基于SIMA法的铝合金复杂构件触变锻造成形技术

采用半固态触变锻造技术成形铝合金构件,容易实现轻量化、低成本、短流程制造,因此在汽车、航空航天等领域应用广泛,但是对于高强铝合金复杂形状构件触变锻造存在半固态坯料制坯工序复杂、制件固液偏析严重和力学性能较弱等问题。基于SIMA制坯方法,提出了分级热处理、快速感应重熔和梯度等温处理等重熔工艺以及触变-塑变复合成形等新成形技术,优化了变形铝合金二次重熔半固态组织调控和触变锻造技术,获得了良好的半固态球晶组织并成形出合格的制件,最后提出了铝合金触变锻造成形中仍需解决的问题和发展方向。     

Induction heating of semisolid billet and control of globular microstructure to prevent coarsening phenomena

An important step in the thixoforming process is the induction heating of the raw materials to the semisolid state. Using this technology, the process behavior is satisfactory from the point of view of reproducibility and temperature control. Therefore, the objectives of this study are to define the correct relationship between coil length and billet length for uniform induction heating and to present the optimal reheating conditions suitable for the thixoforming process (or to secure a fine globular microstructure without liquid segregation). The optimal inductive coil on the induction heating process of semisolid billet machined to 76 mm diameter and 90 mm length to reduce the temperature gradient of the billet and to obtain the globular microstructure was theoretically designed and the suitability of the designed coil dimensions verified by reheating experiments. The globular microstructures of semisolid billet in heating and holding processes were controlled to prevent the coarsening phenomena of Al-7%Si-0.3%Mg alloy and to apply to the thixoforming process. In addition, the effects of the history of processing and induction heating parameters such as reheating time, holding time, holding temperatures, capacity of the induction heating system, and adiabatic material size on the globularization were investigated. It was concluded that in the case of a three-step reheating process, the final holding time is the most important factor and 2 min is suitable to maintain a globular microstructure.     

Constitutive Modeling for Thixoforming of 9Cr1 8 Semi-solid Alloy and 3D Forecast Mapping

Thixotropic compression tests were carried out on 9Cr18 semi-solid alloy through Gleeble-1500 thermal simulation machine.According to the experiment analysis,macro separation occurred during thixoforming.The liq-uid film was extruded outside to the surface and solidified to form eutectic structure.The solid particles were con-nected with each other and underwent plastic deformation.According to the comparison between Zhou-Guan model and modified Zhou-Guan model,it could be observed that the adding of thixotropic factor played an important role in the regression and the latter one was more credible.The modified Zhou-Guan model could well describe the thixo-forming behavior.3D forecast mapping was built for 9Cr18 semi-solid alloy in thixoforming temperature range.It would provide valuable information for selecting process parameters during thixoforming in the manufacture process.     

半固态触变成形制备高硅铝基电子封装盒体的组织与性能

利用半固态触变成形工艺制备高硅铝电子封装盒体,分析盒体中Si相的分布特征.采用金相显微镜和扫描电镜观察盒体不同部位的显微组织,并测定其热物理性能及力学性能.结果表明,Al-25％Si(质量分数)合金在半固态触变成形中Si相和液相产生分离流动,液相从盒体中流出,Si相在盒体中聚集,其体积分数从盒体底面向四壁逐渐降低.盒体底面中心和四壁的热导率分别为107.6和131.5W/(m.K),热膨胀系数分别为7.9×10-6和10.6×10-6 K,抗弯强度由167MPa缓慢增加至180MPa.组织和性能呈现梯度变化.     

The Rheological Behaviour of Metallic Suspensions

The knowledge of the rheological behaviour of metallic suspensions is an important issue when simulating die filling in thixoforming processes. Therefore rheological experiments like step‐change in shear rate tests, shear stress ramps and oscillation experiments have been carried out to characterise the flow behaviour of semi‐solid alloys exemplarily for A356 and Sn‐15%Pb. The material exhibits a yield stress and shows shear‐thinning and thixotropic flow behaviour, which is strongly influenced by the solid fraction, the particle shape and size and the degree of particle agglomeration. The instantaneous response on a change in shear rate was observed and pretends shear‐thickening properties. All experiments were carried out in a Couette rheometer. The experimentally gained data are well fitted to a model approach, which consists of a modified Herschel‐Bulkley law and accounts for the time‐dependent effects by introducing a structural parameter κ.     

A2017半固态材料制备与半固态成形的实验研究

应用单辊搅拌技术 (也称SCR技术 -Shearing CoolingRollProcess)制备出的A2 0 17半固态材料比常规铸造坯组织优良 ;SCR技术制备的A2 0 17半固态材料在 5 3 0℃～ 5 70℃范围内 ,可获得球形晶粒组织 ,可以进行半固态轧制成形 ;A2 0 17半固态材料触变过程分为四个阶段 ,在稳定触变阶段 ,并在 64～ 72 %的最大加工变形范围内 ,A2 0 17半固态材料的触变性能稳定     

Research on semi-solid thixoforming process of AZ91D magnesium alloy brackets for generators in JH70-type motorbikes

The investment on semi-solid die casting processes of AZ91D magnesium alloy brackets for generators in JH70-type motorbikes is introduced. The processes of low super-heat and cooling slope for the preparation of billets with non-dendritic microstructure, the remelting of billets for thixoforming and the parameters in the process of semi-sohd thixoforming have been researched. The results show that primary billets with non-dendritical structures can be prepared by forming great amount of nuclei in melt via the process of low super heat. By optimizing the remelting process through adjusting the current of the induced equipment, semi-solid billets with a structure of spherical grains were obtained from the primary billets with non-dendritical structure. The range of 580℃ to 583℃ is the proper remelting temperatures by which the billets have an expected thixotropy and can be transferred to a die-casting machine. The optimized parameters of semi-solid forming in a die-casting machine are as follows： the area of the ingate in the die is 383.5 mm^2, the speed of the pierce of the machine 5 m/s, the shot pressure of the pierce 75 MPa, and the maintenance pressure of the pierce 350 MPa. The castings of brackets for supporting generators in JH70 type motorbikes were formed by adopting the optimized processes and parameters mentioned above.     

树枝晶SiCp/ZA27复合材料部分重熔过程中的组织演变

用扫描电镜 (SEM )背散射成像技术对金属型铸造树枝晶SiCp/ZA2 7复合材料部分重熔过程中的组织变化进行了观察。结果表明 :在 460℃加热过程中 ,因晶界共晶组织向初生晶的扩散 ,造成树枝晶二次枝晶臂和晶粒间的快速合并 ,形成无明显晶界的组织 ,将分布于枝晶间的SiCp 裹入晶内 ,接着 ,剩余共晶组织开始熔化 ,组织发生分离 ,形成不规则的大块状组织 ,并将SiCp 返还于晶粒间的液相中 ,随后 ,因不规则组织突出部位 (曲率大 )的溶化 ,组织趋于圆整 ,最后经球状化形成尺寸较大的近球状颗粒。还从相变角度分析了组织的演变过程。     

Effects of Compression Parameters on Deformation Behaviors of Semi-Solid ZA27 Alloys

1　IntroductionZinc -basedalloyscontaining 8% - 2 7%alumi num ,1 % - 3 %copperandamarginalqualityofmagne siumhavebeenobservedtobepotentialmaterials,whichcouldbeeffectivelyandeconomicallysubstitutedinplaceofbronzes,aluminumalloys,castironsandsteelsforava rietyofengineeringapplications[1,2 ].Inspiteofanumberofmerits,suchasgoodcastability,mechanicalpropertiesandexcellentwearresistance,thealloyssufferfromporos ity,especiallyforZA2 7alloy,duetoitswiderangeofso lidificationtemperature[2 ].Inrecenty…     

Friction Stir Processing of Thixoformed AZ91D Magnesium Alloy and Fabrication of Surface Composite Reinforced by SiC_ps

The microstructural evolution characteristics of the thermomechanically affected zone (TMAZ) alloy during friction stir processing (FSP) of thixoformed (TF) AZ91D alloy were investigated. Simultaneously, a surface composite layer reinforced by SiC particles (SiCps) was prepared on the alloy by FSP and the corresponding tribological properties were examined. The experimental results indicate that dynamic recrystallization and mechanical separation (including splitting and fracture of the primary grains) are ...