AZ31 Sheet Research Articles

Influence of high frequency vibration on deep drawing process of AZ31 sheet at room temperature

Quasi-ultrasonic vibration with a frequency of 15 kHz and a maximum output of 2 kW was imposed on the deep drawing process of AZ31 magnesium alloy sheet at room temperature, in order to reveal the effect of high frequency vibration on deformation behavior of AZ31 during the process. From the drawn results and the observation of the microstructure within the large deformation area, high frequency vibration has a great influence on the formability, the forming load and the failure mode of AZ31 sheet during the deep drawing process; the influence is a comprehensive result of so-called “volume effect” and “surface effect”, and relies on the vibrating amplitude. Total forming load decreased significantly as soon as the vibration superimposed. According to the tensile test results of AZ31 bars under ultrasonic vibration, the formability of AZ31 sheet increases firstly with the increase of stimulating energy, then decreases and finally becomes brittle. Under the combined influence of “surface effect” and the “softening” in the “volume effect” near the relative low amplitude of 25%A in the experiment (A is the maximum amplitude), the formability of AZ31 reaches the largest value, and the samples possess the same distribution trend of cracks as those added with lubricating oil. With the increase of excitation energy, the “volume effect” gradually becomes apparent, and finally the “hardening” of the “volume effect” occupies a dominant position.

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.

The Effect of Texture on the Corrosion Behavior of AZ31 Mg Alloy

Magnesium (Mg) grains show anisotropic corrosion behavior, which implies that the single-phase, hot-rolled Mg alloy AZ31 sheet, if highly textured, will have different corrosion performance depending on its crystallographic orientation of the grains. Its rolling surface, dominated by (0001) basal crystallographic planes, is more corrosion resistant than its cross-section surface, which is mainly composed of \( \{ 10\overline{1} 0\} \) and \( \{ 11\overline{2} 0\} \) prismatic crystallographic planes. Furthermore, grain refinement by hot rolling is beneficial to the overall corrosion resistance of AZ31 because of the dissolution of AlMn(Fe) intermetallic precipitates in the alloy. Surface compressive deformation machining can lead to refined grains and an expected preferred grain orientation, thus improving the corrosion resistance of AZ31 alloy.

Effect of the welding parameters and tool configuration on micro- and macro-mechanical properties of similar and dissimilar FSWed joints in AA5754 and AZ31 thin sheets

The effect of welding parameters and tool configuration on the surface appearance, mechanical and microstructural properties of similar and dissimilar FSWed joints in AA5754 and AZ31 thin sheets was widely investigated. Two different tool configurations, with and without the pin, were used. As far as the similar friction stir welded joints in AZ31 and in AA5754 alloys are concerned, it was shown that the “pinless” tool leads to the obtaining of higher values of the tensile strength and ductility as compared to the “pin” one. On the contrary, by considering the dissimilar friction stir welding between AZ31 and AA5754 thin sheets, the welding process becomes very critical as the “pinless” tool is used. Sound dissimilar joints were obtained using the “pin” tool configuration, even though the effect of the material position with respect to the welding tool is a very important factor to be considered. A marked improvement in the surface appearance and mechanical properties was obtained by placing aluminium alloy in the advancing side and magnesium alloy in the retreating one. An investigation has been also carried out in order to evaluate the microstructural properties of similar and dissimilar welded joints.

Material modeling of AZ31 Mg sheet considering variation of r-values and asymmetry of the yield locus

A commercial AZ31 magnesium alloy sheet was tested under uniaxial tension/compression loading and proportional biaxial tensile loading using cruciform specimens. Plastic work contours and directions of the plastic strain rates were determined over a range of equivalent plastic strain, 0.001 ≤ ε 0 p ≤ 0.008 , to quantitatively determine the elastic–plastic deformation behavior. The shape of the work contours changed with plastic strain and the r -values increased with plastic strain. The measured work contours and directions of plastic strain rates were compared with those predicted using selected yield functions in the first quadrant of the stress space. A recently proposed yield function, CPB2006 [O. Cazacu, B. Plunkett, F. Barlat, Int. J. Plast. 22 (2006) 1171–1194] was also evaluated to account for the asymmetry of the yield locus with consideration of the uniaxial compression test data. The standard deviation between the measured and calculated data for the work contours and the directions of plastic strain rates were calculated, allowing the validity of these yield functions to be evaluated. The CPB2006 yield criterion with an exponent of 3 provided a fairly accurate description of the anisotropy and asymmetry of the work contours for the AZ31 sheet.

The effect of initial grain size and temperature on the tensile properties of magnesium alloy AZ31 sheet

Abstract This research aimed to assemble and review data that are relevant to sheet metal formability of the magnesium alloy AZ31. Rolled sheets were processed to give four different grain sizes in the range from 2.9 to 47.1 μm. Similar basal textures were present in all these conditions. Tensile tests were carried out at various temperatures between 25 °C and 240 °C, with some additional tests also made below room temperature in dry ice. Results are presented and discussed relating to strength, ductility, strain rate sensitivity and anisotropy. An optimum grain size of about 7 μm applies for ductility over most of the temperature interval. Uniform elongation decreases steadily with increasing temperature whereas the post-necking and total elongation values increase markedly. Measurements of strength, anisotropy and strain rate sensitivity all indicate a significant role of grain boundary mediated deformation above room temperature. The plastic strain ratio, r, is high at room temperature but decreases considerably, especially for the fine grained conditions, at higher temperatures. Modifications to the active slip modes also occur over the same temperature interval but their effect on plasticity is probably less important than was previously believed.

Effects of phosphate pretreatment and hot-humid environmental exposure on static strength of adhesive-bonded magnesium AZ31 sheets

An innovative phosphate–permanganate surface treatment (PPT) was developed to improve the static strength of adhesive-bonded 4mm thick magnesium AZ31 sheets. The phosphate coating having the chemical composition of 1.43% P, 1.63% F and 0.15% Mn (in mass %) was formed after the treatment with PPT solution which has the formulation of KMnO4, K2HPO4, Na2SiO3 and NaF. The combination of additives NaF and Na2SiO3 and the pH values in the range of 5–6 for a phosphate–permanganate solution was found to be the key elements for the formation of the phosphate coating. The appearance of the phosphate coating and corrosion resistance to 3.5%NaCl solution was assessed. To study the durability of the coating, the effect of an exposure in a hot-humid environment (96% R.H. at 40°C) on the static strength of adhesive-bonded magnesium AZ31 was investigated. Test results showed that the phosphate coating improved not only the static strength of bonded magnesium AZ31 joints in an ambient condition but also the durability in a hot-humid environment. These results suggest that PPT surface pretreatment is capable of improving the static strength and thermal durability of adhesive-bonded magnesium AZ31 sheets.

Dynamic recrystallization of the H- and O-tempered Mg AZ31 sheets at elevated temperatures

Abstract Uniaxial tensile properties influenced by the dynamic recrystallization (DRX) behavior of the partially strain-hardened magnesium AZ31 sheets (H24) containing scores of twins were investigated and compared to those of fully annealed ones (O) with absence of twins. For this purpose, a series of uniaxial tensile tests were carried out for the H24 and O materials at temperatures ranged from room temperature to 300 °C and at strain rates between 10−3 and 10−1 s−1. At 150 and 200 °C, the H24 material exhibited higher yield strength without much loss in elongation compared to those of the O material; this trend was attributed to the continuous DRX along or around grain boundaries as well as extensive twin-aided DRX inside grains. In addition, the post-deformation hardness value of the H24 material showed higher than that of the O material. On the other hand, at higher temperatures of 250 and 300 °C, it was observed that twins shown in the H24 material were disappeared even prior to deformation, resulting in the similar grain structure and mechanical property values to those of the O material, e.g., discontinuous DRX associated with grain boundary bulging. Finally, the initiation of DRX was rationalized in terms of microstructure morphology, deformation temperature and strain rate, and then modeled in the context of strain hardening rate analysis. A comparison of experimental results and predictions for both H24 and O materials showed that the model can provide a reasonable prediction of critical strain to initiate DRX.

Investigation to Self-Piercing Riveting of Wrought Magnesium AZ31 Sheets

In this study, the fabrication of the desired SPR joints was investigated as a function of the preheat temperature and strain rate. To determine the optimum preheat temperature, Gleeble thermal analogue testing of 2mm thick magnesium AZ31 was used to assess the combined influence of preheat temperature and strain rate on the strength and total elongation of magnesium AZ31. Magnesium alloy AZ31 with a thickness of 2mm was preheated with various temperatures prior to self-piercing riveting. The appearances, cross-sections and mechanical tests of the SPR magnesium AZ31 joints were investigated. It was found that a preheat temperature of 180 to 200oC largely eliminated the cracking in magnesium AZ31 joints. The joint strength increases with increasing preheat temperature from ambient to 200oC. The strength increase is attributed to the reduction in joint cracking and an increase in mechanical interlock between the rivet and work pieces.

Evaluation of Seven Ductile Fracture Criteria for Failure Prediction of AZ31 Sheet in Warm Forming

Seven commonly used ductile fracture criteria are briefly reviewed and the validity of predicting the failure of AZ31 Mg alloy sheet by using these ductile fracture criteria is evaluated. Through fitting the experimental FLCs, the damage parameters for these ductile fracture criteria are determined firstly. Integrating these seven ductile fracture criteria into Abaqus/Explicit via VUMAT subroutine, the warm deep drawing process of AZ31 Mg alloy sheet is simulated. The limit drawing ratios (LDR) of AZ31 Mg alloy sheet at different temperature are predicted. The comparison of predictions with the experimental results has shown that the combination of the finite element simulation and the ductile fracture criterion is useful for predicting the fracture occurred in warm deepdrawing of AZ31 Mg alloy sheet.

Evolution of Texture and Microstructure of AZ31 Mg Alloy Sheet at High Strain Rates

The high strain rate behaviour of magnesium alloys is of great interest to automotive,aerospace and/or defence industries because some critical components should have the propermechanical properties to work under crash or impact conditions. In the current study, resultsfrom an extensive experimental program are presented. The uniaxial mechanical behaviour ofAZ31 sheet under dynamic conditions (ε=103 s-1) is analyzed and compared with that observedat low strain rates. AZ31 sheets have been tested in tension and compression using Hopkinsonbar apparatus at 25°C and 250°C. Moreover, interrupted tests were also performed in orderto relate the evolution of deformation mechanisms with strain. Finally, detailed microstructureand texture examination by electron backscatter di raction (EBSD) and neutron di ractionhas been carried out in order to elucidate the predominant deformation and recrystallizationmechanisms.

AZ31 합금의 부풀림 성형시 공공의 거동

Based on the facts that AZ31 magnesium alloy can be blow formed just like superplastic aluminum alloys and that most superplastic alloys fail by cavitation, the present study was undertaken to investigate the cavitation behavior of a fine-grained AZ31 sheet during blow forming at the elevated temperature. Other points of interest included the much lower strain rate and temperature dependencies of the magnesium alloy compared with conventional superplastic alloys. It was also aimed to find if cavitation in the AZ31 alloy can be suppressed by hydrostatic pressure, as is the case in most superplastic alloys. Interestingly, the application of hydrostatic pressure did not increase the blow formability of AZ31 sheet, even though it reduced the degree of cavitation. A possible reason for this behavior is discussed.

인장-압축 비대칭성을 고려한 AZ31 판재의 항복함수 구성

In order to take into account the strong anisotropy and the tension-compression asymmetry of AZ31 sheet alloy, the Cazacu-Plunkett-Barlat yield criterion(Cazacu, 2006), CPB06, was adopted in the present material modeling. The variation of anisotropic coefficients which describe the yield surface evolution of AZ31 is optimized using an interpolation function based on specific calibration results. It generates continuous yield surfaces, which makes it possible to describe the different hardening rates in tension and compression as well as tension-compression asymmetry of magnesium alloys. The ability of the CPB06 yield criterion to predict experimental results was demonstrated and compared with that of the Hill(1948) yield criterion.

Metallurgical analysis of magnetic pulse welds of AZ31 magnesiumalloy

Magnesium AZ31 sheets have been lap welded with magnetic pulse weldingusing H shaped symmetric coils connected to a Pulsar MPW-25 capacitor bank.The joints displayed an increasing trend in strength with discharge energy.The weld morphology consisted of twin bond zones separated by an unbondedcentre zone. Metallographic examination of the unbonded centre zone revealedanisotropic deformation and a lack cleaning from the interface. This zoneforms as a result of normal impact in the initial stage of collision. Transmissionelectron microscopy of the bond zone revealed a continuous interface havingan 8–25 μm thick interlayer with dislocation cell structure anddistinct boundaries with adjacent material. The interlayer may have formedin a semisolid state at elevated temperature. The interlayer corresponds toa ductile fracture surface and is responsible for the joint’s high strength.Nanoscale grains were found beside the interlayer as well as larger, highlyelongated grains.

Twinning and grain subdivision during dynamic deformation of a Mg AZ31 sheet alloy at room temperature

The microstructural evolution of an AZ31 rolled sheet during dynamic deformation at strain rates of ∼10 3 s −1 has been investigated by electron backscatter diffraction, X-ray and neutron diffraction. The influence of orientation on the predominant deformation mechanisms and on the recovery processes taking place during deformation has been systematically examined. The results have been compared with those corresponding to the same alloy tested quasi-statically under equivalent conditions. It has been found that strain rate enhances the activation of { 1 0 1 ¯ 2 } extension twinning dramatically, while contraction and secondary twinning are not significantly influenced. The polarity of { 1 0 1 ¯ 2 } extension twinning is even reversed in some grains under selected testing conditions. Significant grain subdivision by the formation of geometrically necessary boundaries (GNBs) takes place during both quasi-static and dynamic deformation of this AZ31 alloy. It is remarkable that GNBs of high misorientations form even at the highest strain rates. The phenomenon of recovery has been found to be orientation dependent.

Microstructure and mechanical properties of magnesium AZ31 sheets produced by extrusion

In the last decade magnesium has regained importance for lightweight and transportation industries since it is the lightest metal for structural applications. Therefore the increasing demand of sheet-like magnesium applications required manifold forming strategies. The extrusion is an alternative solution for the production of magnesium sheets and thin flat profiles, which are produced today mainly by rolling. This study presents the influence of the process temperature and extrusion ratio on the microstructure and mechanical properties of AZ31 extrusion sheets. The extruded sheets exhibit a coarse-grained microstructure and a pronounced mechanical anisotropy in the sheet plane caused by the extrusion texture. This texture leads to a strong dependence of deformation systems on the loading direction delivering the highest value for yielding in extrusion direction, but the lowest in transverse direction due to the easy activation of the {10-12} extension twinning system in favorably oriented grains.

Effect of impurity reduction on rollability of AZ31 magnesium alloy

The effect of impurity reduction on the hot rolling behavior of AZ31 magnesium alloy was systematically investigated in this study. In the as-cast alloys, the total content of main impurity elements such as Fe, Si, Cu, and Ni was varied from 0.0462 to 0.0163 wt% by changing the purity of used raw magnesium metals. The alloys after homogenization were subjected to hot rolling at 300 °C with a reduction of 20% per pass. It was found that the initiation of edge cracks is postponed with reducing impurity level in the alloys. And the maximum rolling reduction prior to edge cracking increases from 34 to 58% as the impurity content drops from 0.0462 to 0.0163 wt%. Microstructural observations showed that smaller grains are present in the alloy with lower impurity content in the cast and homogenization states. Moreover, decreasing impurity content leads to a reduced number of deformation twins and an enhanced volume fraction of small recrystallized grains in the as-rolled microstructure, which indicates that impurity reduction is beneficial to the recrystallization process and subsequent plastic deformation. Based on the results, the enhancement in hot rollability of the AZ31 sheet by impurity reduction should be due to finer grain size, the reduced number of deformation twins and the enhanced extent of recrystallization.

Improving the sheared edge in the blanking of commercial AZ31 sheet through texture modification

Commercial rolled magnesium sheets of alloys AZ31 (Mg–3 mass%Al–1 mass%Zn) and ZE10 (Mg–1 mass% Zn–<1 mass% Rare Earths) in O-temper condition were used for blanking experiments near room temperature. A serrated fracture surface can be observed in case of AZ31 but not in case of ZE10. During the shearing process of the AZ31 sheet, many micro cracks parallel to the sheet plane are generated in the shearing zone. These micro cracks lead to the formation of loose particles during the shearing operation, which interfere with further processing of the part and incur additional costs by increasing the scrap rate. It is found that the strong basal texture of this alloy is an important reason for the generation of such serrated cracks. In this paper a new method of selective texture modification is described to locally change the mechanical properties of the AZ31 sheet. Subsequent shearing experiments show a significant change in the material behavior, especially regarding the direction of crack propagation, which leads to a better shearing performance. The commonly observed serrated crack does not occur any more after this local treatment and the sheared edge is clearly improved.

Die Parameters Optimized for Drawing of AZ31 Magnesium Alloy Sheet by Finite Element Method

In this study AZ31 sheet with a thickness of 1.2mm and diameter of 52mm was simulated to press into a dish by a finite element method(FEM) software, which to obtain better processing of plastics forming of magnesium alloy by varying die parameters. In order to find the way of development on drawing property and to formulate the rational stamping processing, simulations have been applied on the maximum principal stress various with round radius of dent die and round radius of punch and die gap. Simulation results show that: to obtain a dish of 29mm diameter, a sheet of AZ31 magnesium with a thickness of 1.2mm and diameter of 52mm has been drawn, the fracture occurring at the corner of dish wall bottom. the ability of drawing varies with the round radius of dent die, which better radius is 3.8 mm. In the same way better round radius of punch is 3.0 mm, while better half gap is 1.8mm. Experiments also show that high diameter ratio has been increased with the various of die parameters and forming ability of material has been developed. It is reliable of simulation of finite element method.

Grain Refinement of Magnesium Alloy AZ31 by Repeated Cold Rolling and Annealing

This work focused on the grain refinement and investigation its effect on the microstructural evolution and mechanical properties. The magnesium alloy AZ31 sheet was processed by repeated cold rolling and recrystallized annealing. From the experimental works, the fine and equiaxed grains with less than 5 μm were achieved. It was found that for annealing at temperatures in the range of 523–673K, sample was fully recrystallized less than 30 minutes and after that the growth of the recrystallized grains is slight. Finally, the tensile tests were carried out to analyze the changes in the strength and fracture elongation.