Analysis of bulging process of aluminum alloy by overlapping sheet metal and its formability

The influences of strength coefficient K, work hardening exponent n and thickness t of the overlapping sheet on bulging process are analyzed based on hardening material model. Also, bulging experiments are carried out by taking the aluminum alloy LF21 as formed sheet metal, and selecting overlapping sheet with different thicknesses and material properties, by which accuracy of the above analysis result is verified in the aspects of geometric shape, thickness distribution and limit bulging height. The results show that higher strength coefficient K, larger work hardening exponent n and proper thickness of the overlapping sheet are helpful to improve the formability and forming uniformity of formed sheet metal.

Effect of process parameters on the morphology of aluminum/copper alloy lap joints by red and blue hybrid laser welding

In order to overcome the problems of many pores,large deformation and unstable weld quality of traditional laser welded aluminumcopper alloy joints,a red-blue dual-beam laser source and a swinging laser were introduced for welding.T2 copper and 6063 aluminum thin plates were lap welded by coaxial dual-beam laser welding.The morphology of weld cross section was compared to explore the influence of process parameters on the formation of lap joints.The microstructure characteristics of the weld zone were observed and compared by optical microscope.The results show that the addition of laser beam swing can eliminate the internal pores of the weld.With the increase of the swing width,the weld depth decreases,and the weld width increases first and then decreases.The influence of welding speed on the weld cross section morphology is similar to that of swing width.With the increase of welding speed,the weld width increases first and then decreases,while the weld depth decreases all the time.This is because that the red laser is used as the main heat source to melt the base metals,with the increase of red laser power,the weld depth increases.As an auxiliary laser source,blue laser reduces the total energy consumption,consequently,the effective heat input increases and the spatter is restrained effectively.As a result,the increase of red laser power has an enhancement effect on the weld width and weld depth.When the swing width is 1.2 mm,the red laser power is 550 W,the blue laser power is 500 W,and the welding speed is 35 mm/s,the weld forming is the best.The lap joint of T2 copper and 6063 aluminum alloy thin plate can be connected stably with the hybrid of blue laser.The effect rules of laser beam swing on the weld formation were obtained,which improved the quality of the joints.

Semi-solid processing of aluminum and magnesium alloys:Status,opportunity,and challenge in China

Owing to its low cost,short process and low energy consumption,semi-solid processing(SSP)of aluminum(Al)and magnesium(Mg)alloys has been considered as a competitive approach to fabricate complicated components with excellent performance.Over the past decade,significant progress has been achieved in deeply understanding the SSP process,the microstructure and performance of the fabricated components in China.This paper starts with a retrospective overview of some common slurry preparation methods,followed by presenting the performance and the underlying mechanisms of SSP fabricated alloys.Then,the mainstream opinions on the microstructure evolution and rheological flow behavior of semi-solid slurry are discussed.Subsequently,the general situation and some recent examples of industrial applications of SSP are presented.Finally,special attention is paid to the unresolved issues and the future directions in SSP of Al and Mg alloys in China.

Non-dendritic structural 7075 aluminum alloy by liquidus cast and its semi-solid compression behavior

Fine, equiaxed, non dendritic structure needed by semi solid processing was obtained by liquidus cast, i.e. 7075 wrought aluminum alloy cast from liquidus temperature. The microstructures after heat treatment at different temperatures and time in the semi solid range were observed, and the compression deformation behavior at different temperatures (490～600 ℃) and strain rates (5×10 -3 ～5s -1 ) was investigated by means of Gleeble 1500 thermal mechanical simulator. The results show that the deformation resistance of the non dendritic structure attained by liquidus cast in semi solid is remarkably lower than that of conventional dendritic structure. The formability of non dendritic structure is better than that of dendritic structure.

Processing map and hot deformation behavior of squeeze cast 6082 aluminum alloy

The hot deformation behavior and microstructure evolution of 6082 aluminum alloy fabricated through squeeze casting(SC)under different pressures were studied.The alloy was subjected to hot compression tests and 3D hot processing maps were established.The microstructure evolution was studied by optical microscope(OM),scanning electron microscope(SEM),and electron backscattered diffraction(EBSD).It is found that more dynamic recrystallization(DRX)grains are generated during the deformation of the specimen fabricated under higher SC pressure.At high temperature the effect of SC pressure on microstructure evolution weakens due to the dissolution of second phase particles.In addition,uneven second phase particles in specimens fabricated under higher SC pressure compressed with low temperature and middle strain rate would result in flow localization instability.Finally,the optimum deformation conditions for the 6082 aluminum alloy fabricated by SC were obtained at the temperatures of 430−500℃ and the strain rates of 0.01−1 s^(−1).

EVOLUTION OF MICROSTRUCTURES AND HARDNESS DURING CONTINUOUS THERMO-MECHANICAL PROCESSING OF 6201 ALUMINUM ALLOY

Continuous thermo-mechanical processing (CTMP) of 6201 aluminum alloy was simulated on Gleeble-1500. The deformed specimens were analyzed by the observation of TEM and the measurement of hardness. It was shown that rapid solid solution and aging treatment can be effectively combined in one procedure by the strain induced during CTMP. The deformation temperature is ranging from 540* C to 300* C, the hardness increases directly before the 6th pass followed by a slight drop, the amount of precipitates increases with the holding time after deformation. Uniformly distributed and stabilized Mg2Si precipitates, as well as dislocation substructure can be observed on deformed specimens which have been subsequently held at 300℃ for 60 seconds.

Effect of Cr elimination on flow behavior and processing map of newly developed ECO-7175 aluminum alloy during hot compression

ECO-Al alloys are introduced as a game-changer for the aluminum industry and it is of utmost importance to determine the role of alloying elements in their processing characteristics.In this study,the effects of Cr on the hot deformation behavior of newly-developed ECO-7175 alloy were investigated.ECO-7175 samples with and without Cr were hot-compressed using a Gleeble simulator(temperature range of 350−500℃ and strain rates of 0.001−1 s^(−1)).The results were used to study the constitutive equations,the processing maps,and the microstructural evolution of the alloys.In Cr-containing alloy,the analysis of the deformation activation energy reveals that the rate-controlling mechanisms of the deformation change gradually from self-diffusion of Al(or diffusion of Mg in Al)to diffusion of Cr in Al by decreasing the Zener−Hollomon parameter.The analysis of the processing maps of Cr-containing alloy shows that the dynamic recrystallization(DRX)zone is limited to the deformation at high temperatures and low strain rates and expands with increasing applied strain.On the other hand,it is found that the self-diffusion of Al(or Mg in Al)is the only rate-controlling mechanism during hot deformation of Cr-free alloy in all processing conditions and its DRX zone is independent of the plastic strain.

Effect of processing way and aging treatment on properties and microstructures of 7B04 aluminum alloy

The influence of forging and aging treatment on mechanical properties and microstructure of large size prestretched thick plate of 7B04 aluminium alloy was investigated through tensile test, corrosion test, transmission electronic microcopy(TEM) and energy dispersive spectrum(EDS) analysis. The results show that the properties of plate performed extra forging (FSR technology) are much higher than those of plate without forging (CSR technology). T7451 temper is preferred to resisting corrosion than T651 temper due to a wide PFZ and discontinuous grain boundary precipitates.

Exploring material flow in friction stir welding using stacked structure of 2024 and 6061 aluminum alloys

An experimental technique based on stacked structures was developed to observe the material flow behavior of the friction stir welding （FSW） process. Analysis of section views along different directions revealed important new details of the material flow in FSW process. In this work, a general flow model of FSW was constructed based on the analysis of different static section views of stacked structure weld. The formation of onion rings was found to be a geometric effect due to layered deposition attd the extrusion occurred at the interface between flow arm （FA） and stirring zone （SZ）.

Material flow behavior and microstructural evolution during refill friction stir spot welding of alclad 2A12-T4 aluminum alloy

In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of alclad 2A12-T4 aluminum alloy during refill friction stir spot welding.There are two material flow components, i.e., the inward-or outward-directed spiral flow on the horizontal plane and the upward-or downward-directed flow on the vertical plane.In the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower layer.In the refill stage, this is process reversed.As such, there is no obvious vertical plasticized metal flow between adjacent layers.Welding leads to the coarsening of S(Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir zone.Continuous dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.

Tsinghua University Tsinghua-TOYO Research and Development Center of Magnesium and Aluminum Alloys Processing Technology

Tsinghua-TOYO Research and Development Center of Magnesium and Aluminum Alloys Processing Technology was officially established between Tsinghua University and TOYO Machinery & Metal Co. on Feb. 26, 2002, which is a non-independent legal research organization located in Department of Mechanical Engineering of Tsinghua University. The center was equipped with one set of 650t automatic magnesium and aluminum alloys diecasting machine and necessary accessories including the melting furnaces for magnesium alloys and aluminum alloys, an accurate magnesium pump to transfer the magnesium alloys to the shot sleeve of the die casting machine, a die temperature controller, and data logging systems for cavity pressure and die temperature distributions, etc. The center is aimed to the research and development of magnesium and aluminum die casting process and their related technologies, and the main research contents include:

Influence of material processing on crystallographic and electrochemical properties of cobalt-free LaNi_(4.95)Sn_(0.3) hydrogen storage alloy

The effects of the alloy preparation methods, including the conventional casting, annealing and melt-spinning, on the crystallographic and electrochemical properties of the Co-free LaNi4.95Sn0.3 alloy samples were investigated. The results reveal that the as-cast alloy consists of a main phase of CaCu5-type structure and a little second phase (Sn) with noticeable composition segregation and rather poor cycling stability (S200=40.1%). While the annealed and melt-spun alloys are of single CaCu5-type structure phase with a more homogeneous composition and lower cell volume expansion rate (?V/V) on hydriding, and a dramatically improved cyclic stability (S200=73.6%?76.2%), although their activation rate, initial capacity and high-rate dischargeability are lowered somewhat. It is found that the decrease in both the electrocatalytic activity and the hydrogen diffusion rate of the annealed and melt-spun alloys is the main cause for their relatively lower high-rate dischargeability, and the improved cycling stability is due to their lower volume expansion on hydriding and more uniform composition.

Effects of process parameters on mechanical properties and microstructures of creep aged 2124 aluminum alloy

A series of tests were carried microstructures of 2124 aluminum alloy in increase of aging time, temperature and low-to-peak-to-low manner. No significant out to investigate the effects of process parameters on mechanical properties and creep aging process. The results show that creep strain and creep rate increase with the applied stress. The hardness of specimen varies with aging time and stress in a effect of temperature on hardness of material is seen in the range of 185-195 ℃. The optimum mechanical properties are obtained at the conditions of （200 MPa, 185 ℃, 8 h） as the result of the coexistence of strengthening S＂ and S＇ phases in the matrix by transmission electron microscopy （TEM）. TEM observation shows that applied stress promotes the formation and growth of precioitates and no obvious stress orientation effect is observed in the matrix.

Material driven workability simulation by FEM including 3D processing maps for magnesium alloy

The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.

Characterization of hot deformation behavior of AA2014 forging aluminum alloy using processing map

The hot deformation behavior of AA2014forging aluminum alloy was investigated by isothermal compression tests attemperatures of350-480°C and strain rates of0.001-1s-1on a Gleeble-3180simulator.The corresponding microstructures of thealloys under different deformation conditions were studied using optical microscopy(OM),electron back scattered diffraction(EBSD)and transmission electron microscopy(TEM).The processing maps were constructed with strains of0.1,0.3,0.5and0.7.The results showed that the instability domain was more inclined to occur at strain rates higher than0.1s-1and manifested in theform of local non-uniform deformation.At the strain of0.7,the processing map showed two stability domains:domain I(350-430°C,0.005-0.1s-1)and domain II(450-480°C,0.001-0.05s-1).The predominant softening mechanisms in both of the twodomains were dynamic recovery.Uniform microstructures were obtained in domain I,and an extended recovery occurred in domainII,which would lead to the potential sub-grain boundaries progressively transforming into new high-angle grain boundaries.Theoptimum hot working parameters for the AA2014forging aluminum alloy were determined to be370-420°C and0.008-0.08s-1.

Significance-based optimization of processing parameters for thin-walled aluminum alloy tube NC bending with small bending radius

Thin-walled aluminum alloy tube numerical control （NC） bending with small bending radius is a complex process with multi-factor coupling effects and multi-die constraints. A significance-based optimization method of the parameters was proposed based on the finite element （FE） simulation, and the significance analysis of the processing parameters on the forming quality in terms of the maximum wall thinning ratio and the maximum cross section distortion degree was implemented using the fractional factorial design. The optimum value of the significant parameter, the clearance between the tube and the wiper die, was obtained, and the values of the other parameters, including the friction coefficients and the clearances between the tube and the dies, the mandrel extension length and the boost velocity were estimated. The results are applied to aluminum alloy tube NC bending d50 mm×1 mm×75 mm and d70 mm×1.5 mm×105 mm （initial tube outside diameter D0 × initial tube wall thickness t0 × bending radius R）, and qualified tubes are produced.

Influence of addition of Gr_p/Al_2O_(3p )with SiC_p on wear properties of aluminum alloy 6061-T6 hybrid composites via friction stir processing

Aluminum alloy base surface hybrid composites were fabricated by incorporating with mixture of （SiC＋Gr） and （SiC＋Al2O3） particles of 20 μm in average size on an aluminum alloy 6061-T6 plate using friction stir processing （FSP）. Microstructures of both the surface hybrid composites revealed that SiC, Gr and Al2O3 are uniformly dispersed in the nugget zone （NZ）. It was observed that the addition of Gr particles rather than Al2O3 particles with SiC particles, decreases the microhardness but immensely increases the dry sliding wear resistance of aluminum alloy 6061-T6 surface hybrid composite. The observed microhardness and wear properties are correlated with microstructures and worn micrographs.

High-strength and thermally stable TiB_(2)-modified Al-Mn-Mg-Er-Zr alloy fabricated via selective laser melting

To increase the processability and plasticity of the selective laser melting(SLM)fabricated Al-Mn-Mg-Er-Zr alloys,a novel TiB_(2)-modified Al-Mn-Mg-Er-Zr alloy with a mixture of Al-Mn-Mg-Er-Zr and nano-TiB_(2) powders was fabricated by SLM.The pro-cessability,microstructure,and mechanical properties of the alloy were systematically investigated by density measurement,microstruc-ture characterization,and mechanical properties testing.The alloys fabricated at 250 W displayed higher relative densities due to a uni-formly smooth top surface and appropriate laser energy input.The maximum relative density value of the alloy reached(99.7±0.1)%,demonstrating good processability.The alloy exhibited a duplex grain microstructure consisting of columnar regions primarily and equiaxed regions with TiB_(2),Al6Mn,and Al3Er phases distributed along the grain boundaries.After directly aging treatment at a high tem-perature of 400℃,the strength of the SLM-fabricated TiB_(2)/Al-Mn-Mg-Er-Zr alloy increased due to the precipitation of the secondary Al6Mn phases.The maximum yield strength and ultimate tensile strength of the aging alloy were measured to be(374±1)and(512±13)MPa,respectively.The SLM-fabricated TiB_(2)/Al-Mn-Mg-Er-Zr alloy demonstrates exceptional strength and thermal stability due to the synergistic effects of the inhibition of grain growth,the incorporation of TiB_(2) nanoparticles,and the precipitation of secondary Al6Mn nanoparticles.

Influence of multi-pass friction stir processing on microstructure and mechanical properties of 7B04-O Al alloy

Three-pass friction stir processing(FSP)with different moving distances of the stirring tool between the two successivepasses,50%diameter of the pin(traditional way)and50%diameter of the shoulder(novel way),was conducted on7B04-O Al alloy.The result shows that an improvement in the mechanical properties of the processed zone is accomplished due to grain and secondphase particles refinement.The hardness of the multi-pass FSP(M-FSP)sample is about HV40higher than that of the base metal.And the tensile strength of the M-FSP specimens is also significantly increased to about1.4times that of the base metal.Besides,theweak region of the processed zone is mainly dependent on the moving distance,where it is the previous pass stir zone in thetraditional way and the transitional zone in the novel way.Increasing the rotational speed narrows the weak region in the novel way,while it does not in the traditional way.

Induction reheating of A356.2 aluminum alloy and thixocasting as automobile component

The development work for producing an automobile component by thixocasting using A356.2 alloy was introduced.As the first step,the alloy was electromagnetically stirred and solidified to produce a billet with non-dendritic microstructure.The microstructure depended on several process parameters such as stirring intensity,stirring frequency,cooling rate,and melt initial superheat.Through a series of computational studies and controlled experiments,a set of process parameters were identified to produce the best microstructures.Reheating of a billet with non-dendritic microstructure to a semisolid temperature was the next step for thixo-casting of the components.The reheating process was characterized for various reheating cycles using a vertical-type reheating machine.The induction heating cycle was optimized to obtain a near-uniform temperature distribution in radial as well as axial direction of the billet,and the heating was continued until the liquid fraction reached about 50%.These parameters were determined with the help of a computational fluid dynamics(CFD) model of die filling and solidification of the semisolid alloy.The heated billets were subsequently thixo-cast into automobile components using a real-time controlled die casting machine.The results show that the castings are near net shape,free from porosity,good surface finish and have superior mechanical properties compared to those produced by conventional die casting processes using the same alloy.