Effect of Temperature on Segregation and Deformation Mechanism of α+Ti2Cu Alloy during Semi-Solid Forging

以新型阻燃钛合金Ti14 (α＋Ti2Cu)为对象,研究了合金在不同温度半固态锻造过程中的偏析和偏聚现象及由此导致的变形机制的变化。结果表明,半固态温度影响液相含量和分布,随着温度的升高液相在晶界由不连续分布转变为连续分布析出,并最终形成了网状结构分布。锻造过程中由于液相和应力的共同作用出现了宏观偏析现象,液相在压力作用下的流动在晶界处产生了宏观液相/固相分离现象,靠近试样中心固相离子集中;这种现象导致了锻造过程中变形机制的变化,中心区仍旧是固相粒子的塑性变形为主变形机制,靠近试样外边缘主变形机制转变为固相粒子的相对滑移,通过唯象模型对其过程进行讨论     

半固态等温处理Mg-Zn-Y合金微观组织演变

研究了挤压Mg-2Zn-x Y(x=0.5,1,2,at%)合金在半固态等温处理过程中的微观组织演变规律。结果表明:3种Mg-2Zn-x Y合金中,挤压Mg-2Zn-1Y合金中α-Mg基体晶粒尺寸最小,挤压Mg-2Zn-2Y合金中出现了大量的孪晶;当半固态等温时间为10 min时,随着等温温度的升高,Mg-2Zn-x Y合金中α-Mg固相晶粒均逐渐趋于球化,且α-Mg固相颗粒逐渐分离,晶界处的液相和晶内液池体积分数均明显增加;随着580℃等温时间的延长(≤30 min),Mg-2Zn-0.5Y合金微观组织演变以Ostwald熟化机制为主,而Mg-2Zn-1Y和Mg-2Zn-2Y合金微观组织演变过程中Ostwald熟化机制和固相颗粒熔化机制同时起主导作用。     

Evolution and distribution of Al2Sm phase in as-extruded AZ61–xSm magnesium alloys during semi-solid isothermal heat-treatment

The evolution and distribution of Al₂Sm phase in as-extruded AZ61–xSm (x=0, 1.5, 2.0 and 2.5, mass fraction, %) magnesium alloys during semi-solid isothermal heat treatment were investigated. The results showed that when as-extruded AZ61 magnesium alloys were modified with Sm, the smaller and rounder grains were obtained during semi-solid isothermal heat treatment. When the Sm content is 2.0% (mass fraction), the average size of the globular grains reached the smallest value of 90 μm. Although a few Al₂Sm particles existed in the α-Mg grains, most of Al₂Sm particles solidified at the edge of the globular grains with the width of ~20 μm. These phenomena are mainly attributed to the forces acting on Al₂Sm particles in front of the solid–liquid interface, leading to Al₂Sm particles accumulating at the solid–liquid interface and then solidifying at the edge of the globular grains in the quenching process.     

Influence of semi-solid isothermal treatment on eutectic carbide in Cr12MoV steel

In-situ observation of eutectic solidification of Cr12MoV steel was conducted using high temperature confocal laser-scanning microscopy. The semi-solid isothermal treatment temperature of the steel was determined by thermodynamic calculation using Thermo-cal software. At the same time, the influences of isothermal treatment temperature and time on eutectic carbides in the steel were also studied. The results show that when the liquid metal cools at the rate of 47 ℃·min^-1, the eutectic reaction occurs rapidly at 1,214.7 ℃ in one second with the reticular liquid around austenite dendrites, transforming into a network of eutectic structure. After being held at 1,300 ℃ for 30 min, the carbide network is broken due to the impingement of refined primary austenite dendrites and secondary dendrites arms, and the thickness of eutectic structure is reduced.     

铝合金半固态浆料制备工艺参数的研究

通过研究半固态等温搅拌,探讨了不同的搅拌电流和搅拌频率对半固态浆料组织的影响,分析了枝晶断裂程度和断裂部分晶粒尺寸的变化规律,得到了合理的搅拌参数.通过试样金相对比,结果表明,与未经电磁搅拌的半固态浆料相比,经电磁搅拌的浆料初生晶粒更细小、圆整及均匀.电磁搅拌制备的浆料压铸所得的试样力学性能明显优于普通液态压铸试样的力学性能.     

Microstructure Study on Semi-solid 60Si2Mn during Compressing

The microstructure behavior and deformation mechanism of semi-solid 60Si2Mn fabricated by electromagnetic stirring under different deformation conditions during thixoforming are studied by means of Gleeble-1500 thermal-strain-stress simulator. The micro- structure of deformed 60Si2Mn and that of the non-deformed are compared. The results show that the grain size within deformation zone decreases as the amount of deformation increases or deformation temperature decreases, but deformation fate has small effect on grain size when the rate is very low. Besides, there is a critical amount of deformation to reduce grain size. These results offer theoretical and experimental basis for further producing semi-solid material with high melting temperature and direct forming of semi-solid slurry.     

Semi-solid squeeze casting of ignition-proof mg-ca-zr system alloys

The production method of the near-net shape molded Mg-Ca-Zr alloys by the devised semi-solid squeeze casting was established and the fabrication factors for sound products were also investigated. The Mg-Ca-Zr alloys having an ignition-proof property and very fine spherical structure provide high production safety and good fluidity for quality near-net shape products in semi-solid state processing. The orifice with a diameter of 30 mm and a plunger speed of 80 mm/s contribute successfully to infiltrate the semi-solid state prema-terial into the designed mold perfectly within the limited infiltration time. The tensile strengths and elongations of the ignition-proof Mg-Ca-Zr and Mg-Zn-Ca-Zr alloys are improved by applying the high pressure of 100 MPa, indicating that pressure more than 100 MPa is also an important fabrication factor.     

ZL201铝合金的触变锻造组织与性能

利用自行设计的模具,采用半固态触变锻造的方法,研究近液相线铸造法制备的ZL201铝合金半固态坯料触变成形件的组织和性能.结果表明,半固态闭模锻造成形后的成形件组织均匀、致密.合金在525℃～530℃固溶12h、155℃时效20h后,强化相充分溶解,均匀析出,合金的维氏硬度可达129.8HV.半固态触变锻造可以获得理想的成形件.     

Ti14合金半固态塑性变形的热力模拟

利用Gleeble1500热/力模拟机研究了Ti14合金在应变速率为5×10-3～5 s-1,变形温度为1273～1423 K,变形量为60%条件下的半固态塑性变形行为。分析了合金流变应力与应变速率、变形温度之间的关系,根据分析结果建立了Ti14合金半固态变形流变本构方程,结果表明:合金在半固态条件下存在明显的屈服现象,流变应力受温度和应变速率影响较大,稳态流变应力和峰值流变应力随温度的增加而减小,相同温度下,流变应力随应变速率的增加而增加,分析可能是由于液相含量和分布对初生α-Ti骨架的解聚作用所致。     

超声振动对半固态AZ61镁合金微观组织的影响研究

利用自行设计和研制的一套超声振动装置,试验研究超声导入温度、超声输出功率和超声处理时间对半固态AZ61镁合金微观组织的影响。试验结果表明,在半固态区间,只有将AZ61镁合金熔体控制在合适的温度时,才能获得细小、均匀的半固态球状组织;当超声振动时间为60 s时,对半固态AZ61镁合金超声处理的效果最好;随着超声振动功率的增加,熔体中的颗粒直径呈不断下降的趋势,晶粒尺寸得到的明显细化,形状趋于圆整。