双向间歇电磁搅拌对半固态A356-Ce合金凝固组织的影响

利用强剪切强对流的双向间歇电磁搅拌技术与低过热度浇注技术复合工艺作用合金熔体,制备了凝固显微组织形貌为晶粒尺寸细小、形态规则圆整的半固态A356-Ce合金铸锭,研究了在磁场作用时间恒定15 s时铝合金熔体施加不同磁场频率、间歇时间对合金中初生α相晶粒尺寸和形貌演变方式的影响规律。结果表明,在合理的试验磁场频率和间歇时间范围内,随着磁场频率和间歇时间增加,初生相的尺寸逐渐细化、圆整度和分布均匀性增大。在磁场频率30 Hz、间歇时间3 s电磁搅拌工艺条件下半固态初生相的晶粒尺寸细化和球化程度达到最佳,组织中初生晶粒均匀分布,初生相的形貌由初始发达粗大的树枝晶向细小圆整的球状非枝晶转变,其平均等积圆直径处于各磁场频率和间歇时间作用下的最小值35.2μm;平均形状因子达到了峰值0.81。采用该复合工艺可制备出满足流变成形需要的优质的流变浆料。     

筒体温度对微熔铸半固态熔体A356晶粒形貌的影响

研究了筒体温度对微熔铸半固态熔体铝合金A356晶粒形貌的影响。结果表明, 在适当的温度范围内, 配合一定的搅拌速度, 能形成组织均匀、晶粒细小的A356半固态熔体。当筒体温度为620℃, 搅拌速度为800r·min-1时, 可制备出优质的A356半固态熔体, α-Al晶粒的平均尺寸为54μm, 形状因子为0.66, 熔体样品的显微硬度为HV 82.97。     

浇注温度对合金熔体冷却规律和半固态组织的影响

介绍了一种实验室自主研发的轻合金半固态浆料制备设备——锥桶式流变成形机(TBR),该设备利用刻有凸纹和沟槽的内、外锥桶的相对转动,使合金熔体在凝固过程中受到剧烈的剪切搅拌,从而获得合金半固态浆料.对TBR工艺的传热模型进行了推导,以A356为实验材料得出制备的A356铝合金半固态浆料温度与浇注温度的关系式,同时分析了不同浇注温度下合金熔体的冷却规律和获得的半固态组织形貌.结果表明,适当降低A356合金熔体的浇注温度可以延长初生固相受到的剪切时间和增加剪切次数,从而获得细小、均匀的半固态组织.当浇注温度为640℃时,初生固相平均晶粒尺寸为68μm,形状因子为0.82.     

Al-Mg-Si-Cu合金近液相线半连续铸造组织研究

采用近液相线半连续铸造方法制备了Al-1.2Mg-0.8Si-0.4Cu合金半同态锭坯,研究了浇注温度和铸造速度对锭坯微观组织的影响.合金熔体在750℃下浇注,组织不均匀,边部是细小的晶粒,1/2半径和中心部位是粗大的枝晶,最小晶粒直径25 μm,最大晶粒直径达220μm;660℃保温后浇注,可以获得适合半固态加工的均匀、细小的近球形组织,锭坯中心和边部组织差异小,平均品粒尺寸为36.5μm;铸造速度达150 mmm/min时有利于均匀、细小的近球形组织形成.结果表明,对于Al-1.2Mg-0.8Si-0.4Cu铝合金采用近液相线半连续铸造可以获得理想的半固态浆料.     

双螺旋流变压铸AZ91D镁合金的研究

液态压铸是镁合金最主要的成形方式,但液态压铸件存在气孔等缺陷,限制了镁合金的进一步推广使用。介绍了采用双螺旋流变制浆技术,对镁合金AZ91D进行了流变压铸研究。首先,将镁合金AZ91D熔体浇入到双螺旋流变制浆机中,然后根据不同工艺参数制备流变镁合金浆料,待制浆结束后,将半固态浆料转移到压铸机内,制得半固态压铸件。采用Micro-Image Analysis&Process(MIAP)软件分析了双螺旋流变制浆工艺参数(搅拌温度、搅拌时间和转速)对镁合金AZ91D的初生相晶粒大小的影响,并研究了镁合金压铸成形性。结果表明:随着搅拌温度的降低,晶粒尺寸变化不是很大;随着搅拌时间延长,镁合金晶粒尺寸逐渐增大;随着搅拌速度的增加,镁合金平均晶粒尺寸减少。镁合金流变压铸件中的初生α相由搅拌中形成的球状晶及压铸过程中二次凝固形成的更为细小的球状晶组成。对比了普通压铸件与流变压铸件热处理后的力学性能,流变压铸件的力学性能得到大幅提高,其原因归结为铸态组织的细小和均匀化。     

5083铝合金搅拌摩擦焊接头组织及力学性能研究

采用搅拌摩擦焊焊接5083铝合金,光学显微镜OM、透射电镜TEM对焊接接头进行金相分析,拉伸试验和硬度试验对焊接接头力学性能进行分析。结果表明,焊接接头焊核区为晶粒细小的等轴晶组织,热力影响区晶粒细小且沿剪切方向拉长,热影响区晶粒明显长大。其接头的力学性能显著优于传统的熔化焊,抗拉强度约为母材的90%,塑性与母材相当;硬度分布均匀,可达母材的90%。     

机械搅拌对中碳钢钢液凝固组织的影响

研究了中碳钢钢液在凝固初期施加机械搅拌,改变搅拌参数对钢液凝固组织的影响。实验结果表明,随着搅拌时间的延长等轴晶比例增大,搅拌时间30 s时,等轴晶比例最大为50.784%;改变插入钢液深度,随着插入液面深度的增加,等轴晶区比例明显增大,同时晶粒得到细化,分布更均匀,插入深度为4.5 cm时,等轴晶比例和晶粒细化程度达...     

温度与保温时间对半固态粉末轧制AA2024带材性能与显微组织的影响

采用半固态粉末轧制法制备2024铝合金带材,研究粉末加热温度和保温时间对轧制力、带材的相对密度及显微组织的影响。结果表明:2024铝合金带材的相对密度随粉末温度升高而增大,随保温时间延长而提高。粉末在585℃保温40 min后轧制,可获得形貌规整、无表观缺陷且晶粒细小均匀的等轴晶带材,带材相对密度达到93.28%。半固态粉末轧制力仅为室温下固态粉末轧制力的33.5%。半固态粉末轧制带材组织内仍存在少量孔隙,进一步热轧后可达到近全致密,显微硬度提高77.8%。因此,半固态粉末轧制对于缩短工艺流程,减小轧制力,制备高致密度的2024铝合金带材具有明显的优势。     

TiH_2/SiC粉末搅拌球磨及真空烧结制备超细晶钛

对TiH2/SiC混合粉末进行搅拌球磨,然后通过压制与真空烧结制备金属钛,研究球料比、球磨转速及球磨时间等工艺参数对球磨粉末粒度与显微组织的影响,并通过对烧结钛的组织观察与分析,研究此工艺制备超细晶钛的可行性。结果表明:适度提高转速或延长球磨时间有利于TiH2粉末的高效细化并提高粉末粒度分布的集中度;在球磨过程中没有发现TiH2分解和形成其他新相的现象;随球磨粉末的中位径D50和粒度跨度值ψ减小,烧结金属钛的晶粒度变得更小、更均匀。在600r/min转速下搅拌球磨8h后的TiH2/SiC粉末,在1050℃/3h条件下高真空烧结后得到平均晶粒度在5μm以下的超细晶钛。     

60Si2Mn弹簧钢半固态浆料的制备研究

研究了60Si2Mn弹簧钢半固态浆料的制备规律，结果表明：在本实验条件下，当搅拌时间为2min时，可以获得尺寸大小为100-300μm、固相率为40％～50％的球状初生奥氏体的半固态浆料，这样的半固态浆料便于从搅拌室底孔中放出；电磁搅拌使60Si2Mn弹簧钢熔体获得均匀的温度场和溶质场，抑制了发达的初生奥氏体枝晶的形成，为球状晶的获得奠定了基础；电磁搅拌引起蔷薇状初生奥氏体枝晶出现强烈的温度起伏和枝晶臂根部熔断是获得球状晶粒最重要的原因。     

Melt Conditioned Direct Chill (MC-DC) Casting of Al Alloys

A fine and uniform microstructure is always desirable for aluminium billets produced by direct-chill (DC) casting. Although this is usually achieved by grain refiner addition during DC casting, in this paper we demonstrate a physical approach for grain refining DC cast billets. Intensive melt shearing is applied to DC casting by submerging a rotor–stator based high shear device in the sump of a conventional DC caster. It has been shown that DC casting with intensive melt shearing can achieve one order of magnitude grain size reduction without using chemical grain refiners. Such fine and equiaxed grain structure in the Al billets can be attributed to enhanced heterogeneous nucleation and growth under conditions with reduced temperature gradient and increased growth velocity.     

Processing-structure characterization of rheocast IN-100 superalloy

The rheocasting solidification process has been applied in the production of IN-100 nickel base superalloy. A high vacuum furnace for rheocasting superalloys was used to rheocast ingots under different processing conditions. Processing variables which were evaluated include stirring speed, isothermal stirring time, and volume fraction solid during isothermal stirring. Ingots, furnace cooled at the same rate but without stirring, were also examined for comparison with the rheocast ingots. A detailed microstructural examination was made of the resultant microstructure both on furnace cooling after stirring and on reheating to the isothermal stirring temperature followed by water quenching. Rheocasting yielded fine-grained structures, where the extent of microsegregatiori, the variation in macrostructure, and the solidification-induced porosity were found to be reduced in comparison to the unstirred ingot. The grain size and nonuniformity in the as-cast ingot were reduced by increasing the stirring speed, isothermal stirring time, or the volume fraction solid during stirring. The degree of the microsegregation decreased significantly with increasing volume fraction solid. Grain boundaries, both with and without solute enrichment, were found in the rosette-like solid particles after rheocasting, lending support to the Vogel-Cantor-Doherty model of rheocasting based on the formation of grain boundaries by strain-induced recrystallization and by sintering. It is clear from these results that the microstructure of this superalloy was significantly improved by rheocasting. Improved mechanical properties were also found and will be reported separately.     

Semisolid Slurry Preparation of Die Steel with High Chromium Content

The semisolid slurry preparation of die steels Cr12 and Cr12MoV with high chromium content was studied. The results show that the semisolid slurry of both steels with solid of 40%-60% can be made by electromagnetic stirring method and is easy to be discharged from the bottom little hole of the stirring chamber. The sizes of the spherical primary austenite in the slurry of die steels Cr12 and Cr2MoV are 50-100 μm and 80-150μm, respectively. The homogeneous temperature field and solute field for both steel melts are obtained. The strong temperature fluctuation in the melt with many fine primary austenite grains occurs and the remelting of the secondary arm roots at the same time is accelerated because of the electromagnetic stirring. These are the most important reasons for deposition of spherical primary austenite grains.     

Study on Carburizing and Temperature Rising of the Semi-Steel Melt with Plasma Heating

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基于宾汉姆体的高浓度尾砂浆剪切变稀规律研究

高浓度尾砂浆的活化搅拌一直是矿山充填技术研究的重要方向,采用高速搅拌活化充填料浆是破坏充填料浆“团块”的有效办法,能够明显改善充填料浆的流变特性,提高其可输送性。高速搅拌过程的实质是对充填料浆进行快速剪切,不同的搅拌能对应不同的剪切速率,料浆的物化性质也相应地存在差异。为研究这种差异的规律并寻找高浓度尾砂浆的最佳活化能,针对某铜矿充填用尾砂,配制了浓度为70%的尾砂浆,采用新诺AM300S-H实验室搅拌机对尾矿浆开展了多种转速的搅拌实验,并采用Broofield R/S-CCT型流变仪分别测试其流变参数,通过Bingham模型分析了剪切变稀特性。研究结果表明：高浓度尾矿浆的黏度（ηb）和屈服应力（τ0）随搅拌速率（n）的增加而减小,表现出明显的剪切变稀特性,当转速达到400 r/min之后,尾砂浆的屈服应力不再明显减小,有趋于稳定的特性;在转速为120~1 000 r/min的范围内,其黏度与剪切转速之间的关系可用ηb=0.3n-0.1表示。     

氟盐法制备Al-Ti-B中间合金工艺优化

采用氟盐与过热铝反应,在不同的工艺条件下制取Al—Ti—B中间合金。从Ti、B的回收率、反应生成 物以及微观组织的角度,对盐的加入顺序、加入方式、作用时间、搅拌强度等因素做了定性分析,对一些出现的问题 分析了原因并提出了解决方案。结果表明,在制备Al—Ti—B中间合金过程中,K2TiF6与KBF4应当充分混合一并 加入铝液,并且采用铝箔包好分批加入,或平铺在坩埚底部将熔炼好的铝液冲入反应;反应过程中应根据不同工艺 合理控制反应时间,并尽量加强搅拌。本文还提出在定性分析的基础上对合金成分、反应温度、作用时间等重要因 素进行正交试验,并引入稀土元素制取Al—Ti—B—Re中间合金细化剂。     

Effects of process parameters on surface quality,composition segregation,microstructure and properties of QSn6.5-0.1 alloy slabs fabricated by HCCM horizontal continuous casting

Columnar-grained QSn6. 5-0. 1 alloy slabs with a width of 70 mm and thickness of 10 mm were fabricated by heating-cooling combined mold( HCCM) horizontal continuous casting. The effects of process parameters on solidification microstructure,surface quality,composition segregation and mechanical properties were studied. The results showed that the slabs with good surface quality,excellent mechanical properties and no obvious segregation could be prepared at the melt casting temperature of 1 250 ℃,the heating-mold temperature of 1 150- 1 200℃,the cooling water flow rate of 600 L / h and the casting speed of 20- 80 mm / min. The slabs had the yield strength of 124- 155 MPa,the elongation rate of 46. 6%- 56. 3% and the surface roughness of 0. 22- 0. 55μm,which enabled them to be directly processed without subsequent milling surface. The ratio of Sn content in the surface to that in the core was 0. 83- 1. 10,with an average value close to 1. 0,and not obviously influenced by process parameters. When the casting speed increased from 20 to 80 mm / min,the grain size changed little if the other process parameters were the same. When the heating-mold temperature increased from 1 150 to 1 200℃,the grain size was obviously refined and became more uniform if the casting speed was the same. Within the range of the casting speed at which the columnar grain structure could be obtained,the columnar grain size was mainly influenced by the heating-mold temperature.