Simulation of Dynamic Recrystallization in 7075 Aluminum Alloy Using Cellular Automaton

The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution in 7075 aluminum alloy during hot deformation.Isothermal compression tests were conducted to obtain material parameters for 7075 aluminum alloy,leading to the establishment of models for dislocation density,nucleation of recrystallized grains,and grain growth.Integrating these aspects with grain topological deformation,our CA model effectively predicts flow stress,dynamic recrystallization(DRX) volume fraction,and average grain size under diverse deformation conditions.A systematic comparison was made between electron back scattered diffraction(EBSD) maps and CA model simulated under different deformation temperatures(573 to 723 K),strain rates(0.001 to 1 s^(-1)),and strain amounts(30% to 70%).These analyses indicate that large strain,high temperature,and low strain rate facilitate dynamic recrystallization and grain refinement.The results from the CA model show good accuracy and predictive capability,with experimental error within 10%.

Mechanical properties of graphene nanoplatelets reinforced 7075 aluminum alloy composite fabricated by spark plasma sintering

A 0.3wt%graphene nanoplatelets(GNPs)reinforced 7075 aluminum alloy matrix(7075 Al)composite was fabricated by spark plasma sintering and its strength and wear resistance were investigated.The microstructures of the internal structure,the friction surface,and the wear debris were characterized by scanning electron microscopy,X-ray diffraction,and Raman spectroscopy.Compared with the original 7075 aluminum alloy,the hardness and elastic modulus of the 7075 Al/GNPs composite were found to have increased by 29%and 36%,respectively.The results of tribological experiments indicated that the composite also exhibited a lower wear rate than the original 7075 aluminum alloy.

Rheological behavior of semi-solid 7075 aluminum alloy at steady state

The further application of semi-solid processing lies in the in-depth fundamental study like rheological behavior. In this research, the apparent viscosity of the semi-solid slurry of 7075 alloy was measured using a Couette type viscometer. The effects of solid fraction and shearing rate on the apparent viscosity of this alloy were investigated under different processing conditions. It can be seen that the apparent viscosity increases with an increase in the solid fraction from 10% to 50%(temperature 620 oC to 630 oC) at steady state. When the solid fraction was fi xed, the apparent viscosity can be decreased by altering the shearing rate from 61.235 s-1 to 489.88 s-1 at steady state. An empirical equation that shows the effects of solid fraction and shearing rate on the apparent viscosity is fi tted:. The microstructure of quenched samples was examined to understand the alloy's rheological behavior.

Effect of homogenizing treatment on microstructure and conductivity of 7075 aluminum alloy prepared by low frequency electromagnetic casting

The heat treatment process has great effects on microstructure and conductivity of ingots. In this study, the ingots of high strength 7075 aluminum alloy were prepared by low frequency electromagnetic casting(LFEC), and the effect of different homogenization processes(single-step homogenization at 465 ℃ for different holding times and three-step homogenization) on the microstructure and conductivity of 7075 aluminum alloy were studied by means of metallographic microscopy, electrical conductivity test, differential thermal analysis and X-ray diffraction phase analysis. For comparison, the ingot by conventional direct casting(DC) under the same conditions was also prepared. Results show that the non-equilibrium eutectic phases with low melting point in the ingot dissolve continuously into the matrix as the holding time of single-step homogenization increases. The endothermic peak of non-equilibrium phases can not be completely eliminated through a 24 h single-step homogenization, but can be eliminated after a three-step homogenization(200 ℃/2 h + 460 ℃/6 h + 480 ℃/12 h). Meanwhile, the homogenization has a better effect on the LFEC ingot than the conventional DC ingot. Under the same homogenizing conditions, the grains of LFEC ingot are characterized by a lower content of low melting point phases and the ingot shows higher electrical conductivity than DC ingot.

Investigation on the plastic work-heat conversion coefficient of 7075-T651 aluminum alloy during an impact process based on infrared temperature measurement technology

The plastic work-heat conversion coefficient is one key parameter for studying the work-heat conversion under dynamic deformation of materials. To explore this coefficient of 7075-T651 aluminum alloy under dynamic compression, dynamic compression experiments using the Hopkinson bar under four groups of strain rates were conducted, and the temperature signals were measured by constructing a transient infrared temperature measurement system. According to stress versus strain data as well as the corresponding temperature data obtained through the experiments, the influences of the strain and the strain rate on the coefficient of plastic work converted to heat were analyzed.The experimental results show that the coefficient of plastic work converted to heat of 7075-T651 aluminum alloy is not a constant at the range of 0.85–1 and is closely related to the strain and the strain rate. The change of internal structure of material under high strain rate reduces its energy storage capacity, and makes almost all plastic work convert into heat.

Strength mismatch mechanism on friction stir welding joint of 7075 aluminum alloy

The precipitated phases in the WNZ,TMAZ,HAZ and BM of the friction stir welding(FSW)joint were observed using the transmission electron microscopy(TEM)and the lattice fringe spacing of the precipitated phases was measured.Combined with X-ray diffraction(XRD),the types of precipitated phases among the joint were confirmed and then the strength mismatch mechanism was revealed.The results show the precipitated phases of 7075 aluminum alloy FSW joint mainly consist of MgZn_(2),AlCuMg and Al_(2)CuMg.The microzone of the joint experienced different thermal cycles,the types and sizes of precipitated phases are different and the strengthening effect is different.The strengthening effect of the AlCuMg and Al_(2)CuMg are better than that of MgZn_(2).The precipitated phase in the WNZ mainly includes AlCuMg and Al_(2)CuMg,as well as the grain size is fine,the microhardness in this zone is pretty high.The number of precipitated phase AlCuMg and Al_(2)CuMg is smaller in the TMAZ and the MgZn_(2)is relatively more,which lead the microhardness decrease.The number of precipitated phase MgZn_(2)is relative larger in the HAZ,as well as the grain coarsening,the microhardness in this zone is lowest of the joint.At the same time,there are the precipitate free zones(PFZ)among the 7075 aluminum alloy FSW joint,which decreases the microhardness of the whole joint to some extent.

Effects of Aging Temperature on Microstructure and High Cycle Fatigue Performance of 7075 Aluminum Alloy

The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 190 ℃） for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing（150-190 ℃）, the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 ℃,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.

Microstructure and RRA Treatment of LFEC 7075 Aluminum Alloy Extruded Bars

The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting （LFEC） 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 ℃/24 h＋180 ℃/30 min＋120 ℃/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.

Properties and Structure of PEO Treated Aluminum Alloy

Plasma electrolytic oxidation(PEO)coatings were formed on 7075 aluminum alloy in silicate-borate based electrolyte with different duty cycles.The physical and chemical properties of the PEO coatings were thoroughly investigated.The wearing and corrosion properties of the coatings were evaluated by wearing experiments and potentiodynamic polarization tests,respectively.The results showed that the micro-hardness of the coatings first increased and then decreased with the increasing duty cycle.As a results,the wearing resistance of the coatings first increased and then decreased with the increasing duty cycle.Composition analysis proved that the coatings were mainly composed ofα-Al_(2)O_(3)andγ-Al_(2)O_(3).The presence of wear scars on the worn surface morphology demonstrates that the three-body rolling was the main wear mechanism for coated specimen.The corrosion study showed that the coating formed in the mixed electrolyte with duty cycle of 80%showed the most superior corrosion resistance.

Effect of die coating on surface crack depth of hot extruded 7075 aluminum alloy

The aluminum alloys belonging to the 7000 series are high-strength alloys used in a wide variety of products for weight reduction.They are primarily used in the field of transportation and aerospace.Among these,the A7075 alloy has the highest strength and is expected to be applicable in a wide range of fields,such as aircraft components and sports equipment.However,it has high deformation resistance and is prone to surface defects,which is called tearing.Tearing typically occurs at high temperatures and high ram speeds,and adversely affects productivity.The localized melting of Zn and additive compounds,due to the heat generated during the process,is considered to cause tearing.In this study,the effect of friction,heat,and tearing at the tool-metal interface was mitigated by improving the die surface quality.The reduced friction eliminated recrystallization by preventing the temperature from increasing to recrystallization temperature.In addition,an AlCrN coating was adopted instead of nitriding to improve the die surface quality.The tearing size and heat generated when using the AlCrN coating were found to be limited.Moreover,the grain size observed in the tearing region on the extruded surface was small.The simulations using the shear friction coefficient m observed from friction tests indicate that the use of the AlCrN coating improved the material flow.Thus,the AlCrN coating is considered effective for reducing friction at the interface and preventing the recrystallization of the extruded surface.From the aforementioned results,it can be inferred that a die coating can reduce the tearing sensitivity and increase the productivity of the A7075 alloy.

Processing map of as-cast 7075 aluminum alloy for hot working

The true stress-strain curves of as-cast 7075 aluminum alloy have been obtained by isothermal compression tests at temperatures of 300 500 ~C and strain rates of 0.01 10 s i. The plastic flow instability map is established based on Gegel B and Murthy instability criteria because the deformed compression samples suggest that the combination of the above two instability criteria has more comprehensive crack prediction ability. And the processing map based on Dynamic Mate- rial Model （DMM） of as-cast 7075 aluminum alloy has been developed through a superposition of the established instability map and power dissipation map. In terms of microstructure of the deformed samples and whether plastic flow is stable or not, the processing map can be divided into five areas： stable area with as-cast grain, stable area with homogeneous grain resulting from dynamic recovery, instability area with as-cast grain, instability area with the second phase and instability area with mixed grains. In consideration of microstructure characteristics in the above five areas of the processing map, the stable area with homogeneous grain resulting from dynamic recovery, namely the temperatures at 425465 ℃ and the strain rates at 0.01^-1 s^-1, is suggested to be suitable processing window for the as-cast 7075 aluminum alloy.

Preparation of bimodal grain size 7075 aviation aluminum alloys and their corrosion properties

The bimodal grain size metals show improved strength and ductility compared to traditional metals; however, their corrosion properties are unknown. In order to evaluate the corrosion properties of these metals, the bimodal grain size 7075 aviation aluminum alloys containing different ratios of coarse（100 μm in diameter） and fine（10 μm in diameter） grains were prepared by spark plasma sintering（SPS）. The effects of grain size as well as the mixture degree of coarse and fine grains on general corrosion were estimated by immersion tests, electrochemical measurements and complementary techniques such as scanning electron microscope（SEM） and transmission electron microscope-energy disperse spectroscopy（TEM-EDS）. The results show that, compared to fine grains, the coarse grains have a faster dissolution rate in acidic NaCl solution due to the bigger size,higher alloying elements content and larger area fraction of second phases in them. In coarse grains,the hydrogen ions have a faster reduction rate on cathodic second phases, therefore promoting the corrosion propagation. The mixture of coarse and fine grains also increases the electrochemical heterogeneity of alloys in micro-scale, and thus the increased mixture degree of these grains in metal matrix accelerates the corrosion rate of alloys in acidic NaCl solution.

Deep drawing of aluminum alloy 7075 using hot stamping

In this paper, simulations of deep drawing tests at elevated temperatures were carried out with experimental validation. The aim of this work was to study the effect of process parameters on formability and mechanical properties of aluminum alloy 7075 in hot stamping process.Process parameters, including blank temperature, stamping speed, blank holder force and friction coefficient, were studied. Stamping tests were conducted at temperatures between 350 and 500 ℃, blank holder force between 0 and 10 kN, stamping speed between 50 and 150 mm·s^-1, and friction coefficient between 0.1 and 0.3. Based on the analysis, it is shown that thickness homogeneity could be improved when the blank is formed at lower temperature,lower blank holder force and lower friction coefficient.Formability could be improved when the blank was well lubricated at about 400 ℃. Formability at stamping speed 50 mm·s^-1 is far better than those at other speeds. The mechanical property analysis shows that the hot stamping process could make the formed part to obtain high quality.

Effect of Temperature on Material Transfer Behavior at Different Stages of Friction Stir Welded 7075-T6 Aluminum Alloy

In this work, the morphologies of weld of 7075-T6 aluminum alloy via friction stir welding （FSW） were analyzed by optical microscopy, the temperature field was attained by numerical simulation, and the effect of temperature on material transfer behavior in the thermal-mechanical affected zone （TMAZ） at different stages was mainly investigated. The FSW process consists of three stages. It is very interesting to find that the maximum transfer displacement of material appears at the final stage of welding process, then at the stable stage and at the initial stage, which results from the difference of peak temperatures at different stages. At any stage, the material in TMAZ near the surface of weld transfers downwards, the material in the middle of weld moves upwards and the material near the bottom of weld hardly moves. In any cross section of weld, the largest transfer displacement of material appears in the middle of weld. The increase of rotational velocity and the decrease of welding speed are both beneficial to the transfer displacement of material in the middle of weld.

Formation of spheroidal microstructure in semi-solid state and thixoforming of 7075 high strength aluminum alloy

The effects of isothermal holding process on the microstructure evolution of semi-solid 7075 strength aluminum alloy produced by the recrystallisation and partial remelting(RAP) process were investigated. Tensile mechanical properties of as-received and thixoformed alloys at room temperature were examined. The results show that the microstructure of as-received alloy exhibits remarkable orientation along the deformation direction.With the increase of isothermal holding time, the solid particle grain size continuously increases and the degree of spheroidization also improves. Coalescence mechanism is dominant when reheated at 595 °C and Ostwald ripening mechanism is dominant when reheated at 615 °C in the semi-solid state. A lower coarsening rate is observed for 615 °C(coarsening rate K = 391 μm3 s-1) compared with the coarsening rate for 595 °C(coarsening rate K = 501 μm3 s-1). The RAP 7075 aluminum alloy can be successfully thixoformed and the filling of components is good after thixoforming. The thixoformed components exhibit favorite mechanical properties.

Microstructure and mechanical properties of low frequency electromagnetic casting 7075 aluminum alloy

This work explores the microstructure of low frequency electromagnetic casting （LFEC） 7075 aluminum alloys and investigates the effect of heat treatment process on its mechanical properties via the mechanical properties test, X-ray diffraction and transmission electron microscopy. It was found that the grains of LFEC ingot were finer and more evenly distributed than that of the conventional direct chill cast （DC） ingots. The microstructure of LFEC ingot extruded kept their original as-cast struc- ture with small and fine grains. With the same extrusion ratio, the average grain diameters of LFEC and conventional DC extruded were about 10 and 20 #m, re- spectively. LFEC extruded also had a better aging property, since the regime of T6 treatment peak value aging was at 120 ~C for 24 h, the tensile strength and hardness （HV） of the LFEC extruded were 673.50 MPa and 194.62, respectively, which were all higher than those of the conventional DC extruded, indicating that the process regime can be applied in the industrial production.

Si-Assisted Solidification Path and Microstructure Control of 7075 Aluminum Alloy with Improved Mechanical Properties by Selective Laser Melting

The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical issue, in this study, Si is employed to assist the SLM printing of high-strength Al7075. The laser energy density during SLM is optimized, and the eff ects of Si element on solidification path, relative density, microstructure and mechanical properties of Al7075 alloy are studied systematically. With the modified solidification path, laser energy density, and the dense microstructure with refined grain size and semi-continuous precipitates network at grain boundaries, which consists of fine Si, β-MgSi, Q-phase and θ-AlCu, the hot cracking phenomenon and mechanical properties are eff ectively improved. As a result, the tensile strength of the SLM-processed Si-modified Al7075 can reach 486 ± 3 MPa, with a high relative density of ~ 99.4%, a yield strength of 291 ± 8 MPa, fracture elongation of(6.4 ± 0.4)% and hardness of 162 ± 2(HV) at the laser energy density of 112.5 J/mm~3. The main strengthening mechanism with Si modification is demonstrated to be the synergetic enhancement of grain refinement, solution strengthening, load transfer, and dislocation strengthening. This work will inspire more new design of high-strength alloys through SLM.