Two-stage dynamic recrystallization and texture evolution in Al-7Mg alloy during hot torsion

Hot torsion tests were performed on the Al-7Mg alloy at the temperature ranging from 300 to 500℃ and strain rates between 0.05 and 5 s^(-1) to explore the progressive dynamic recrystallization(DRX)and texture behaviors.The DRX behavior of the alloy manifested two distinct stages:Stage 1 at strain of≤2 and Stage 2 at strains of≥2.In Stage 1,there was a slight increase in the DRXed grain fraction(X_(DRX))with predominance of discontinuous DRX(DDRX),followed by a modest change in X_(DRX) until the transition to Stage 2.Stage 2 was marked by an accelerated rate of DRX,culminating in a substantial final X_(DRX) of~0.9.Electron backscattered diffraction(EBSD)analysis on a sample in Stage 2 revealed that continuous DRX(CDRX)predominantly occurred within the(121)[001]grains,whereas the(111)[110]grains underwent a geometric DRX(GDRX)evolution without a noticeable sub-grain structure.Furthermore,a modified Avrami’s DRX kinetics model was utilized to predict the microstructural refinement in the Al-7Mg alloy during the DRX evolution.Although this kinetics model did not accurately capture the DDRX behavior in Stage 1,it effectively simulated the DRX rate in Stage 2.The texture index was employed to assess the evolution of the texture isotropy during hot-torsion test,demonstrating significant improvement(>75%)in texture randomness before the commencement of Stage 2.This initial texture evolution is attributed to the rotation of parent grains and the substructure evolution,rather than to an increase in X_(DRX).

The Solidification Behavior of Mg-9Al-2Ca Alloy under Furnace Cooling

To understand the solidification pathway and microstructure evolution of Mg-9Al-2Ca alloy,the cooling curve of the alloy solidified under furnace cooling was measured and the water-quenched samples were observed.The experimental results show that the matrix phase of α-Mg dendrites is first generated at 596℃ during the solidification process,then the eutectic phases of Al_(2)Ca and Mg_(17)Al_(12) are formed at 518 and 447℃,respectively,and the solidification is terminated at 436℃.In the process of solidification,the seaweed dendrites of α-Mg get coarser and are gradually transformed into the global dendrites;besides,the secondary dendrite arms spacing(SDAS)of α-Mg as well as the solid fraction are both increased,while the increasing rate of SDAS of α-Mg and the solid fraction in the temperature region of 600-550℃ is faster than that in the temperature region of 550-436℃.And a power function relationship can be used to illustrate the change of the SDAS and the solid fraction with the temperature of solidification.

挤压态Mg-(6～9)Al-Zn的组织性能和断裂行为分析

通过金相观察、拉伸试验和SEM分析等方法,研究了挤压态Mg-(6～9)Al-Zn合金的显微组织和力学性能。结果表明,挤压工艺使铸态下粗大枝状晶变成均匀细小等轴晶,随着Al含量增加,合金抗拉强度、硬度和晶粒大小均呈升高趋势,而伸长率先上升后下降。AZ91综合性能最优,抗拉强度、屈服强度和伸长率分别达336.7MPa、245.3MPa和17.1%。Mg-(6～9)Al-Zn合金均表现为准解理断裂特征,适当的Al含量有利于改善合金的综合性能,但Al含量过高所形成的脆性β(Mg17Al12)相加剧了镁合金的断裂倾向。

纳米SiC颗粒对Mg9Al-1Si合金组织及力学性能的影响

研究了纳米Si C颗粒对Mg9Al-1%Si(以下记作Mg9Al-1Si)合金显微组织和力学性能的影响。研究结果表明:Mg9Al-1Si合金组织由α-Mg基体、网状β-Mg17Al12相及粗大汉字状或细长鱼骨状两种形态的Mg2Si相组成。加入质量分数为1%的纳米Si C颗粒,Mg9Al-1Si合金的α-Mg基体晶粒明显细化;β-Mg17Al12相变细变小,网状分布改善不大;粗大汉字状Mg2Si相消失,鱼骨状的Mg2Si相变得更加细小。合金的力学性能得到显著提高,屈服强度提高了13.5%;抗拉强度提高了54%;伸长率由0.48%提高到1.56%,提高了225%.

Dynamic recrystallization during hot torsion of Al-4Mg alloy

Binary Al-4Mg alloy have been deformed by hot torsion at 300-500 deg C andstrain rates of 0.006-1.587 s^(-1) to a true strain of 5.5. The specimens were annealed in vacuumfor 1.5 h at 500 deg C and then water quenched. The study indicates that the dynamicrecrystallization occurs during hot torsion of Al-4Mg alloy in a certain range of Z parameter(Zener-Hollmon Parameter), i.e. 19.3 <= lnZ <=24.8. Increasing the strain rate at higher deformationtemperature or reducing the strain rate at lower deformation temperature accelerates the occurrenceof dynamic recrystallization in the alloy.

Microstructure of the Hypoeutectic Al-Mg Alloy Solidified at 4 GPa High Pressure

High pressure solidification rules of Al-Mg alloy needs to be discussed further for its wide range of application. Microstructures and phases of Al-25wt% Mg alloy solidified at 4 GPa were studied by optical microscope,X-ray diffractmeter,energy dispersive X-ray spectroscopy and transmission electron microscopy( TEM). The microstructure evolution mechanism of Al-25Mg alloy under high pressure was analyzed. The result shows that the alloy consists of α-Al phase and Al 3 Mg 2 phase under normal pressure. However,only Al 12 Mg 17 phase forms without Al 3 Mg 2 phase at 4 GPa. In addition,Mg concentration in α-Al phase increases and that of the lattice constant also increases. The α-Al dendrite presents the broken arms under normal pressure, after high pressure solidification,the morphology of the dendrite tends to integrate and the size of the dendrite arms

Efficiency of Chalcone Compounds Inhibitors for Acid Corrosion of Al and Al-3.5Mg Alloy

Corrosion inhibition of Al and Al-3.5Mg alloy by organic compounds, namely chalcones in hydrochloric acid solutions has been investigated by rapid polarization technique and weight loss method. Polarization measurements show that, the inhibitors act cathodically both in case of Al and Al-3.5Mg alloy. It was found from the weight loss measurements that, the inhibition efficiency depends on the substituent in the chalcone compound. The relative inhibitive efficiency of these compounds has been explained on the basis of structure dependent electron donor properties of the inhibitors and the metal inhibitor interaction on the surface. The inhibition efficiency ranges from 16 to 64% for Al and from 30% to 91% for Al-3.5Mg alloy

Dynamic Mechanical Behavior and Microstructural Evolution of the Al-6Mg Alloy Subjected to Three Treatment Conditions

The mechanical properties of Al-6Mg alloy with three treatment states （H112, O and cold-extruded states） were investigated at room and high temperatures using an INSTRON machine and a Split Hopkinson Pressure Bar （SHPB）. Stress-strain curves of the alloy with different processes were obtained at a quasi-static strain rate of 5×10-4 s-1and dynamic strain rates of 1 400-4 200 s-1, respectively. The results suggest that, at room temperature, the three processed Al-6Mg alloys are all low sensitive to strain rate. The O state Al-6Mg alloy （Al-6Mg-O） exhibits the most ductility, while the cold-extruded Al-6Mg alloy （Al-6Mg-C） displays the highest strength. At elevated temperatures, the yield stresses and the differences in yield stress of the three processed alloys all decrease with increasing temperature under the quasi-static strain rate of 5×10-4 s-1. Based on test results, modified Johnson-Cook （JC） constitutive models for the three processed Al-6Mg alloys were developed. The microstructures before and after deformation were examined by electron backscattered diffraction （EBSD） and further dynamic recrystallization （DRX） at the strain rate of 3 300 s-1 was discussed.

Effects of conform continuous extrusion and heat treatment on the microstructure and mechanical properties of Al–13Si–7.5Cu–1Mg alloy

The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy,respectively.The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing.After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494℃for 1.5 h and aging at 180℃for 4 h,its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa.Its wear resistance was also enhanced.The factors leading to the enhanced strength,hardness,and wear resistance of the alloy were discussed in detail.

Microstructure and mechanical properties of Al-7Si-0.7Mg alloy formed with an addition of(Pr+Ce)

Effects of （Pr＋Ce） addition on the Al-7Si-0.7Mg alloy were investigated by optical microscope （OM）, energy diffraction spectrum （EDS）, X-ray diffraction （XRD） and tensile tests. The results showed that the Al-7Si-0.7Mg alloy was modified with （Pr＋Ce） addition. The needle-like eutectic silicon phase developed into rose form and the crystalline grains decreased in size and showed a high degree of spheroidization. When the amount of the （Pr＋Ce） addition reached 0.6 wt.%, the mean diameter was 31.8μm （refined by 50%）. The aspect ratio decreased to 1.35, and the tensile strength and ductility reached 192.4 MPa and 2.18%, respectively At higher levels of addition, over-modification occurred, as indicated by increased grain size and reduced mechanical properties. The poisoning effect of the （Pr＋Ce） addition on eutectic silicon and the constitutional supercooling caused by the （Pr＋Ce） addition were the major causes of alloy modification, grain refinement, and the improvement of mechanical properties.

轧制方式对工业包装铝合金板材微结构及各向异性的影响

为了获得工业包装用高强高韧铝合金材料,采用喷射成形快速凝固技术和大压下量轧制技术制备了Al-9Mg合金板材。采用透射电镜、扫描电镜(采用EBSD技术)和X射线衍射仪测定了挤压态和轧制态Al-9Mg合金板材的微结构及织构特征,并测试了板材的各向异性行为。试验结果表明:大压下量交叉轧制CBA促进了动态再结晶的发生,细化了晶粒组织,显著提高了大角度晶界的比例;与挤压态和AAA轧制方式相比较,CBA轧制方式显著降低了挤压态合金中典型的Brass织构{110}<112>的取向密度,在β取向线上CBA轧制态板材中的Brass织构取向密度最低,且板材中没有典型的织构特征;同时,CBA轧制态合金板材具有更好的深冲性能,在3个方向0°,45°和90°的力学性能基本一致,其室温拉伸强度和伸长率分别在592MPa和19.6%以上。