Mechanical Evaluation of AZ80 Magnesium Alloy in Cast Wrought Form

Wrought magnesium alloy AZ80 with a thick section of 20 mm was prepared by squeeze casting (SC) and permanent steel mold casting (PSMC). The porosity measurements of the SC and PSMC depicted that SC AZ80 had a pore content of 0.52%, which was 77% lower than 2.21% of PSMC AZ80 counterpart. The YS, UTS, ef, E and strengthening rate of cast AZ80 were determined by mechanical pulling. The engineering stress versus strain bended lines showed that SC AZ80 had a YS of 84.7 MPa, a UTS of 168.2 MPa, 5.1% in ef, and 25.1 GPa in modulus. But, the YS, UTS and ef of the PSMC AZ80 specimen were only 71.6 MPa, 109.0 MPa, 1.9% and 21.9 GPa. The findings of the mechanical pulling evidently depicted that the YS, UTS, ef and E of SC AZ80 were 18%, 54%, 174% and 15% higher than PSMC counterpart. The computed resilience and toughness suggested that the SC AZ80 exhibited greater resistance to tensile loads during elastic deformation and possessed higher capacity to absorb energy during plastic deformation compared to the PSMC AZ80. At the beginning of permanent change, the strengthening rate of SC AZ80 was 10,341 MPa, which was 9% greater than 9489 MPa of PSMC AZ80. The high mechanical characteristics of SC AZ80 should be primarily attributed to its low porosity level. .

Effects of Ce addition on microstructure, mechanical properties and corrosion resistance of as-cast AZ80 magnesium alloy

In this study, Ce was introduced into the AZ80 alloy and the effects of Ce addition on the microstructure, mechanical properties and corrosion resistance of the as-cast AZ80 magnesium alloy were investigated. The results show that the addition of Ce into the AZ80 alloy can not only refine the microstructure, but also result in the formation of the needle-like Al4Ce phase. These tiny Al4Ce phases are homogeneously distributed at grain boundaries and within grains. An appropriate Ce addition can also change the β-Mg17Al12 phase at the grain boundaries from continuous network to small island-like. At the same time, with the increase of Ce content from 0 to 2.0wt.%, the macro-hardness of the as-cast alloy is enhanced linearly, while impact toughness, tensile strength and elongation all firstly increase and then decrease. The AZ80 alloy containing 1.0wt.% Ce exhibits the optimal properties. Its macro-hardness, impact toughness, tensile strength and elongation are 61.90 HB, 15.50 J·cm-2, 171.80 MPa and 3.35%, increase by 9.95%, 63%, 13.3% and 36.7%, respectively compared with the base alloy. In addition, Ce can enhance the corrosion resistance of the AZ80 magnesium alloy.

Modeling of microstructure evolution of AZ80 magnesium alloy during hot working process using a unified internal state variable method

In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the interactive effects of material hardening, recovery and dynamic recrystallization(DRX) on the characteristic deformation behavior were considered by incorporating the evolution laws of viscoplastic flow, dislocation activities, DRX nucleation and boundary migration in a coupled manner. The model parameters were calibrated based on the experimental data analysis and genetic algorithm(GA) based objective optimization. The predicted flow stress, DRX fraction and average grain size match well with experimental results. The proposed model was embedded in the finite element(FE) software DEFORM-3 D via user defined subroutine to simulate the hot compression and equal channel angular extrusion(ECAE) processes. The heterogeneous microstructure distributions at different deformation zones and the dislocation density evolution with competitive deformation mechanisms were captured.This study can provide a theoretical solution for the hot working problems of magnesium alloy.

High-temperature mechanical properties of as-extruded AZ80 magnesium alloy at different strain rates

The mechanical properties of as-extruded AZ80 magnesium alloy at temperatures of 450-525℃ and strain rates of 3.0 s^(−1)and 0.15 s^(−1)were investigated by tensile tests.Zero ductility of alloy appeared at 500℃ with a strain rate of 0.15 s^(−1),while the zero strength and zero ductility of the alloy were obtained nearly simultaneously at 525℃ with a strain rate of 3.0 s^(−1).The results indicated that the lower strain rate accelerated the arrival of zero ductility.As the temperature increased,the failure mode of the alloy developed from trans-granular fracture to cleavage fracture and then to inter-granular fracture with the feature of sugar-like grains and fusion traces.The existence of the low-melting composite ofβ-Mg_(17)Al_(12) and Al_(8)Mn_(5) particles segregated near the Mg_(17)Al_(12) phase along grain boundaries were demonstrated to be the reason for the brittle fracturing of the AZ80 alloy at high temperatures.Furthermore,microstructural evolution at temperatures approaching the solidus temperature was discussed to clarify magnesium alloy’s high temperature deformation mechanism.

Effects of temperature and strain rate on critical damage value of AZ80 magnesium alloy

A series of AZ80 billets were compressed with 60%height reduction on hot process simulator at 250,300,350,400℃ under strain rates of 0.01,0.1,1 and 10 s- 1.In order to predict the occurrence of surface fracture,the values of the Cockcroft-Latham equation were calculated by the corresponding finite element numerical algorithm developed.A concept about damage incremental ratio in plastic deformation was defined as the ratio of damage increment at one step to the accumulated value.A method of finding the intersection of incremental ratio varying curve and simulation step axis was brought forward to make the fracture step certain. Then,the effects of temperature and strain rate on critical damage value were achieved.The results show that the critical damage value is not a constant but changes in a range of 0.021 8-0.378 0.It decreases significantly with the increase of strain rate at a certain temperature.While under a certain strain rate,the critical damage value has little change with the increase of temperature.

Fracture behaviors of AZ80 magnesium alloy during multiple forging processes

The initiation, propagation and the accompanied dislocation structures of the cracks in AZ80 magnesium alloy during multiple forging processes were investigated. The results show that the cracks firstly initiate at the Mg/Mg17Al12 interface under the hoop tensile stress on equatorial free surface. On further deformation, the cracks in the Mg17Al12 particles tend to propagate along the grain boundaries(GBs) in a zigzag pattern and link with adjacent cracks in other Mg17Al12 particles to form one whole crack, leading to the fracture surface. Low deformation temperature and too many forging passes during the deformation will promote the nucleation of interfacial microcrack inside the specimens due to the strong plastic strain incompatibility and the high internal stresses near the GBs. The loading axis rotating during the process can change the stress field at the tip of cracks, leading to the change of the crack propagating path and assisting in inhabiting microcracking development.

Preparation and thixoforging of semisolid billet of AZ80 magnesium alloy

Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation.Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA.Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape.The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.

Corrosion properties of plastically deformed AZ80 magnesium alloy

AZ80 magnesium alloys were deformed at 200,250,300,350 and 400℃ with different deformation degree of 50%,75%, 83%,87%and 90%,respectively.The corrosion properties of different deformed AZ80 samples were studied by galvanic test in 3.5%NaCl solution.The results show that plastic deformation could improve the corrosion resistance of AZ80 alloy;and the corrosion rate of AZ80 deformed at 250℃ with the deformation degree of 83%was the lowest,which was 33%of the as-cast AZ80 alloy.Further studies of the microstructure show that the refined grain size and continuously distribution ofβphase around the grain boundary did have a positive effect on the improvement of corrosion resistance of AZ80 alloys.For AZ80 alloys,the smaller the grain size is,the more homogeneous the structure is,and the better the corrosion resistance is.

Effect of thermal processing on microstructure and mechanical properties of AZ80 magnesium alloy

The influences of deformation temperature and deformation degree on the microstructure and mechanical properties of AZ80 magnesium alloy were investigated by the adoption of isothermal plain strain compression experiment.The results show that thermal compression processing can refine the grain size and the tensile strength of all the deformed AZ80 magnesium alloys is increased to the maximum of 320 MPa.With the increasing of deformation temperature,the tensile strength decreases;with the increasing of the deformation degree,the tensile strength increases significantly in the temperature range of 200-300℃and becomes stable at temperature higher than 300℃.During the compression processing of AZ80 magnesium alloys,at lower temperature (<300℃),dynamic recrystallization is incomplete and a certain hardening effect is preserved,which makes great effect of deformation degree on the properties.At higher temperature(>300℃),dynamic recrystallization is complete and refined grain strengthening is dominant,leading to little effect of deformation degree on mechanical properties.

Precipitation behavior and effect of new precipitatedβphase in AZ80 magnesium alloy

Granular precipitate that was a new kind ofβ-Mg17Al12 phase found in aged AZ80 wrought Mg alloy at all aging temperature was studied. The structure and precipitation behavior of this granularβ-Mg17Al12 precipitate were studied by environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM). The effect of the granular precipitate on mechanical properties of AZ80 alloy was also studied. The new precipitate that was granular and nucleated both on grain boundaries (GBs) and twin boundaries, has the same crystal structure and lattice parameter as those of the continuous or discontinuous precipitatedβ-Mg17Al12. And the nucleation and growth of the granular precipitate are faster than those of the other two precipitates at higher temperatures (above 583 K), but are suppressed at lower temperatures (below 423 K). At lower temperatures, the discontinuousβ-Mg17Al12 precipitates firstly and the granularβ-Mg17Al12 precipitates after aged more than 40 h. The crack is easily nucleated on the phase boundaries of granular phase and matrix because of the weak binding force. As a result, the strength and ductility of AZ80 Mg alloy are decreased by the granularyβ-Mg17Al12 precipitate.

液态模锻浇注温度对AZ80机械壳体力学性能和抗氧化性能的影响

为了探索浇注温度对液态模锻AZ80机械壳体力学性能和抗氧化性能的影响规律,在熔炼温度720℃、比压力50 MPa、压头速度60 mm/s、充型速度8 m/s、充型时间1.1 s、保压时间10 s和模具预热温度280℃不变的情况下,采用不同的浇注温度进行AZ80镁合金机械壳体试样液态模锻试验,并进行了试样室温力学性能以及350℃×24 h抗氧化性能的测试与分析。结果表明:在浇注温度从610℃增加搭到670℃,试样力学性能和抗氧化性能先提高后下降。AZ80镁合金机械壳体试样液态模锻的浇注温度优选为655℃。

The effects of deformation parameters and cooling rates on the aging behavior of AZ80+0.4%Ce

The extruded AZ80+0.4%Ce magnesium alloy was twisted in the temperature range of 300-380℃by using a Gleeble 3500 thermal simulation test machine with a torsion unit.The deformed cylindrical specimens were cooled at a cooling rate of 10℃/s or 0.1℃/s,respectively,and aged at 170℃.The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center(SRPC),and that the strong initial basal texture of the extruded magnesium alloy was weakened.Both continuous and discontinuous dynamic recrystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated.And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300℃.For the specimens deformed at 300℃and 340℃followed by a slow cooling rate(0.1℃/s),precipitates of various shapes(β-Mg_(17)Al_(12)),with the dominant precipitates being on the grains boundaries,appeared on the surface section.For specimen deformed at 380℃,lamellar precipitates(LPS)in the interiors of the grains were predominant.After aging,the LPS still dominated for specimens twisted at 380℃;however,the LPS gradually decreased with decreasing deformation temperatures from 380℃to 300℃.Dynamically precipitatedβ,especially those decorating the grain boundaries,changed the competition pictures for the LPS and precipitates of other shapes after aging.Interestingly,LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures.Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain,reduced precipitates size,decreased lamellar spacing as well as strain hardening.

Dynamic and Static Aging Precipitation of β-Mg_(17)Al_(12) in the AZ80 Magnesium Alloy During Multi-directional Forging and Subsequent Aging

Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.

Effect of heat treatment on the microstructure and mechanical properties of AZ80M magnesium alloy fabricated by wire arc additive manufacturing

To maximize the benefits of wire arc additive manufacturing(WAAM)processes,the effect of post-deposition heat treatment on the microstructure and mechanical properties of WAAM AZ80M magnesium(Mg)alloy was investigated.Three different heat treatment procedures(T4,T5 and T6)were performed.According to the results,after T4 heat treatment,the microsegregation of alloying elements was improved with the eutectic structure dissolved.Samples after T5 heat treatment inherited the net-like distribution of secondary phases similar to the as-deposited sample,where the eutectic structure covering the interdendritic regions and theβ-phase precipitated around the eutectic structure.After T6 heat treatment,the tinyβ-phases re-precipitated from the matrix and distributed in inner and outer of the grains.The hardness distribution of the samples went through T4 and T6 heat treatment was more uniform in comparison to that of T5 heat treated samples.The tensile test showed that the T6 heat treatment improved the strength and ductility,and the anisotropy between horizontal and vertical can be eliminated.Moreover,T4 treated samples exhibited highest ductility.

Corrosion of Artificial Aged Magnesium Alloy AZ80 in 3.5 wt pct NaCl Solutions

The corrosion morphologies of aged magnesium alloy AZ80 were investigated by immersion corrosion tests, scanning electron microscopy （SEM）, electrochemical measurement. The T5 heat treatment was carried out in a vacuum furnace, holding for 16 h at 177℃, and then cooling in air. The results showed intergranular corrosion （IGC） occurred as an aged AZ80 sample was immersed in 3.5 wt pct NaCI aqueous solution for 1 h and the narrow path attack progressed predominantly along the bulk β phase in the grain boundaries or took place in the eutectic areas. IGC was attributed to the network distribution of β phase along the grain boundaries, the depleted aluminium in the precipitation areas and the breakdown potential.

Effect of strain,strain rate and temperature on workability of AZ80 wrought magnesium alloy

The hot deformation behavior of AZ80 wrought magnesium alloy was studied in the temperature range of 523-673 K and the strain rate range of 0.01-10 s-1 using hot compression tests.Through the flow stresses behavior,the processing maps were calculated and analyzed according to the dynamic materials model.The stable,metastable and unstable regimes were clarified.The optimum processing conditions were suggested as following:the DRX regions in Domain #1-0.25,Domain #2-0.25,Domain #1-0.45,Domain #2-0.45,Domain #3-0.45,Domain #1-0.65 and Domain #1-0.85,and the DRV regions in Domain #3-0.25 and Domain #4-0.45.In each "safe" DRX domain,it is preferable to conduct hot working in the small region around efficiency peak point.The strain has a great influence on the processing maps.The whole area of the "safe" domains increases with the increase of true strain from 0.25 to 0.65,while it decreases with the increase of true strain from 0.65 to 0.85.The results of kinetic analysis reveal that the values of apparent activation energy in all the domains are higher than that for self-diffusion in pure magnesium (135kJ/mol),and the deformation mechanism in all the domains is likely to be cross-slip.

电解液成分对AZ80镁合金微弧氧化膜耐蚀性的影响

为提高AZ80镁合金的耐蚀性,采用微弧氧化技术在镁合金表面原位生长氧化膜,主要研究电解液成分Na_(2)SiO_(3)和NaOH浓度对微弧氧化膜耐蚀性的影响。借助X射线衍射仪和能谱仪分析氧化膜的化学组成;借助扫描电镜分析氧化膜的微观形貌;采用中性盐雾试验表征氧化膜的耐蚀性。结果表明:镁合金氧化膜耐蚀性随Na_(2)SiO_(3)浓度的增加,先提高后下降,随着NaOH浓度的增加而提高。最优电解液配比下制备的氧化膜经96 h中性盐雾试验未发生腐蚀,这种优异的耐蚀性归因于表面生成的Mg_(2)SiO_(4)陶瓷相和自封孔结构。

孪晶界第二相析出对AZ80镁合金板材弯曲变形行为的影响

采用光学显微镜(OM)、扫描电镜(SEM)研究了室温预置拉伸孪晶后时效处理对AZ80镁合金第二相的析出和弯曲变形行为的影响。结果表明,在180℃时效0.5 h可明显促进第二相粒子在晶界处的析出,增加孪晶界亦可促进第二相的析出。预置孪晶后进行反向拉伸,AZ80镁合金组织发生去孪生行为,组织中孪晶数量减少。由于去孪生行为的产生,拉伸屈服强度降低。将预置孪晶的试样在100℃弯曲变形后,弯曲试样外侧发生拉伸去孪生行为,内侧组织因为压缩载荷的作用孪晶数量增加,中部呈孪晶数量由多变少的过渡现象。第二相粒子增多会抑制去孪生行为的产生。

Influence of texture and microstructure on mechanical properties of high-strength wrought magnesium alloy AZ80

Monotonic (tensile and compressive) and high cycle fatigue properties of the forged magnesium alloy AZ80 were investigated by using specimens with load axis parallel to longitude (L) or transverse (T) direction. A pronounced directional anisotropy in monotonic tests was observed in AZ80, i.e. the yield stress in T-direction is significantly lower than that in L direction. However, the directional anisotropy is absent in fatigue, fatigue strengths in both L- and T-directions are essentially equal. The absence of directional anisotropy in fatigue is possibly associated with the microstructure of AZ80. A homogeneous single phase structure probably alleviates the directional anisotropy of fatigue properties of the wrought magnesium alloy.

多向锻造工艺对AZ80镁合金显微组织和力学性能的影响

通过多向锻造工艺制备出了组织均匀、晶粒尺寸为1-2 μm的AZ80镁合金锻坯．经7个道次锻压,材料硬度、屈服强度和抗拉强度达到最大,分别为87．3 HB,258．78 MPa和345．04 MPa,是锻前试样硬度的1．43倍、强度的2倍;伸长率在6个道次达到最大,为7．85％,是锻前的2．45倍．多向锻造工艺下,材料内部易形成交错变形带,有利于组织细化．形变诱导晶粒细化是主要的晶粒细化机制．晶粒细化过程存在一临界应变量εc(2≤εc≤2．4),当实际应变量εx超过临界应变量εc 时,材料基本为动态再结晶细晶组织,进一步细化变得困难．铸态试样室温拉伸断口为准解理断裂加少量剪切断裂,锻后试样断口出现大量细小韧窝．随应变量的增加,韧窝数目增多,分布趋向均匀,材料延性增大,