流变铸造半固态亚共晶高铬铸铁组织形成研究

研究了亚共晶高铬铸铁半固态球状晶的形成条件及规律。结果表明：通过控制合适的浇注温度，并对充型前的金属液进行激冷处理，同时对过冷的金属液配以适当的振动，可以获得球形或近球形的先共晶奥氏体非枝品组织；在带有倾斜板冷却体的低温浇注情况下，金属液的冲刷、流动及振动使熔体获得了均匀的溶质场和温度场，抑制了发达的先共晶奥氏体枝晶的形成，为球状晶的获得提供了条件。     

倾斜板角度对亚共晶高铬铸铁半固态组织的影响

采用倾斜板冷却体法对亚共晶高铬铸铁进行半固态成形,研究倾斜板角度对亚共晶高铬铸铁半固态组织的影响规律,并借助Imagetool图像分析软件分别定量分析了其初生奥氏体的形状系数和等效直径的变化特征.结果表明改变倾斜板角度可明显改善亚共晶高铬铸铁初生奥氏体的形貌,为球状晶的获得提供了条件.     

倾斜板角度对亚共晶高铬铸铁半固态组织的影响

采用倾斜板冷却体法对亚共晶高铬铸铁进行半固态成形,研究了倾斜板角度对亚共晶高铬铸铁半固态组织的影响规律。结果表明:倾斜板角度过大或过小都将使得组织中的初生奥氏体较粗大、圆整度较小。当倾斜板角度较小时,金属液的流速相对较慢,枝晶与枝晶和枝晶与金属液间的冲刷、碰撞、剪切作用较小,晶粒易于长大,导致枝晶状初生奥氏体比较多。当倾斜板角度较大时,金属液流速相对较快,金属液在倾斜板上流动的时间相对较短,枝晶间以及枝晶与金属液间的冲刷、碰撞、剪切作用时间相对较短,导致枝晶状初生奥氏体也比较多。当倾斜板角度为45°时,制备的亚共晶高铬铸铁初生奥氏体的尺寸最小,圆整度最高。     

过共晶高铬铸铁半固态浆料制备及组织

采用倾斜板冷却体法制备了过共晶高铬铸铁半固态浆料,观察研究了制备试样的组织.结果表明:采用倾斜板冷却体法对过共晶高铬铸铁进行半固态成形,通过控制合适的浇注温度,同时对过冷的金属液加以适当的振动,可以细化初生碳化物,且使初生碳化物分布更加均匀,获得理想的过共晶高铬铸铁半固态组织.     

浇注温度对半固态亚共晶高铬铸铁初生奥氏体的影响

利用倾斜板冷却体法制备了亚共晶高铬铸铁半固态浆料,并且研究了不同浇注温度对半固态亚共晶高铬铸铁初生奥氏体的影响。结果表明,浇注温度低时,合金熔液获得的过冷大,初生奥氏体大量形核,颗粒细小、圆整;随着浇注温度的升高,合金获得的过冷减小,初生奥氏体形核率降低,液相原子扩散能力提高,长大机率增加,初生奥氏体明显长大,且朝枝晶状生长,颗粒尺寸变大、圆整度差、枝晶发达;当浇注温度进一步升高时,液相原子扩散能力再次加强,使得初生奥氏体周围液相的溶质浓度均匀,颗粒生长没有明显的方向性,初生奥氏体颗粒粗大、圆整。     

不同倾斜板凹槽半径条件下的亚共晶高铬铸铁组织

采用自制的倾斜板制备了亚共晶高铬铸铁半固态浆料,通过观察倾斜板凹槽半径为100 mm和400 mm两种条件下形成的先共晶奥氏体的形貌,就倾斜板凹槽半径对先共晶奥氏体的影响进行了初步探讨.结果表明,凹槽半径为400 mm与凹槽半径为100 mm时相比,先共晶奥氏体颗粒的平均形状系数增加,圆整度明显提高,平均等效直径减小,固相率略有增加,获得了具有非枝晶奥氏体的亚共晶高铬铸铁.     

机械振动对倾斜冷却板法制备亚共晶铝合金半固态组织的影响

采用自制的振动倾斜冷却板装置,研究了机械振动对A356铝合金半固态组织的影响.结果表明,与倾斜冷却板上不施加振动相比,施加振动获得的组织中初生α-Al相的非枝晶球状或粒状更多,更均匀、细小,且获得该组织的最佳浇注温度范围更宽.与逆向施加振动相比,顺向振动所获得的非枝晶组织中包含有较多的蔷薇状晶体,而且球状或粒状晶体较粗大,不均匀.振动形成大量游离等轴晶,以及振动对流所引起的晶粒运动导致晶粒在各个方向逆向均匀生长是A356铝合金半固态非枝晶组织形成的主要原因.     

半固态高铬铸铁组织形成研究

研究了高铬铸铁Cr20Mo2半固态浆料的组织形成规律.结果表明当搅拌时间为5～6 min时,可以获得尺寸大小为50～80 μm、固相率为40%～50%的球状先共晶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;电磁搅拌使高铬铸铁Cr20Mo2熔体获得均匀的温度场和溶质场,拟制了发达的先共晶奥氏体枝晶的形成,为球状晶的获得奠定了基础;电磁搅拌引起细小先共晶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.     

半固态高铬铸铁球状先共晶奥氏体的形成

采用自行研制的倾斜取样板进行取样,并借助金相图像分析系统研究了半固态高铬铸铁先共晶奥氏体的衍变过程。结果表明,金属液在流动过程中被倾斜板过冷,奥氏体不断形核长大成枝晶状,枝晶又由于相互间的碰撞、摩擦等物理作用被熔断、折断、破碎而得到细化、球化。上述过程交替出现,初期以奥氏体形核长大为主,后期以枝晶奥氏体被熔断、折断、破碎而被细化、球化为主。     

剪切/振动耦合作用下连续流变轧制成形A2017合金组织演化及动态凝固(英文)

将振动倾斜板制浆技术与轧制技术有机结合,开发新型连续流变轧制成形技术,利用该技术制备A2017合金板材。研究连续流变轧制成形过程中A2017合金组织演化及动态凝固行为。结果表明,在振动倾斜板制浆过程中,由于倾斜板的强冷却及振动作用,熔体内部形核率较高,晶粒有两种长大方式:一是直接球形长大,二是先枝晶生长然后断裂球化,因此促进了球形晶和玫瑰晶的形成。在半固态浆料轧制过程中晶粒被拉长。随着浇注温度升高,晶粒尺寸逐渐变大。当浇注温度为650660°C时,可以制备表面形貌和内部组织较好的A2017合金板材,其内部组织主要由球形晶和玫瑰晶组成。     

半固态灰铸铁的制备与显微组织

建立了一种不需搅拌和其它附加处理的半固态灰铸铁制备技术 ,用浇注前合理调整熔体温度或调温 适当快冷的铸造方法 ,并配以合适的凝固冷却速度 ,成功地制备了球状初生奥氏体圆整、尺寸细小、分布均匀的半固态亚共晶灰铸铁 ,得到了最佳工艺条件 ,并用铸铁金相计算机辅助检测系统 ,对初生奥氏体的形状系数和等效直径进行了测量与统计分析 ,定量描述了半固态组织的特性     

铸铁件消失模铸造对铁液温度的要求

介绍了采用消失模工艺铸造铸铁件提高浇注温度的原因,其中球铁浇注温度范围为:1380～1480℃,灰铸铁为1360～1420℃,合金铸铁(Cr系白口铁)为1380～1450℃;认为浇注温度过高容易引起粘砂、反喷、气孔等缺陷,浇注温度过低则易引起皱皮、冷隔等缺陷;提出了用消失模工艺生产灰铸铁、球墨铸铁、Cr系白口铸铁对铁液的调整要求。     

防止汽车支架类球铁铸件皮下气孔的产生

在浇注汽车支架类球铁铸件时,通过采取增设过滤网、集渣包; 提高浇注温度及速度; 分散内浇道、减少铁液与铸型的作用时间等措施,有效地减少了皮下气孔。     

Preparation of in situ-formed WC/Fe composite on gray cast iron substrate by a centrifugal casting process

An iron-based composite reinforced by in situ-formed tungsten carbide particles was fabricated on gray cast iron substrate by a centrifugal casting process. The as-prepared composite was characterized by X-ray diffraction, scanning electron microscopy, and microhardness and wear testers. An appropriate pouring temperature (1300 °C) of the gray cast iron melt was chosen considering the dissolution temperature of the tungsten wires determined by differential scanning calorimetry. The experimental results showed that the tungsten wires were dissolved partially by the cast iron melt. As a result, primary and secondary tungsten carbide particles and pearlite with a negligible amount of graphite flakes were formed as the reinforcing phase and the matrix, respectively. The composite with a thickness of about 3 mm was dense and metallurgically bonded to the gray cast iron substrate. Wear resistance was determined by a pin-on-disc wear test technique, indicating that the composite containing high volume fraction of hard tungsten carbides presented higher wear resistance compared with the unreinforced gray cast iron.     

半激冷灰铸铁凸轮轴表面缩陷的防止措施

采用覆膜树脂砂壳型、铁液从一端进入型腔的侧浇工艺,生产一种半激冷4100型Cr-Ni-Mo灰铸铁凸轮轴。讨论了铁液白口宽度、w（C）量、浇注温度对收缩缺陷的影响,将铁液w（C）量控制在3.65%-3.7%,CE控制在4.25%-4.38%,适当降低铁液浇注前的白口宽度,以及控制浇注温度在1 400-1 420℃,可以避免4100凸轮轴产生收缩缺陷。     

制动鼓铸造工艺性分析

分析了制动鼓产品的材料成分、性能等技术要求及失效机理,比较分析了顶注式、底注式、中间注入式等铸造工艺方法的优缺点及在实际生产中的应用,同时提出利用球墨铸铁材料取代灰铸铁材料生产制动鼓可提高产品的综合性能并大幅度节约能源。     

Fabrication of SiC particle dispersed spheroidal graphite cast iron composite by vacuum assisted casting and its microstructure

Abstract

SiC particle preforms were infiltrated with spheroidal graphite cast iron melt by vacuum assisted casting in the sand mould, and spheroidal graphite cast iron composites in which the particles were dispersed in the surface region were fabricated. Although the melt infiltration was not accomplished when the melt was poured under atmospheric pressure, the infiltration was accomplished by the vacuum assisted casting when the SiC particle volume fraction and preform thickness were optimised. When the Si content of the cast iron was 2˙5 mass%, the phase consisting of mainly Fe₃Si was formed at the particle/matrix interface due to the reaction between the cast iron melt and the particles during the infiltration. The matrix of the composite consisted of fine spheroidal graphite particles, ferrite, pearite and chill crystal. Although the increase in the Si content suppressed the reaction and chill, no infiltrated area was observed in the composite.     

Study on in-situ WC particles/tungsten wire reinforced iron matrix composites under electromagnetic field

By applying electromagnetic field to a system consisting of tungsten wires and grey cast iron melt, the grey cast iron matrix composite reinforced by either in-situ WC particles or the combination of in-situ WC particles and the residual tungsten wire was obtained. By means of differential thermal analysis (DTA), the pouring temperature of iron melt was determined at 1,573 K. The microstructures of the composites were analyzed by using of X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with an energy dispersive spectrum (EDS) and pin-on-disc abrasive wear test. The obtained results indicated that, with the enhancing frequency of electromagnetic field, the amount of in-situ WC particles gradually increases, leading to continuous decrease of the residual tungsten wires. When the electromagnetic field frequency was up to 4 kHz, tungsten wires reacted completely with carbon atoms in grey cast iron melt, forming WC particals. The electromagnetic field appeared to accelerate the elemental diffusion in the melt, to help relatively quick formation of a series of small Fe- W-C ternary zones and to improve the kinetic condition of in-situ WC fabrication. As compared with the composite prepared without the electromagnetic field, the composite fabricated at 4 kHz presented good wear resistance.