Study on Dynamic Mechanical Behavior of Al-Mg-Si Alloy

The dynamic mechanical behavior of Al-Mg-Si alloy was investigated under different strain rates by mechanical property and microstructure characterization,constitutive behavior analysis and numerical simulation in the present study.As the strain rate increases,the yield strength,ultimate tensile strength and elongation increase first,then remain almost constant,and finally increase.The alloy always exhibits a typical ductile fracture mode,not depending on the strain rate.However,as the strain rate increases,the number of dimples gradually increases.Tensile deformation can refine grains,however,the grain structure is slightly affected by the strain rate.An optimized Johnson-Cook constitutive equation was used to describe the mechanical behavior and obtained by fitting the true stress-strain curves.The parameter C was described by a function related to the strain rate.The fitting true stress-strain curves by the JC model agree very well with the experimental true stress-strain curves.The true stress-strain curves calculated by the finite element numerical simulation agree well with the experimental true stress-strain curves.

Preheating-assisted solid-state friction stir repair of Al-Mg-Si alloy plate at different rotational speeds

Additive friction stir deposition(AFSD)is a novel structural repair and manufacturing technology has become a research hotspot at home and abroad in the past five years.In this work,the microstructural evolution and mechanical performance of the Al-Mg-Si alloy plate repaired by the preheating-assisted AFSD process were investigated.To evaluate the tool rotation speed and substrate preheating for repair quality,the AFSD technique was used to additively repair 5 mm depth blind holes on 6061 aluminum alloy substrates.The results showed that preheat-assisted AFSD repair significantly improved joint bonding and joint strength compared to the control non-preheat substrate condition.Moreover,increasing rotation speed was also beneficial to improve the metallurgical bonding of the interface and avoid volume defects.Under preheating conditions,the UTS and elongation were positively correlated with rotation speed.Under the process parameters of preheated substrate and tool rotation speed of 1000 r/min,defect-free specimens could be obtained accompanied by tensile fracture occurring in the substrate rather than the repaired zone.The UTS and elongation reached the maximum values of 164.2MPa and 13.4%,which are equivalent to 99.4%and 140%of the heated substrate,respectively.

Microstructure evolution and precipitation behavior of Al-Mg-Si alloy during initial aging

The microstructure evolution and precipitation behavior of Al-Mg-Si alloy during initial aging were studied using hardness testing, conductivity testing, differential scanning calorimetry(DSC), and high resolution transmission electron microscopy(HRTEM). The results show that the precipitation sequence of the Al-Mg-Si alloy during initial aging can be represented as: supersaturated solid solution → spherical Mg/Si clusters → needle-like Guinier Preston(GP) zone → β″. Clusters are completely coherent with the Al matrix. The GP zone with relatively complete independent lattice parameters that differ slightly from the Al matrix parameters, is oriented along the direction of <111>Aland lying on {111}Alplane. The strength of the Al-Mg-Si alloy is greatly enhanced by the threedimensional strain field that exists between the β″ phase and the two {200}Alplanes. After aging at 170 ℃ for 6 h, the hardness reaches the peak of 127 HV and remains for a long time. At this stage, the electrical conductivity keeps relatively stable due to the formation of coherent precipitates(Mg/Si clusters/GP zones) and the reduction in solute atom concentration in the Al matrix. The severe coarsening and decreased number density of the β″ phase during the over-aging stage result in a significant decrease in the hardness.

Corrosion mechanism associated with Mg_2Si and Si particles in Al-Mg-Si alloys

The electrochemical behaviors and coupling behaviors of the Mg2Si and Si phases with α（Al） were investigated, the corrosion morphologies of Al alloys containing Mg2Si and Si particles were observed, and the corrosion mechanism associated with them in Al-Mg-Si alloys was advanced. The results show that Si particle is always cathodic to the alloy base, Mg2Si is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Mg and the enrichment of Si make Mg2Si transform to cathode from anode, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery at a later stage. As the mole ratio of Mg to Si in an Al-Mg-Si alloy is less than 1.73, it contains Mg2Si and Si particles simultaneously in the grain boundary area, and corrosion initiates on the Mg2Si surface and the precipitate-free zone （PFZ） at the adjacent periphery of Si particle. As corrosion time is extended, Si particle leads to severe anodic dissolution and corrosion of the PFZ at its adjacent periphery, expedites the polarity transformation between Mg2Si and the PFZ and accelerates the corrosion of PFZ at the adjacent periphery of Mg2Si particle.

Effects of high temperature pre-straining on natural aging and bake hardening response of Al-Mg-Si alloys

The influences of high temperature pre-straining (HT-PS) on the natural aging and bake hardening of Al?Mg?Si alloys were investigated by Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterization. The results show that pre-straining at 170 °C immediately after quenching can effectively resolve the rather high T4 temper hardness caused by the conventional room temperature (RT) pre-straining treatment, and give a better bake hardening response (BHR) after paint-bake cycle. HT-PS 7% at 170 °C for 10 min is chosen as the optimum process as it provides lower T4 temper hardness and better BHR. The simultaneous introduction of dislocations and Cluster (2) can significantly suppress the natural aging and promote the precipitation of β″ phase, and reduce the effects of deformation hardening by dynamic recovery.

Combined effect of deformation and artificial aging on mechanical properties of Al-Mg-Si Alloy

The effect of pre-deformation followed by or together with artificial aging on the mechanical properties as strength and ductility of an AA6060 aluminium alloy was studied. AA6060 was initially cast, homogenized and extruded according to standard industrial practice. The extruded material was then subjected to a solution heat treatment and subsequently artificial aging after （sequential mode） and during （simultaneous mode） various combinations of deformation （0-10%） and heat treatments. The aging behaviour and mechanical properties were characterized in terms of Vickers hardness and tensile testing. It is found that precipitation kinetics and associated mechanical response, in terms of hardness and tensile properties are strongly affected by pre-deformations. In terms of aging behaviour, kinetics is accelerated and the peak strength generally increases. Comparing sequential mode and simultaneous mode, the latter seems to give overall better mechanical properties and after considerably shorter aging times. The results of the two modes of pre-deformation are compared and discussed in view of differences in processing conditions and microstructure characteristics.

Influence of different solution methods on microstructure, precipitation behavior and mechanical properties of Al-Mg-Si alloy

The effects of different solution methods on microstructure, mechanical properties and precipitation behavior of Al-Mg-Si alloy were investigated by scanning electron microscope, transmission electron microscope, tensile test, and differential scanning calorimetry. The results revealed that the recrystallized grains of the alloy after the solution treatment with hot air became smaller and more uniform, compared with solution treatment with electrical resistance. The texture of the alloy after two solution treatment methods was different. More rotated cube components were formed through solution treatment with electrical resistance, which was better for improving the drawability of the alloy. The strength of the alloy under the solution treatment with hot air was higher before stamping, because of the small uniform grains and many clusters in the matrix. The alloy solution treated with hot air also possessed good bake hardenability, because the transformation occurred on more clusters in the matrix.

Effect of isothermal compression and subsequent heat treatment on grain structures evolution of Al-Mg-Si alloy

The constitutive relationships of Al-Mg-Si alloy deformed at various strain rates,temperatures and strains were studied.The microstructure evolution was quantitatively characterized and analyzed,including recrystallization fraction,grain sizes,local misorientation,geometrically necessary dislocation and stored strain energy during hot deformation and subsequent heat treatment.The results show that the dislocation density and energy storage are linear with ln Z during hot deformation and subsequent heat treatment,indicating continuous recrystallization occurring in both processes.With higher ln Z,the dislocation density declines more sharply during subsequent heat treatment.When ln Z is less than 28,dislocation density becomes more stable with less reduction during subsequent heat treatment after hot deformation.As these dislocations distribute along low angle grain boundaries,the subgrain has good stability during subsequent heat treatment.The main recrystallization mechanism during hot deformation is continuous dynamic recrystallization,accompanied by geometric dynamic recrystallization at higher ln Z.

Characterizations of precipitation behavior of Al-Mg-Si alloys under different heat treatments

The solidification-precipitation behavior of Al-Mg-Si multicomponent alloys has long been an absorbing topic. Experiments were carried out to analyze the precipitation behaviors of Al-Mg-Si alloys under different heat treatments. All specimens were homogenized at 570 ℃ for 8 h, and then solution treated at 540 ℃ for 55 min. Subsequently, the specimens were age treated for different times at temperatures of 100 ℃, 150 ℃ and 180 ℃, respectively. The experimental results show that the occurrence of dispersed free zones （DFZ） is caused by the uneven distribution of dispersed phase. During the aging process, pre-β＂ phases form at the initial stage and an aging temperature of 100 ℃is too low to complete the transformation of pre-β＂ to β＂. At 150℃, the precipitation sequence is concluded as SSSS-pre-β＂-pre-β＂＋β＂-β＂-β＇-β. Moreover, changes in sizes and densities of the pre-β＂, β＂and β＇ phases during the aging process has an important influence on the evolution of microhardness and electrical resistivity. The microhardness peak value of 150 ℃ is similar to that of 180 ℃, which is -141 HV. While, at 100℃, the microhardness increases slowly, and the attainable value is 127 HV up to 19 days. When the aging temperature is 100 ℃, the electrical resistivity has the highest average value. When the aging temperature exceeds 100 ℃, with the occurrence and growth of β＂and β＇, the resistivity has a distinct decrease with prolonged aging time.

Quantitative analysis of influence of α-Al(MnFeCr)Si dispersoids on hot deformation and microstructural evolution of Al-Mg-Si alloys

The microstructural evolution of AA6061 and Mn-bearing Al-Mg-Si-Cu alloys was studied by compression tests that were carried out between 300 and 500 °C with a wide range of strain rates. Compared to the AA6061 alloy, the large amount of α-Al(MnFeCr)Si dispersoids in the Mn-bearing alloy yielded a significant increase in the flow stress under all deformation conditions. The effects of the deformation parameters on the evolution of the microstructure were studied using electronic backscatter diffraction measurements. The predominant softening mechanism of both alloys was dynamic recovery. The presence of α dispersoids in Mn-bearing alloys effectively refined the size of substructures with misorientation angles in the range of 2°-5°, which retarded the dynamic recovery. To predict the subgrain size under various deformation conditions, the threshold stresses that were caused by α dispersoids were calculated by the modified Orowan equation and incorporated into a conventional constitutive equation. The subgrain size that was predicted by the modified constitutive equation showed satisfactory agreement with the experimental measurements.

Effects of dynamic cooling pre-aging treatment on mechanical properties and paint-bake hardening behavior of Al-Mg-Si alloy automotive sheets

In the industrial production, the dynamic cooling pre-aging treatment was employed to replace the isothermal pre-aging during the continuous heat treatment production of Al-Mg-Si alloy automotive sheets. The effects of dynamic cooling pre-aging treatment on mechanical properties and paint-bake hardening behavior of an Al-Mg-Si alloy sheet are proposed in this study. The scanning electron microscopy, transmission electron microscopy, tensile test, Vickers hardness test, and differential scanning calorimetry were conducted for the purpose. It was found that the dynamic cooling pre-aging treatment at low temperature region led to the decreasing of cluster II, resulting in the deterioration of the ability of the paint-bake hardening. With the increase of the cooling pre-aging temperature, the increasing of cluster II effectively improved the stability against natural aging and the paint-bake hardening ability. The optimized dynamic cooling pre-aging temperature was ~150 ℃. In this condition, the hardness increase of the alloy sheet with pre-aging treatment is low during storage at room temperature. The high yield strength increment is obtained after paint-bake hardening.

Effect of Equal Channel Angular Extrusion on the Microstructures and Properties of Two Extruded Al-Mg-Si Alloys

The effect of equal channel angular extrusion （ECAE） on the microstructure of two Al-Mg-Si extrusion alloys was investigated by high resolution electron backscattered diffraction （EBSD） using a field emission gun scanning electron microscope （FEG-SEM） and a transmission electron microscope （TEM）. Two contrasting alloys： a dilute alloy, based on alloy 6061 and a concentrated alloy, based on alloy 6069 were employed for this research. It has been found that prior ECAE to extrusion promotes high angle grain boundaries （HAGBs） in the extrusions, and the increase in HAGBs ratio is due to the large shear deformation involved in the process of ECAE. Tensile testing results show that a further ageing treatment strengthens the alloys after extrusion and the ECAE processed extrusions are more ductile than conventional extrusions.

Effect of copper on precipitation and baking hardening behavior of Al-Mg-Si alloys

The effects of copper on the ageing precipitation behavior of as-quenched and pre-aged AA6016 aluminum alloy were studied by differential scanning calorimetry （DSC）, Vickers hardness measurement and transmission electronic microscopy （TEM）. The results indicate that the addition of copper facilitates the growth of clusters （GP I） to the critical size during pre-ageing. Therefore, the addition of copper accelerates the transition from GP I （pre-β＂） to GP II （β＂） during final artificial ageing, and finally results in the favorable paint-bake response. However, the one with the copper level of 0.3% does not show significant baking hardening response as expected. Pre-aging can also reduce the detrimental effect due to natural aging of copper-containing alloys.

Effect of Zr Addition on Resistance to High Temperature Softening and Resistivity of 6082 Al-Mg-Si Alloys

The influence of zirconium on the resistance to high temperature softening of 6082 Al-Mg-Si alloys has been researched. The softening process of 6082 alloys with Zr and without Zr, isothermally conditioned at 250°C, has been investigated. The results show the inclusion of Zr inhibits the decrease of HB in hardness(HB) compared with the alloys without Zr. This is due to the Zr and Al forming coherent dispersoid-A!3Zr, and Al3Zr particles within an Al matrix, which effectively restricts grain boundary movement. A study is also carried out to investigate the changes in resistivity, which occurs during the ageing of alloys containing Zr, compared to those without Zr. It is found that in both cases there is an initial rapid rise in resistivity followed by a slower rise in resistivity as ageing proceeds. The value of resistivity is lower for 6082 alloys with Zr compared with 6082 alloys without Zr; this is explained in terms of the role of Zr in the 6082 alloys.

Electrochemical characteristics of Al-Mg and Al-Mg-Si alloy in sea water

Among Al alloys,particularly 5000 series Al Mg and 6000 series Al Mg Si often used as marine materials have excellent corrosion resistance,low melting point,and thereby showing recycling availability when compared to other metals.Variety experiments were conducted to select the most suitable material for marine environments.All electrochemical experiments were conducted in natural seawater.The corrosion test was performed in many methods such as anodic/cathodic polarization and Tafel analysis using multi-channel potentio/galvanostat WMPG 1000.As results,anodic and cathodic polarization behaviors indicate the characteristics of passive state and concentration polarization by reduction reaction in dissolved oxygen,which shows excellent electrochemical behaviors.Tafel analysis results show no significant difference but 5052-O alloy of various alloy materials indicates the lowest corrosion current density.Therefore,5052-O Al alloy presents most anti-corrosion material in marine environment.

Effects of Cr and Cr/Mn Combined Additions on Semi-Solid Microstructures of Al-Mg-Si Alloys Produced by D-SSF Process

The effects of Cr and Cr/Mn combined additions on the semi-solid microstructure of wrought Al-Mg-Si alloys are investigated.In the Cr-added alloy,the Al-7Cr compound is formed with homogeneously distributed in theα-Al matrix after homogenization.Both of the Al-7Cr andα-Al-（12）Mn3-Si-2 dispersiod particles are found in the homogenized microstructure of the Cr/Mn-added alloy.In the semi-solid microstructures,the smallestα-Al grains are obtained in the 60% cold-rolled alloys.After prolonged holding time,theα-Al grain size of the Cr/Mn-added alloy is smaller than that of the Cr-added alloy.Heavy deformation by cold-rolling accelerates spheroidization of theα-Al grains.The D-SSF process is found to be useful to modify the microstructures of both the Cr-added and Cr/Mn-added Al-Mg-Si alloys.

Mechanism and Inhibition of Grain Coarsening of Al-Mg-Si Alloy in Hot Forming

A high-Ti 6061 alloy was rolled with strains up to 0. 8 - 2. 0 and at 350 - 550 ℃ . Microstructures that developed during deformation and subsequent solution heat treatment (SHT) were observed by using optical and transmission electron microscopy. Microstructure evolution during SHT depends mainly on the initial rolling temperature,and it was found that the higher this temperature is,the coarser the grains are. After rolling at 400 ℃ ,well-defined cells and subgrains were formed, which induced further sites for recrystallization nucleation during subsequent SHT. The recrystallization mechanism was found to be subgrain rotation,with a final grain size smaller than 200 μm. Increasing the rolling temperature to 500 ℃ results in a low density of dislocations distributed uniformly in the deformed matrix and fewer nucleation sites during subsequent SHT. The recrystallization mechanism is grain boundary bulging,while the final grain size approaches several millimeters. Finally,a hot forming process of high-Ti 6061 alloy for inhibiting grain coarsening was proposed,and verified by experiments.

MICROSTRUCTURE AND COMPOSITION OF THE ELECTROLYTIC ETCHED PATTERN GRAINING SURFACE OF Al-Mg-Si ALLOY

After electrolytically etched pattern graining surface of aluminum alloy, it is shows that there are porous oxide film containing α Al 2O 3 and α Al 2O 3 by means of SEM XRD and XPS analysis. In the ditches, anodic oxidation makes pore density and diameter larger than other areas, and causes more coloring metal depositing and mutual cross linking. The electrolytically etched pattern surface shows relative deeper color on the ditches and lighter color on other areas, so it can be used for decoration. Electrolytic coloring metal exists in forms of Ag colloid and Ag 2O. Both anodic oxidation and electrolytic coloring affect the surface microstructure of aluminum alloy.

Microstructural heterogeneity and bonding strength of planar interface formed in additive manufacturing of Al-Mg-Si alloy based on friction and extrusion

Single-pass deposits of 6061 aluminum alloy with a single-layer thickness of 4 mm were fabricated by force-controlled friction-and extrusion-based additive manufacturing.The formation characteristics of the interface,which were achieved by using a featureless shoulder,were investigated and elucidated.The microstructure and bonding strength of the final build both with and without heat treatment were explored.A pronounced microstructural heterogeneity was observed throughout the thickness of the final build.Grains at the interface with Cu,{213}<111>,and Goss orientations prevailed,which were refined to approximately 4.0μm.Nearly all of the hardening precipitates were dissolved,resulting in the bonding interface displaying the lowest hardness.The fresh layer,subjected to thermal processes and plastic deformation only once,was dominated by a strong recrystallization texture with a Cube orientation.The previous layer,subjected twice to thermal processes and plastic deformation,was governed by P-and Goss-related components.The ultimate tensile strength along the build direction in asdeposited and heat-treated states could reach 57.0%and 82.9%of the extruded 6061-T651 aluminum alloy.

INFLUENCE OF COMPOSITION AND DISPERSOID ON FATIGUE FRACTURE BEHAVIOUR OF Al-Mg-Si ALLOYS

A study was made of the fatigue fracture behaviour under different aging conditions of two Al-Mg-Si alloys with different chemical compositions and dispersoid contents.The dispersoid phase can alter the mode of the deformation uniformity of alloys.The dispersoid it- self may decohere from the dispersoid/matrix interface under cyclic stress to form small dimples.