Effects of ultrasonic treatment on the tensile properties and microstructure of twin roll casting Mg-3%Al-1%Zn-0.8%Ce-0.3%Mn (wt%) alloy strips

Twin roll casted Mg-3%Al-1%Zn-0.8%Ce-0.3%Mn alloy strips with thicknesses of approximately 3.6-4 mm are prepared, and the effects of ultrasonic treatment on their tensile properties and microstructure are investigated. The results show that, after treatment with an ultrasonic power of 800 W, the grain size of α-Mg decreased from 136.3 μm to 44.7 μm, and the morphology changed from dendritic to globular. Grain multiplication by fragmentation of dendrites and cavitation-induced heterogeneous nucleation are the mechanisms of refinement of the α-Mg grains by ultrasonic treatment. The needle-like shaped intermetallic MgAlCeMn is modified by ultrasonic treatment and obtains a more globular shape with finer particles. This change was a result of undercooling created by the cavitation of ultrasonic treatment. This improved microstructure contributes to an increase in both tensile strength and elongation of twin roll casting magnesium alloy. The yield strength of the experimental alloy strips subjected to 800 W ultrasonic treatment is approximate 30% higher than that of alloy without ultrasonic treatment. Furthermore, the elongation of experimental alloy is almost double that of alloy without ultrasonic treatment. The relationship between the yield strength and the refined grain size of the experimental alloy can be expressed by the Hall-Petch equation σ_y = 74.8 + 31.4 × d^−1/2.     

微量Nd的添加对Mg-Al-Zn合金微观组织和高温力学性能的影响

分析研究了微量Nd的添加对Mg-Al-Zn合金显微组织和高温力学性能的影响.结果表明:Nd的加入,显著细化了合金的铸态组织,同时出现了新相Al3Nd化合物.当Nd添加量为1.0%时,可使铸态Mg-8.5Al-0.5Zn合金在150℃高温下的抗拉强度达到最大值为160MPa,和未加入Nd的合金相比提高了13.2%.     

Microstructural evolution of twin-roll cast Mg–3Al–0.5Mn–0.2Mm alloys during warm rolling and subsequent annealing

Microstructure of twin-roll casted (TRC) Mg–3Al–0.5Mn–0.2Mm (or AM30 + 0.2Mm) alloy strips consisted of columnar dendrites in the surface and equiaxed dendrites in the center regions, as well as widely dispersed fine primary intermetallic compounds located in the interdendritic region. Warm rolling of the TRC strips developed both deformation or shear bands and homogeneously dispersed fine particles. No evident dynamic recrystallization (DRX) was found in the TRC sheets during warm rolling. The dispersed fine particles seemed to retard DRX. The warm-rolled TRC sheets showed equiaxed fine grains with an average size of around 8 μm after annealing at 350 °C for 60 min. The TRC sheets had superior yield and tensile strengths to ingot cast (IC) samples. Elongation was similar to both TRC and IC samples.     

镁合金的双辊板带连续铸轧技术

综述了绿色环保材料镁合金的特点、适用范围及其加工方式,分析了镁合金双辊板带连续铸轧技术是镁合金加工的未来发展方向,并指出了存在的问题和挑战.     

超声波作用下双辊铸轧镁合金板带材的力学性能和成形能力

研究了超声波对双辊铸轧的Mg-3wt%Al-1%Zn-0.8?-0.3%Mn合金板带材组织和性能的影响。实验结果表明：超声波辅助镁合金的铸轧可以提高镁合金带材的强度、延伸率和极限深拉比值,在250℃镁合金带材的极限深拉比值可以达到2.16。这些镁合金力学性能和成形能力的提升是由于超声波铸轧过程中,超声波可以细化镁基体的晶粒尺寸,并同时对合金中的Mg17(Al,Zn)12和AlCeMn相起到变质作用。当超声波强度达到800W时,镁基体的晶粒尺寸可以从150μm细化到30μm,而且针状的AlCeMn相可以被变质成球状,从而提高了镁合金的力学性能和成形能力。     

真空吸注A356铝合金组织及性能研究

以A356铸造铝合金为研究对象,考察了该合金在真空吸注下的凝固组织、热处理组织及力学性能.结果表明,真空吸注使得凝固组织由常规条件下的粗大树枝晶转变为细小等轴晶,共晶硅由粗大杆状或针状转变为长度约为2～7 μm的板片状;T6热处理后,常规铸造与真空吸注组织内的共晶硅均发生粒化和球化过程,但真空吸注条件下共晶硅尺寸更为细小,在α-A1基体上分布更加均匀,两种组织的析出相Mg2 Si形状相似,均呈长度约400 nm的棒条状.随真空吸注的进行,拉伸试样的断裂形式由常规条件下的脆性断裂转变为脆性断裂与韧性断裂并存的混合模式,其抗拉强度、屈服强度、硬度和伸长率分别提高了12.5％、8.9％、87.3％和19.8％.     

Twin roll strip casting of high strength Al alloys with high solute contents using asymmetric nozzle

We investigated the feasibility of producing high strength Al alloy sheets with high solute contents using a twin roll strip caster equipped with an asymmetric nozzle. The combination of twin roll casting and the asymmetric nozzle used in this study reduced centreline segregation and hot tear, thereby increasing the casting speed. These features of the strip casting allowed the dissolution of more solute elements, suggesting the potential development of high strength Al alloys with a range of Mg contents up to 10 wt-%. The workability and mechanical properties of the cast strips were also evaluated to assess the feasibility of producing high strength Al alloy sheets superior to the present limit of conventional techniques.     

Heat treatment of vacuum high pressure die cast magnesium alloy AZ91

Alloys produced by high pressure die casting (HPDC) are generally considered non-heat treatable because trapped gas pores tend to expand, causing surface blistering and bulk distortion. In this paper, vacuum assisted HPDC of magnesium alloy AZ91 was used, and the properties were assessed. The specimens produced using vacuum die casting contain less porosity. Little improvement in yield strength by applying vacuum is found, although a small increase in elongation is observed. A conventional heat treatment applied to the vacuum die cast AZ91 shows pronounced precipitation hardening during aging, especially after a prior solution treatment. However, an associated improvement in yield strength after aging is not observed, and this is related to the decreased contribution of the ‘skin’ effect as a result of grain growth.     

Sn effect on microstructure and mechanical properties of ultrafine eutectic Ti–Fe–Sn alloys

Microstructural investigations on ultrafine eutectic (Ti₆₅Fe₃₅)_100−xSn_x alloys with x = 0, 1 and 3 at.% reveal that additional Sn is effective to control formation of the micron-scale dendrites and to decrease the length-scale of lamellar spacing with enhancing macroscopic plasticity at room temperature compression. Hence, it is possible to understand the influence of the microstructural change on the plasticity of the ultrafine eutectic Ti–Fe–Sn alloys.     

Development of a New Hot-cracking Test for Aluminium Alloys

A new hot-cracking test has been developed for aluminium alloys which allows investigations of hot-tearing to be carried out under well-controlled solidification conditions. The stress which develops in the solidifying ingot is perpendicular to the macroscopic growth direction and so columnar structures are tested normal to the growth axis of the columnar grains. A localised hot-spot must be imposed on the system if a macroscopic hot-tear is to form. Temperatures were recorded at various locations in the solidifying ingot so that the build-up of fraction solid could be monitored. The hot-cracking susceptibility of Al-Cu alloys has been investigated as a function of alloy composition and maximum susceptibility occurred in the range 0.5–2.0 wt% Cu. At a fixed composition of 6 wt% Cu, the grain structure/type was found to greatly influence cracking susceptibility as measured by this test. Hot-tears were always intergranular.     

Mechanical Property and Microstructure of Oxide Dispersion Strengthened Nickel-base Superalloy MA758

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Fabrication and mechanical properties of ultrafine grained WC-10Co-0.45Cr3C2-0.25VC alloys

The ultrafine grained WC-10Co-0.45Cr₃C₂-0.25VC alloys were fabricated through planetary ball milling and low pressure sintering. The effects of the cobalt particle size, milling speed and sintering temperature on the microstructure, hardness and fracture toughness of the ultrafine grained alloys were investigated using optical microscopy, scanning electron microscopy and mechanical testing. The results showed that the mechanical properties of the low pressure-sintered alloys substantially depend on the milling speed and sintering temperature. At the same time, the hardness and fracture toughness of the samples can be increased from 1703 MPa and 8.90 MN m^−3/2 to 1789 MPa and 11.21 MN m^−3/2, respectively, when the cobalt particle size is reduced from 17 μm to 1.4 μm.     

机械搅拌对半固态ZA27合金组织和性能的影响

研究不同等温温度、搅拌速度、搅拌时间等工艺参数对半固态ZA2 7合金力学性能和组织的影响 ;结果表明ZA2 7合金等温搅拌温度在 470℃～ 480℃ ,搅拌 10min～ 15min时 ,获得的性能和组织较好 ,搅拌强度越高 ,搅拌后获得的组织和性能越好。     

Ti—Al二元合金的成分对组织和力学性能的影响

用金相、扫描电镜和X射线衍射研究了6种不同Al含量Ti-Al二元合金铸态和退火态的组织结构和相组成的特征和变化。从结晶动力学的观点,分析了合金的结晶凝固过程。采用三点弯曲方法研究了合金的抗弯性能同Al含量的关系。结果表明,Al含量为34 wt%,经1100℃/30 h退火的合金抗弯性能最好,Al含量偏离34wt%,都对合金的力学性能不利。     

Mechanical Property and Microstructure of Oxide Dispersion Strengthened Nickel－base Superalloy MA758

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Effect of position on the tensile properties in high-pressure die cast Mg alloy

Tensile tests were performed at different locations of high-pressure die cast (HPDC) Mg alloy and the effect of position on the tensile properties such as yield strength (YS), ultimate tensile strength (UTS), ductility and fracture strain (FS) are explained. Additionally, the significance of micro-failure mode of the material is presented. The average size, area fraction and clustering tendency of pores and Mg₁₇Al₁₂ (β) particles as well average grain size are correlated with the mechanical properties and found their influences.