Reheating microstructure of refined AZ91D magnesium alloy in semi-solid state

By means of equal channel angular extrusion (ECAE) test, upsetting test and metalloscope, reheating microstructures of raw casting ingots, materials prepared by SIMA and materials extruded by ECAE in semi-solid state were investigated. The results show that compared with those of raw casting ingots and materials prepared by SIMA, reheating microstructure of materials extruded by ECAE is the best and the final grain size is the finest. With increasing holding time, a growing phenomenon occurs in reheating microstructure of materials extruded by ECAE, which can be described by Ostwald ripening law. The average grain size increases firstly, subsequently decreases and the shape factor of grains approaches to 1 as the reheating temperature increases. With increasing equivalent strain, the average grain size decreases. This demonstrates that reheating material extruded by ECAE technology is a good method to prepare AZ91D magnesium alloy semi-solid billets.

Isothermal grain growth of reactive spray formed 7075 alloys in semi-solid state

The grain growth behavior in reactive spray formed 7075+2.91 vol percent TiCAl alloy was studied and compared with that of spray formed 7075 Al alloy at semi-solid state. Theeffects of in-situ TiC particles on the microstructure of spray formed 7075 Al alloy were alsoinvestigated. The specimens were heat-treated isothermally at various temperatures between thesolidus and liquidus of 7075 Al alloy for times in the range of 10-60 min, then quenched in water.The microstructure of reheated specimens was characterized using scanning electron microscopy andoptical microscopy. The grain size was measured using a mean linear intercept method. Results showthat the in-situ TiC particles can effectively retard grain growth and refine the grain at a limitedsize. The grain growth exponent in Arrhenius equation increases from 2 to 3, which indicates thatthe in-situ TiC particles have the significant pinning effect on grain coarsening in the semi-solidstate.

Structure of miniature components from steel produced by forming in semi-solid state

To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconventional innovative technological procedures.One of these technologies is the forming in semi-solid state involving rapid solidification of miniature components from steels.Production of such components is complicated by a number of technical problems.To explain phenomena of the process and structure development,the production of miniature components from the tool steel X210Cr12 difficult to form was experimentally tested.The structure of this originally ledeburite steel consisted of 95 % of metastable austenite after the treatment.Metastable austenite was located particularly in globular and polygonal grains while the remaining interspaces were filled by lamellar network.The detected high stability of extremely high fraction of metastable austenite was tested under different conditions of thermal exposition and mechanical loading.

Thixoforming of SiC ceramic matrix composites in pseudo-semi-solid state

A new forming process, ceramic matrix composites thixoforming in pseudo-semi-solid state, was proposed based on powder metallurgy technology combined with the semi-solid metal forming process. The satellite angle-frames were prepared by this technology with Al_p and SiC_p materials mixed with different volume fractions. It is proved that it is feasible for the forming of the ceramic matrix composites by this technology through metallographic analyses and tensile tests. The results also show that the microstructures of samples are homogeneous and they have high hardness and certain plasticity.

Rheological behavior of Al_2O_ 3n/Al_μ composite in pseudo-semi-solid state

A new technology for ceramics matrix composites-ceramics matrix composite thixoforming in pseudo-semi-solid state based on semi-solid metal process and powder metallurgy technology were proposed. The rheological behavior of Al2O 3n/Alμ composite was studied by isothermal compression in pseudo-semi-solid state. The variation rules of the true stress-true strain, rheological behavior and the influencing factors were also analyzed. The results show that the flow stress decreases evidently with the increasing pseudo-semi-solid temperature, and that the trend of the true stress-true strain curve of the composite in pseudo-semi-solid state can be divided into four stages: increase, decline, re-increase and re-decline.

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

An investigation was performed on the effects of semi solid compression parameters,such as strain rate,compression temperature and heating time at these temperatures on deformation behaviors of two kinds of ZA27 alloys,one was modified by Zr and the other was unmodified.The results indicate that with the increasing of the strain,the stress of the modified composite first sharply increases to a peak value,then dramatically decreases to a plateau value,and again increases till the end of deformation.But for the unmodified,after being up to a peak value,the stress only decreases slowly.As the compression temperature or the heating time decreases,or the strain rate increases,the stress level and the cracking degree of these two kinds of alloys increase.Under the same deformation conditions,the stress level and the cracking degree of the unmodified alloy are higher than those of the modified one.But there is an exception that the stress level of the unmodified alloy is minimum and smaller than that of the modified one when deformed at the low temperature of 450℃.These phenomena were mainly discussed through analyzing the microstructures under different conditions and the deformation mechanisms at different deformation stages.

Effects of holding temperature and time on semi-solid isothermal heat-treated microstructure of ZA84 magnesium alloy

The feasibility of fabricating ZA84 magnesium alloy with non-dendritic microstructure by a semi-solid isothermal heat treatment process and the effects of holding temperature and time on the semi-solid isothermal heat-treated microstructure of the alloy were investigated. The results indicate that it is possible to produce ZA84 alloy with non-dendritic microstructure by suitable semi-solid isothermal heat treatment. After being treated at 560-575 ℃ for 120 min, ZA84 magnesium alloy can obtain a non-dendritic microstructure with 14.2%-25.6% liquid fraction and an average size of 56-65 μm of the unmelted primary solid particles. With the increasing holding time from 30 to 120 min or holding temperature from 560 to 575 ℃, the average size of unmelted primary solid particles decreases and globular tendency becomes more obvious. Under the experimental condition, the microstructural evolution of ZA84 alloy during semi-solid isothermal treatment is mainly composed of three stages of initial coarsening, structural separation and spheroidization. The subsequent coarsening of spheroidal grains is not observed.

Effect of predeformation on semi-solid microstructure of ZK60+RE magnesium alloy

Microscopical techniques were used to provide the semi-solid microstructure evolutions of ZK60+RE alloys formed by compression and equal channel angular extrusion(ECAE), respectively. It is found that after compression and ECAE, as-cast microstructures exhibit an obvious directional characteristic. The predeformation exerts a significant influence on the formation of thixotropic microstructures during partial remelting. Coalescence and Ostwald ripening are operative in the semi-solid mixture for both compression and ECAE formed alloys. Furthermore, the degree of spheroidization of ECAE formed alloy is better than that of compression formed alloy in appearance.

Structural evolution of ZA27 alloy during semi-solid isothermal heat treatment

The structural evolution of ZA27 alloy modified by element Zr was studied during semi solid isothermal heat treatment, and its transformation mechanism was also discussed. The results indicate that the primary α phase changes from equiaxed grains to spherical grains gradually at semi solid temperature of 460 ℃. With increasing isothermal time, the eutectic between boundaries of α phase diffuses toward α phase, and the primary equiaxed grain arms merge and boundaries tend to disappear to form near particle grains. Further, the eutectic left on α boundaries melts to make the near particle grains separate, and form spherical structure at last. [

Effect of deformation temperature and strain rate on semi-solid deformation behavior of spray-formed Al-70%Si alloys

Spray-formed Al-70%Si(mass fraction) alloys were deformed by compression in the semi-solid state. The effects of the deformation temperature, strain rate and the microstructure were studied. Two strain rates(1s -1and 0.1s -1) and six deformation temperatures (600℃, 720℃ , 780℃, 900℃, 1000℃ and 1100℃) were chosen. The stress—strain curve exhibits a peak at low strain and then decreases to a plateau before it starts to increase again as the strain increases. The stress required for deformation at lower strain rate and at higher deformation temperatures is less than those at higher strain rate and at lower deformation temperatures. Four mechanisms of semi-solid deformation can be used to explain the different behaviors of the stress—strain curves under different conditions.

Microstructure Evolution of Semi-solid Processed Hyper-eutectic Al-30%Si Alloy

An investigation was made on the influences of mechanical stirring on microstructure of hyper-eutectic Al-30%Si alloy (inmass fraction) during solidification. The primary Si crystals formed in the alloy melt were gradually changed from elongated platelets tonear-spherical shapes by mechanical stirring. The spheroidization of primary St crystals occurs by the mechanism of bending and fractureof Si platelets, wear and collision between Si crystals, and coalescence of small Si particles. The influence of under-cooling and coolingrate of the alloy melt on primary Si crystals of semi-solid processed alloys is investigated as well. The increase of under-cooling andcooling rate decreases the size of primary Si crystals.

Microscopic characterization of semi-solid aluminium alloys

The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 （θ phase） precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformatinn temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.

半固态A356-0.4%Gd合金制备过程的电磁场模拟与试验研究

通过数值模拟研究了半固态A356-0.4%Gd合金熔体中磁感应强度和电磁力的分布,并分析了电流强度和电流频率对其的影响。模拟结果表明:磁感应强度及电磁力由熔体中心沿半径方向逐渐增大,呈“中间小,边缘大”分布,且增大电流强度及频率能明显增大合金熔体边缘区域的磁感应强度及电磁力,合金熔体整体得到充分搅拌的关键在于其边缘区域的电磁力。基于数值模拟结果,结合试验,进一步探明电流强度及频率对合金铸坯中心与边缘区域处初生α相的影响。试验结果表明:在电磁场作用下,铸坯边缘位置的初生相形貌与尺寸皆优于中心位置;当合金熔体于650℃浇注,在搅拌电流5 A、频率30 Hz下搅拌15 s,590℃下保温10 min后,其合金初生相在整体上较为均匀,且形貌最佳。

基于特征增稳的混合固态激光雷达目标检测

稳定的点云特征提取对激光雷达三维目标检测至关重要。针对现有深度学习算法仅能处理机械旋转式激光雷达点云数据,而对混合固态激光雷达数据支持不足的问题,本文基于IA-SSD搭建了适用于混合固态激光雷达的目标检测模型。首先,在点云编码前端添加了Cloth Simulation Filtering(CSF)用于地面次优点过滤;其次,利用局部特征融合和全局双线性正则化层组成的注意力机制,从局部和全局共同推动点云几何信息与特征信息融合;再次,利用GhostGConv替换原有低效的逐点卷积,通过通道混洗机制加强点云的特征交互,构建了增强型特征提取网络。最后,在点检测器IA-SSD中整合了上述模块完成模型构建。在混合固态激光雷达数据集SimoSet开展的验证结果表明,所提出的方法显著优于SimoSet数据集支持的其他算法精度指标;在KITTI数据集中等难度检测中,所提方法将IA-SSD三分类平均检测精度分别提升了1.17、1.47、0.5百分点。

Strengthening and toughening forming of Al/Al_2O_3 composite in pseudo-semi-solid state

A new technology thixo-die-forging of the composite in pseudo-semi-solid state was proposed based on the powder metallurgy technology combing with semi-solid metal process, and the cup shells with Al/Al2O3 composite was prepared successfully. The metallographic analysis and performance test show that the microstructure of parts is dense and mechanical properties axe excellent with the volume fraction of Al is 37%. The bend strength and fracture toughness of the composite are about 570- 690 MPa and 8.5-16.8 MPa·m^1/2, respectively. Comparing with reaction in situ and high temperature oxidation technologies the bending strength and fracture toughness are improved greatly. At the same time, it shows that the technology parameters have great influences on the properties. So it is feasible to prepare metal/ceramics composites by the proposed technology.

预变形及液固两相区等温处理对ZA27合金铸态组织的影响

研究了固液两相区等温处理对铸态ZA2 7合金初生相形貌的影响。结果表明 :在固液两相区进行等温处理时 ,枝晶熔断受固液界面处原子的扩散控制 ,提高等温温度、延长等温时间因有利于Zn和Al原子的扩散而促进初生相由枝晶向颗粒状晶演变 ;预变形促进初生相形貌演变的根本原因在于等温处理时液相沿预变形产生的亚晶界的熔渗。

浇注温度对自孕育铸造法制备AM60镁合金半固态浆料的影响(Ⅰ)

采用新型的自孕育法制备AM60镁合金半固态浆料,研究浇注温度对自孕育法制备AM60镁合金半固态浆料的影响。结果表明:随着浇注温度的降低,组织中发达和粗大的树枝晶逐渐减少;在接近液相线温度时出现小块状或蔷薇状晶粒,晶粒的尺寸逐渐减小;分布逐渐趋向正态分布,且存在一个合适的温度加工区间,即630～680℃,对应的晶粒尺寸为58.4～63.1μm。加入的孕育剂在熔体中起到内冷铁作用,加快熔体的冷却速率,使熔体快速到达半固态区间。采用自孕育法制浆时,合金熔体中晶核主要来源于熔体中的高熔点质点(Al8Mn5)、孕育形核和晶粒游离与增殖。

原始组织对半固态AZ91D镁合金重熔行为的影响

采用水淬法研究了具有5种不同凝固组织的AZ91D镁合金半固态熔化过程的行为。结果表明:增加冷却速率、预变形处理和晶粒细化有利于初始凝固组织中存在的非平衡组织的分散细化。原始组织中的非平衡共晶组织在加热过程中大部分扩散溶解而溶入基体中,剩余部分在加热过程中首先熔化;冷却速率越大或预变形处理以后的试样在熔化过程中更容易发生二次枝晶臂之间的合并。提出半固态熔化过程可分为成分均匀化、共晶熔化及部分初生相的熔化和球化完成3个阶段,不同熔化阶段的控制性因素不同。熔化后的半固态组织中固态颗粒的尺寸和形貌主要与初始组织的形貌、加热过程中非平衡组织的溶解速度及加热速度有关。

半固态喷射沉积TiC_p／7075铝合金的晶粒长大规律

采用原位反应喷射沉积法制备TiC_p／7075半固态铝合金坯料,在600℃保温10—60 min,研究半固态二次加热过程中合金的晶粒长大规律,并与喷射沉积7075铝合金进行对比分析,结果表明,添加原位TiC颗粒后,合金的晶粒长大指数由2增加到3,晶粒长大速率明显减慢,其原因是添加TiC颗粒后合金晶粒长大激活能增加1倍左右,使得合金的晶粒长大更加困难,显示出原位TiC颗粒对喷射沉积7075铝合金的晶粒长大具有显著的抑制作用。

添加0.5%富铈混合稀土AZ91D镁合金半固态组织的形成

半固态浆料的固相颗粒尺寸、形态和分布主要取决于熔化过程中液相的形成与演化过程。采用添加0.5%富铈混合稀土来改善AZ91D镁合金的铸态组织,研究在半固态等温热处理中的组织演变以及非枝晶组织制备与控制的机理。结果表明:稀土合金化处理可促进初生相在等温热处理过程中由枝晶向粒状晶的转变,可获得更加细小、均匀的球状固相颗粒,并且其粗化速度较慢。半固态等温热处理过程中,整个系统处于熔化和结晶的动态平衡,铸态组织中枝晶根部高溶质浓度区或系统的温度、浓度起伏是固相颗粒内液相形成的内在和外在条件。