Different grain refinement mechanisms of minor zirconium and cerium in magnesium alloys

Zirconium and rare earth element cerium were added in magnesium and magnesium alloys to study their different grain refinement mechanisms. The results show that zirconium has an obvious refinement effect on the cast grain of magnesium and its alloys without the alloy element Al because the crystal structure of zirconium is the same as magnesium matrix, and the lattice parameters are close to magnesium. Zirconium can decrease the grain size of magnesium from 150 to 20 pm. The rare earth cerium also has a grain refinement effect on Mg and Mg-Al alloy. The cerium atoms tend to remain in the liquid rather than solidify with the solvent atoms magnesium at the solid-liquid interface. The liquid constitutional undercooling can provide a heterogeneous crystal nucleation. The grain is refined from 200 μm to 40-80 μm. These two elements have different grain refinement mechalfism on Mg alloy. The mechanism of zirconium is that it acts as the nuclei of α-Mg. But the mechanism of cerium is that it increases the liquid constitutional undercooling that can provide a heterogeneous crystal nucleation for the alloy.     

熔体热速处理对铸造Mg合金组织和力学性能的影响

研究了熔体过热和热速处理对AZ91铸造Mg Al Zn合金组织和力学性能的影响。在含有Mn和钢坩埚内壁未刷有涂料的前提下 ,熔体温度 (82 0℃ )不够高时 ,会引起晶粒的粗化 ;熔体温度 (870℃ )足够高时 ,镁合金结晶晶核的增加引起了基体组织的细化 ,同时组织中的γ强化相比未高温过热时弥散、均匀 ;热速处理后组织部分保留了高温过热时的特性 ,从而使镁合金的力学性能和铸件质量得到提高。     

变形镁合金杯形件反挤压成形工艺研究

介绍了一种先进的超塑性反挤压成形新工艺,使用这种工艺将一个工业牌号的变形镁合金AZ31D的圆形坯料成形出一个杯形零件。成形后零件的几何尺寸精度完全满足工程需要无需任何机械加工。这种超塑性成形工艺使这种镁合金材料的微观组织和机械性能得到很大提高。材料的晶粒度由原始坯料的几百微米细化到了5～10微米,材料硬度由原始坯料的43HB提高到了57HB,硬度提高26．7％。文中介绍了试验过程,分析了这种超塑性成形提高材料组织性能的原因。     

Correlation of recalescence with grain refinement of magnesium alloys

The grain refinement of Mg-Al based alloys with carbon inoculation was investigated by a computer-aided cooling curve analysis(CA-CCA) system.The results show that carbon inoculation decreases the main parameters of the recalescence regime during the initial stage of solidification.These parameters include the recalescence undercooling(Δθ_(rec)),duration of recalescence (t_(rec)),and liquid peak parameter(LPP) which is firstly introduced into magnesium alloys.The resultant grain size decreases with incre...     

Mg对Al-Ti-B、Al-Ti-C中间合金细化铝晶粒效果的影响

试验研究了Mg对Al-5Ti-1B和Al-5Ti-0.2C两种中间合金细化铝晶粒效果的影响,分析了Mg影响两种中间合金细化铝晶粒行为的机制。结果表明,在w(Mg)=1%～7%的范围内,镁含量的增加,对两种中间合金细化铝晶粒的促进作用不显著,但对晶粒形貌有显著的影响;晶粒形貌取决于所用中间合金的种类和Mg添加量大小,相同镁含量时,用Al-5Ti-1B细化比用Al-5Ti-0.2C细化后晶粒的树枝化程度小;细化所用的中间合金相同时,随着镁含量的增加,细化晶粒的树枝化程度增大。     

镁及镁合金的晶粒细化

叙述了镁及镁合金晶粒细化的几种方法，如熔剂处理法、熔体过热法、熔体搅拌法、合金化细化晶粒、固态变形处理、半固态成形及快速凝固工艺等。细化镁合金晶粒尺寸能显著提高其力学性能，这对推广镁合金的应用具有重要意义。     

Effects of precipitation characteristics on the out-of-pile corrosion behavior of niobium-containing zirconium alloys

The effects of intermediate annealing temperature on the corrosion behavior of Zr−0.4Nb−0.8Sn−0.3Fe−0.2Cr−0.1Mn and Zr−1.5Nb−0.4Sn−0.1Fe alloys intermediate-annealed at various temperatures were investigated. The relationship between the corrosion behavior and the precipitation characteristics was discussed. A desirable microstructure containing a fine dispersion of second phase particles was obtained by intermediate annealing at a low temperature. Intermediate annealing at higher temperatures resulted in undesirable microstructural features including the precipitation of β-Zr and the coarsening of precipitates. The corrosion resistance of the alloys was apparently degraded with increasing size of the precipitated intermetallic compounds, especially in Zr−1.5Nb−0.4Sn−0.1Fe where β-Zr precipitated on higher-temperature annealing. The corrosion behavior of Zr−1.5Nb−0.4Sn−0.1Fe was more sensitive to intermediate annealing temperature than was that of Zr−0.4Nb−0.8Sn−0.3Fe−0.2Cr−0.1Mn. An examination of particle size distribution revealed that the corrosion behavior of the alloys was dominantly affected by β-Zr larger than the specific size, which is responsible for the difference in corrosion resistance between Zr−0.4Nb−0.8Sn−0.3Fe−0.2Cr−0.1Mn and Zr−1.5Nb−0.4Sn−0.1Fe. It is implied from these results that the optimum corrosion performance of niobium-containing zirconium alloys is achieved by maintaining a uniform distribution of fine second phase particles.     

Microstructures and mechanical properties of hot rolled AZ31 Mg alloy sheets

The microstructures and mechanical properties of hot rolled AZ31 Mg alloy sheets were studied to understand the microstructure evolution during AZ31 Mg alloy hot rolling process. The roller was heated to 180 ℃ with burning hydrogen, and the extruded plates were rolled at 400 ℃ from 10 to 1 mm with a reduction of 30% in thickness per pass. The result shows that there is no side-cracking of these rolled sheets every pass. The extruded microstructures are greatly refined and mechanical properties are improved. The fine grains of about 4μm were obtained of the final 0.9 mm sheets.     

Effect of nitrogen addition on microstructures and mechanical propeties of TiAl based alloys

1INTR0DUCTI0NTheTiAlbasedalloyhasbeenknownt0beoneofthemostpromisingcandidatesforhigh-temperaturestructuralapplications['J.Thepr0p-ertiesofthealloysstronglydependedontheir'[z]Ithasbeenthoughtthatthemicrostructures.IthasbeenthoughtthatthefinefullylamelIarmicrostructurehadthebestcombinationofmechanicalproperties['].In0r-dertorefinethecoarsefullylamellarmicrostruc-tureincastcondition,thermomechanicaltreat-ments(TMTs),includingh0textruding,hotrollingandisothermalforging,havebeenused;butbecau…     

固溶态Mg-Gd-Zr合金的组织与力学性能

使用半连续铸造法制备Mg-xGd-0.6Zr(x=2,4,6,质量分数)镁合金,研究不同Gd含量对Mg-xGd-0.6Zr合金组织与力学性能的影响,优化Mg-6Gd-0.6Zr合金的固溶处理工艺.采用光学显微镜、X射线衍射仪、扫描电子显微镜、能谱仪和显微硬度仪对合金的组织和力学性能进行表征.结果表明,随着合金中Gd含量的增加,晶粒尺寸略减小:Mg-xGd-0.6Zr合金的显微硬度与Gd的摩尔浓度呈线性关系.在铸造过程中由非平衡凝固形成的Mg2Gd和Mg3Gd在固溶处理时将转变成Mg5-05Gd平衡相;当固溶温度超过460℃时,Mg<,5.05>Gd溶解到a-Mg中.Mg-6Gd-0.6Zr合金的优化固溶处理工艺为(300℃,6 h)+(460℃,10 h).     

Hereditary effect of Al-based modifiers and grain refiners on structure and properties of A356.2 alloys

The hereditary effect of Al-Ti, Al-Ti-B, Al-Sr master alloys on the structure and properties of A356.2 alloys was investigated, and comparison analysis between the master alloys used in the foundry industry and the fine-crystalline grain refiners produced by technologies of Samara State Technical University was conducted. The results show that less than 0.5% additions of FCR master alloys can promote 8%-20% in the elongation of as-cast A356.2 alloys. FCR additives are more efficient in comparison with conventional grain refiners and modifiers. Their effectiveness depends on their genetic effect of their finer structures.     

Mg-Gd-Y-(Mn, Zr)合金的显微组织和力学性能

采用溶剂保护方法制备了合金Mg-9Gd-4Y-0.65Mn和Mg-9Gd-4Y-0.6Zr,并挤压成棒材。通过光学显微镜、X射线衍射仪、扫描电镜和透射电镜等分析研究了这两种合金铸态和变形态的显微组织和力学性能。结果表明:铸态含Mn合金的晶粒粗大,而含Zr合金的晶粒细得多,Zr能有效地细化Mg-RE合金的晶粒;热变形加工使两种合金的晶粒度大大减小,拉伸强度大幅提高,在同等加工条件下,含Mn合金形变细化晶粒作用更显著;两种变形合金都有非常高的室温和300℃高温强度,但含Mn合金的延伸率较高;含Zr变形镁合金适宜通过T5处理,而含Mn变形镁合金适宜通过T6处理提高其综合拉伸力学性能。     

Microstructure formation and grain refinement of Mg-based alloys by electromagnetic vibration technique

The microstructure formation and grains refinement of two Mg-based alloys, i.e. AZ31 and AZ91D, were reported using an electromagnetic vibration （EMV） technique. These two alloys were solidified at various vibration frequencies and the microstructures were observed. The average size of grains was quantitatively measured as a function of vibration frequencies. Moreover, the grain size distribution was outlined versus number fraction. A novel model was proposed to account for the microstructure formation and grain refinement when considering the significant difference of the electrical resistivity properties of the solid and the liquid during EMV processing in the semisolid state. The remarkable difference originates uncoupled movement between the mobile solid and the sluggish liquid, which can activate melt flow. The microstructure evolution can be well explained when the fluid flow intensity versus vibration frequency is taken into account. Moreover, the influence of the static magnetic field on texture formation is also considered, which plays an important role at higher vibration frequencies.     

Grain refinement and mechanism of CAl_（0.5）W_（0.5） compound in Mg-Al alloys

The effect of CAl0.5W0.5(CAW) compound on the grain refinement of Mg-Al based alloys was investigated.The results show that CAW compound is an effective and active grain refiner.The grain size of binary Mg-Al alloys is more than 500 μm,and it is changed to about 110 μm with a 1 wt.% CAW addition.The hardness increased with the decease of grain size monotonously.The mechanical properties are improved by the addition.The fine grain size is mainly ascribed to the dispersed Al2CO particles,which are very potent nucleating substrates for Mg-Al alloys.The nucleation cores formed by chemical reaction directly are well-distributed in the matrix.     

Effect of Ce addition on microstructure of Mg–9Li alloy

The as-cast and as-extruded Mg–9Li, Mg–9Li–0.3Ce alloys were respectively prepared through a simple alloying process and hot extrusion. The microstructures of these alloys were investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). The results indicate that Ce addition produces a strong grain refining effect in Mg–9Li alloy. The grain size of the as-extruded alloy reduces abruptly from 88.2 μm to 10.5 μm when the addition of Ce is 0.36%. Mg₁₂Ce is verified and exists inside the grains or at the grain boundaries, thus possibly pins up grain boundaries and restrains the grain growth.     

Forming of magnesium alloys at 100 °C by hydrostatic extrusion

Magnesium wrought alloys are of special interest for use as structural parts due to the possibility of obtaining improved and more homogeneous microstructure and mechanical properties compared with cast components. The market for magnesium wrought alloys is still relatively small, and they are only used for special applications due to the high cost of the feedstock. Currently, with the decreasing prices for the primary magnesium extrusion, magnesium has become competitive with aluminum, and is important for upcoming research and development activities. In this study hydrostatic extrusion, as a quite rarely applied technique, was used for deformation of commercial magnesium alloys at 100 °C, which is significantly below the temperature necessary for activation of new gliding systems. All experiments were carried out using typical industrial extrusion parameters like extrusion rate and extrusion ratio but with the objective of obtaining extremely fine-grained materials as are received typically from equal channel angular extrusion processing. These experiments show that the processing of magnesium alloys is possible even at a temperature of 100 °C. The limitations of this processing and the influence of process parameters on the microstructure and mechanical properties of extruded profiles will be discussed.     

含锆铝合金的力学性能和强化机理

研究了高强铝合金的力学性能与Zr含量的关系，计算了合金的各种强化因素值。研究发现：合金的抗拉强度巩和屈服强度如σ0.2均随Zr含量的增加而增大，增幅分别达到11．8％和12．6％；合金延伸率δ在Zr添加量不高时随Zr含量的增加而增大，在Zr含量为0．06％时出现峰值，随后合金延伸率δ逐渐稳定在8％左右。结合合金显微特征，合金强化机理主要包括晶粒细化、颗粒弥散强化及形变强化，在Zr含量为0．16％的合金中相应的强化值分别为21.35和14MPa.     

Ce对镁及镁合金中晶粒的细化机理

研究了Ce对镁及镁合金晶粒细化效果和力学性能的影响。结果表明：纯镁结晶时易形成粗大的柱状晶和扇形晶，加入微量稀土元素Ce后，晶粒被明显细化，柱状晶全部转化成等轴晶。在AZ31合金中添加微量稀十元素Ce，晶粒由未细化前的约300μm下降到约30μm。稀土Ce在镁及AZ31合金中的固溶度很小，在凝固过程中固／液界面前沿Ce容易富集引起成分过冷形成新形核带导致晶粒细化。凝固过程中溶质再分配造成固液界面前沿成分过冷度增大是稀土元素细化镁及镁合金的主要机理。     

Review of grain refinement methods for as-cast microstructure of magnesium alloy

As the lightest structural metal, Mg and Mg-based alloys have great potential applications in the aerospace, automotive and nuclear industries. However, such applications have been limited by low ductility and strength. Theoretically, small grain sized structure can synchronously improve its ductility and strength. Yet,universally reliable grain refinement techniques for the magnesium alloys are still under investigation and some are in strong debating. This paper presents a brief review of development of grain refinement methods for magnesium alloys, which would contribute to a better understanding of the factors controlling grain refinement and provide an outlook of future research in this field.