge voltage and capacitance. The limit dome height of electromagnetic forming is markedly improved as compared to quasi-static forming. In order to improve the efficiency of the energy, 0.5- and 1-mm thick Al driver sheet were used to accelerate the magnesium alloy sheets. For rupturing the AZ31 sheet, the discharging energy can be reduced from a maximum value of 4.356 kJ (no driver) to 2.304 kJ (with1-mm Al driver sheet). The numerical simulation for the electromagnetic forming of AZ31 sheet is performed by means of ANSYS FEA software. The change of velocity, strain rate, and plastic strain energy were analyzed by simulation. Compared with quasi-static forming limit results, increases in the major and minor principal strains of approximately 68 and 72 % were achieved, respectively.     

Optimization of springback for AZ31 magnesium alloy sheets in the L-bending process based on the Taguchi method

Springback is a primary issue which is encountered during most sheet metal bending processes. Using the Taguchi method, this study investigates the springback of L-bending with a step in the die through simulation and experiments for AZ31 magnesium alloy sheets at different temperatures. The process parameters for bending springback in this study include: lower punch radius, die clearance, step height, and step distance; we use a Taguchi L9 orthogonal array to design the combinations for the experiments. The results of ANOVA analysis show that, for each bending temperature, the process parameters that affect springback occur in the following order: step height (greatest), lower punch radius (next), die clearance (smaller), and step distance (smallest). In addition, with the increase of the bending temperature, the angle of springback decreases. The optimal parameter combinations at each bending temperature from the signal-to-noise response are all the same, namely, a die radius of 2?mm, die clearance of 0.5?mm, step height of 0.1?mm, and step distance of 2?mm. When the bending temperatures are 100°C, 150°C, and 200°C, the angles after springback of the optimal experimental parameter combination are 91.06°, 90.63°, and 89.84°, respectively.     

Effects of driver sheet on magnetic pulse forming of AZ31 magnesium alloy sheets

In this work, the formability of AZ31 magnesium alloy sheets was investigated by electromagnetic bulging experiments with driver sheet. Al (0.5 mm, 1 mm, and 2 mm thick) and Cu (1 mm thick) driver sheets were used to accelerate the AZ31 sheet in electromagnetic forming (viz magnetic pulse forming) process. In order to evaluate the effect of impact induced by driver sheet, the electromagnetic bulging experiments with gap between AZ31 sheet and driver sheet were investigated. Compared with quasi-static forming limit results, increases in the major and minor principal strains (with 0.5 mm, 1 mm driver sheet, and without driver sheet) of approximately 68 % and 72 % were achieved, respectively. However, the major and minor principal strains with 2 mm Al driver sheet increased about 148 % and 184 %. When the energy is up to 2.788 kJ after the first crack (with 1 mm Al driver sheet) producing, the major and minor strains increase about four times compared to the quasi-static condition.     

Failure modes during uniaxial deformation of magnesium alloy AZ31B tubes

This study examines magnesium alloy AZ31B circular tubing subject to uniaxial compressive loading and compares their performance to steel (ASTM A106 Grade B) and aluminium alloy AA6061T6 circular tubing at both low and high strain rates. Quasi-static tests were undertaken using a hydraulic testing machine for a range of tube lengths and thicknesses for tubes with an outside diameter of approximately 48 mm. To examine the effects of higher strain rate, a drop test rig was used. It was found that magnesium alloy AZ31B outperforms both the steel and aluminium alloys in terms of energy absorption for equivalent mass when subject to uniaxial compressive loads for the thicker sections. This is further enhanced by alloy AZ31B’s strain rate sensitivity, as there is a dramatic increase in the energy absorption at higher strain rates. However, the AZ31B tubes usually fail by fracturing, which generally involves a shear fracture mode, unlike the aluminium and steel tubes, which generally retained their structural integrity to a higher degree. The greatest energy absorption was obtained when the AZ31B failed via fine sharding. This failure mode appeared to be related to the presence of micro-cracks on the surface of the section obtained by overheating during extrusion. At higher strain rates, much greater plasticity and compaction are present in the fracture modes for the thicker AZ31B tubing. Some of the fracture modes have been discussed and the failure/fracture modes are compared with a typical aluminium alloy tube failure mode classification chart.     

AZ31镁合金热轧制工艺及数值模拟研究

针对AZ31镁合金平板的轧制过程进行试验研究,通过控制温度及不同道次的压下率等工艺条件,最终将36mm厚的镁合金铸锭,压制成厚度为1mm的板材.同时运用MSC.Marc软件,采用显式弹塑性有限元法对AZ31镁合金平板的轧制过程进行热-机耦合三维数值模拟.对轧件在轧制过程的金属流动、温度、应力及应变分布等特点进行分析,并与实际试验结果进行对比,验证了模拟结果的准确性.     

Analysis of the bulging process of an AZ31B magnesium alloy sheet with a uniform pressure coil

As the lightest metal material, magnesium alloy is widely used in the aerospace, automobile, and consumer electronic industries. However, magnesium alloy sheet has poor formability at room temperature. Electromagnetic forming is a high velocity forming technique that can promote the formability of low ductility materials, improve the strain distribution of workpieces, and reduce their wrinkling and springback. In this work, a uniform pressure coil was used to bulge AZ31B magnesium alloy sheets. The finite element method was then used to analyze this bulging process. The bulging contours and displacements of AZ31B magnesium alloy sheets were consistent with the experiment results. The distribution of the magnetic field intensity and magnetic field forces were found to be better than using a flat spiral coil. The deformation rule of AZ31B magnesium alloy sheet using the uniform pressure coil differed from that using the flat spiral coil. The largest strain occurred at the center of the sheet.     

Evaluation of the strain behaviour of butt joints on AZ31 magnesium alloy thin sheets welded by Nd:YAG laser

In this work, the mechanical and technological behaviour of AZ31 magnesium alloy laser welded joints is investigated. The forming behaviour of the joints is analysed by both tensile and biaxial stretch tests. Each test is monitored using a digital image correlation system in order to acquire the complete strain field during the whole test. Both in tensile and biaxial stretching tests, the strain maps reveal that the weld bead makes the strain path experienced by the welded specimen more critical than the one experienced by the base material, and this can be related to morphological defects of the weld bead.     

AZ31B镁合金表面激光合金化Al-SiC涂层制备及其性能研究

针对镁合金表面耐磨性差,采用预置粉末法对AZ31B表面进行激光合金化Al-SiC粉末实验。使用光学显微镜和扫描电子显微镜(SEM)、能谱分析仪(EDS)、摩擦磨损试验机、显微硬度计对合金化涂层的微结构、相组成及性能进行了分析研究。结果表明,强化层与基体呈冶金结合、组织均匀致密;合金化层主要由Mg17Al12、SiC、Mg2Si、Al4C5、Al2O3等相组成。涂层的显微硬度、耐磨损性能都明显高于基体。     

Tribology characteristics of magnesium alloy AZ31B and its composites

In this paper, wear characteristics of magnesium alloy, AZ31B, and its nano-composites, AZ31B/nano-Al₂O_3, processed by the disintegrated melt deposition technique are investigated. The experiments were carried out using a pin-on-disk configuration against a steel disk counterface under different sliding speeds of 1, 3, 5, 7 and 10 m/s for 10 N normal load, and 1, 3 and 5 m/s for 30 N normal load. The worn samples and wear debris were then examined under a field emission scanning electron microscopy equipped with an energy dispersive spectrometer to reveal its wear features. The wear test results show that the wear rates of the composites are gradually reduced over the sliding speed range for both normal loads. The composite wear rates are higher than that of the alloy at low speeds and lower when sliding speed further increased. The coefficient of friction results of both the alloy and composites are in the range of 0.25–0.45 and reaches minimums at 5 m/s under 10 N and 3 m/s under 30 N load. Microstructural characterization results established different dominant mechanisms at different sliding speeds, namely, abrasion, delamination, oxidation, adhesion and thermal softening and melting. An experimental wear map was then constructed.     

Numerical study of the flange earring of deep-drawing sheets with stronger anisotropy

A Barlat–Lian anisotropy yield function is introduced into a quasi-flow corner theory of elastic–plastic finite deformation and the elastic–plastic large deformation finite element formulation based on the principle of virtual velocity and the discrete Kirchhoff triangle plate shell element model. The focus of the present researches is on the numerical simulation of the flange earring of deep-drawing process of circular sheets with stronger anisotropy, based on which, the schemes for controlling the flange earring are proposed.     

A finite element analysis of rigid-plastic deformation of the flange in a deep-drawing process based on a fourth-degree yield function

A general formulation for finite element analyses of very large rigid-plastic deformation is given by introducing a local system of convected co-ordinates into each element and taking the rotation of the principal axes of orthotropy of the material into consideration with respect to the two cases: (1) the case where the equivalent strain-rate is given by a function of strain-rate components and (2) the case where is defined by the formula , where σ_ij are stress components and gs is the equivalent stress. example, large deformation of the flange region in a deep-drawing process of a circular orthotropic metal sheet is analyzed on the basis of the conventional quadratic yield function and a fourth-degree one. The result shows that the effect of the axis rotation suppresses the ear-development to a certain extent, that any explicit expression of in terms of is not necessarily required for calculation and the definition suffices for the purpose, that the fourth-degree yield function gives us the shape of the deformed flange in good agreement with the experiment in contrast with the quadratic one which gives a too excessive ear-development, and so forth.     

Modeling the material behavior of magnesium alloy AZ31 using different yield criteria

Nowadays, the finite element analysis (FEA) is playing a main rule in fields of sheet metal forming for designing processes and dimensioning parts. The most frequent yield criteria used in the FE commercial programs for the sheet-metal-forming simulation, like AUTOFORM, PAMSTAMP, etc., are Hill’48 for common steels or Barlat’89 and various BBC models for some aluminum alloys. In this paper, different yield loci for biaxial tensile stress conditions of the magnesium sheet metal alloy AZ31 are investigated. The experimental investigations have been done using the specimen geometry for the experimental setup developed at the Chair of Manufacturing Technology (LFT) of the University of Erlangen. The yielding behavior is determined basing exclusively on real material data out of experiments so that no FE calculations are necessary to detect strains and stresses. Using these data, several yield criteria are applied to approximate the real material characteristics, whereas the model of BBC’2005 leads to the best agreement for uniaxial yield stresses, the anisotropy coefficients, and the yield locus.     

Free vibration analysis of a thin rectangular plate with multiple circular and rectangular cut-outs

The present work is to investigate the variation in the natural frequency of a rectangular plate with the change in position of cut outs of different sizes along its diagonal and major axis line by considering different aspect ratios of plates. In this regard the free vibration analysis of an isotropic rectangular plate of various aspect ratios with different sizes of multiple circular and rectangular cut-outs is carried out by using an Independent coordinate coupling method (ICCM) under simply supported boundary condition. The ICCM utilizes independent coordinates separately for plate domain and hole domain, in which the reduced mass and stiffness matrices can be derived, by matching the deflection conditions for each hole imposed on the expressions. The resulting equation is useful for the calculation of the Eigen values. The position, size, and number of cutouts have been varied in all the possible ways to investigate their effects on the natural frequency of the rectangular plate.     

The dynamic deformation of a circular membrane

The stereophotogrammetric method, adapted to the measurement of displacements, strains and strain rates during the deformation process in a circular membrane, is presented in this article. In this process the circular membrane is subjected to an abrupt pressure by the underwater detonation of explosive. This method is based on photographing the course of the membrane deformation. The photographs are taken with a high-speed film camera, equipped with a stereoscopic attachment. Stereoscopic photographs, made with steady frequency, are thus obtained. The constant frequency allows the determination of the cylindrical co-ordinates r(, t) and y(,t) of specific points of the membrane at the time of the deformation process. The results obtained have been presented graphically.     

A finite element analysis of the rigid-plastic deformation of the flange in a deep-drawing process based on a fourth-degree yield function—II

Deformation of the flange in the cylindrical cup drawing process is analysed by the newley-designed hybrid rigid-plastic finite element method on the basis of a fourth-degree yield function f for orthotropy, and the results are compared with those based on the traditional quadratic yield function g and the experiments. The accuracy and the efficiency of the adopted method, the computability of accurate ear-development up to 8-ears by the use of f, the deficiencies in g, relationship between the ear configuration and the planar distribution of r-value and uniaxial yield stress, the factors influencing on the circumferential distribution of drawing force, the effects of various material properties on the degree of ear-development and so forth are demonstrated.     

Tribological properties of the AZ91D magnesium alloy hardened with silicon carbide and by severe plastic deformation

Results of investigation of the tribological contact characteristics of R18 tool steel in interface with AZ91D magnesium alloy hardened with SiC disperse powder filler and by severe plastic deformation (SPD)—specifically, equal-channel angular pressing (ECAP)—are presented. It is established that introduction of the SiC powder filler into the magnesium alloy increases the friction coefficient and reduces the wear rate. The size and volume of the powder filler particles, the normal load, and the relative sliding velocity influence these tribological characteristics. SPD of the original material leads to reduction of the molecular component of the friction coefficient.