等温处理对挤压态AZ80A镁合金半固态组织的影响

采用应变诱发熔化激活法(SIMA)工艺制备了AZ80A镁合金半固态坯料,研究了保温温度和保温时间对半固态组织的影响。结果表明:随着保温温度的升高和保温时间的增加,AZ80A镁合金的平均晶粒尺寸与液相率都呈上升趋势,形状因子呈先增大后减小的趋势。半固态组织由α-Mg晶粒、Al、Zn元素富集形成的晶界处液相和晶内“小液池”组成,其组织演变分为初始晶粒合并长大,晶粒球化、彼此分离,最终合并粗化3个阶段。采用该种方法制备AZ80A镁合金半固态坯料时合适的保温温度为550 ℃、保温时间为45 min,此时半固态组织的平均晶粒尺寸、形状因子和液相率分别为89 μm、0.795和26.7%。     

Effect of La addition on semi-solid microstructure evolution of Mg-7Zn magnesium alloy

Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment. The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated. Meanwhile, the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied. Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure. During the semi-solid thermal transformation, the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time. The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605 °C for 30 min is the optimal. The average size of solid particles, shape factor, and solid fraction are 42 µm, 1.45 and 61.8%, respectively. At the same time, a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.

     

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

By means of equal channel angular extrusion (ECAE) test, upsetting test and metalloseope, reheating mierostruetures 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 microstrueture 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 microstrueture 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.     

Microstructure evolution of semi-solid SiCp/AZ91D nanocomposite during isothermal heat treatment process

ABSTRACT

The microstructure evolution of semi-solid SiC_p/AZ91D nanocomposite during isothermal heat treatment process in the mushy-zone was investigated. The results indicate that the nano-size SiC particles in composite are distributed uniformly and the grains are refined significantly by the addition of nano-size SiC particles. The semi-solid microstructure evolution experiences four stages during isothermal heat treatment process: the initial coarsening, structural separation, spheroidization and final coarsening. The grain size of the primary α-Mg phase decreases with the increasing of holding temperature. With the prolongation of holding time, the grain size of the primary α-Mg phase decreases at first and then increases. The optimum isothermal heat treatment parameter is 575℃ for 30min, under which the average grain diameter is 58μm and shape factor is 1.25.     

AZ61合金半固态二次加热工艺及组织演变

研究了应力诱发熔体激活法(SIMA)制备的AZ61镁合金半固态坯料在二次加热时加热温度和保温时间对其组织的影响,研究表明,二次加热初期半固态组织首先熔合合并,随着保温时间延长,晶粒逐渐长大和球化,液相份数增加;保温温度越高,晶粒长大和球化速度加快。在592℃加热、保温20min~40min,可以获得均匀、圆整的半固态组织,晶粒大小为80μm~90μm,液相率为40%~42%。高于597℃时,试样重熔过程中易发生严重变形。     

半固态T12钢局部重熔组织的演变

对半固态高碳工具钢T12坯料在不同温度、不同保温时间下局部重熔后的组织演变进行了研究。结果表明,半固态T12钢坯料具有非枝晶和近球形的显微结构。半固态坯料局部重熔时,随着温度的升高和保温时间的延长,晶粒尺寸和圆整度都有所提高;局部重熔温度越高,保温时间越长,形状因子值越大、越接近1。     

6061铝合金半固态坯料二次加热工艺及组织演变

针对近液相线半连续铸造技术制备的6061铝合金半固态坯料,在不同加热温度及保温时间下进行二次加热,采用光学显微镜及图像分析仪考察试样的微观形貌及尺寸特征,结合差热分析的方法研究加热过程中的液相形成、组织演变及晶粒长大过程。结果表明,二次加热温度及保温时间共同影响着微观组织演变过程,随着加热温度升高及保温时间延长,晶粒逐渐球化并长大。加热温度越高,组织演变速度越快;保温时间越长,晶粒球化并长大越明显。有效地控制二次加热温度及保温时间,能够获得均匀、圆整且相对细小的半固态组织。     

冷变形对LC9铝合金等温转变半固态组织的影响

对冷变形金属进行等温加热转变制备半固态LC9铝合金坯料，并对其工艺过程及组织演变进行了研究，讨论了变形量、加热温度和保温时间等工艺参数对LC9铝合金组织的影响。结果表明，对冷变形金属采用等温处理，可获得均匀、细小的半固态坯料，很好地满足半固态制坯的要求；增加变形量使组织中的液相比例明显增加，晶粒尺寸变小；提高加热温度或延长保温时间有利于晶粒粒化，但是过高的温度和保温时间，会加快晶粒长大，促使晶粒粗化。     

A356铝合金半固态成形坯料二次加热工艺的优化

使用多工位电磁感应旋转加热装置对A356圆棒料进行重熔加热。选用不同的加热功率和工位,得到不同的非树枝晶组织,借助晶粒参数(如晶粒平均大小、形状系数、固相率等)对得到的显微组织进行研究,选出综合指标最优的加热工艺,再对该工艺加热的坯料压铸成阶梯试样。通过对阶梯试样性能分析,验证了该工艺的合理性和优越性。结合凝固理论,分析了坯料二次加热的演变规律。     

Effects of processing parameters on microstructure of semi-solid magnesium alloy

In this paper, the effects of pouring temperature of magnesium melt, preheating temperature of the barrel of the screw mixer, and shear rate on the solidified microstructures of semi-solid slurry were investigated by a mechanical stirring semi-solid process. The appropriate processing parameters of slurry preparation were obtained, and the mold filling ability of semi-solid slurry for thin-walled casting was examined. Results indicate that the solid volume fraction of non-dendritic microstructure increases with a decrease in pouring temperature of magnesium melt and the barrel preheating temperature of the screw mixer. Also the grain size of primary α-phase is reduced. Furthermore, the solid volume fraction of semi-solid nondendritic structure decreases with an increase of shear rate. The fine and round granular microstructure with 30～50 μm in size of semi-solid AZ91D magnesium alloy was presented. Finally, a 1.0 mm thin-walled casting with a clear contour and good soundness was successfully made by semi-solid rheo-diecasting.     

Taper barrel rheomoulding process for semi-solid slurry preparation and microstructure evolution of A356 aluminum alloy

The self-developed taper barrel rheomoulding (TBR) machine for light alloy semi-solid slurry preparation was introduced. The semi-solid slurry was obtained from the intense shearing turbulence of the alloy melt in the cause of solidification, which was further caused by the relative rotation of the internal and external taper barrel whose surface contained wale and groove. The heat transmission model of TBR process, the flow rules and the shearing model of the alloy melt were deduced. Taking A365 as experimental material, the microstructure evolution rules under different slurry preparation processes were analyzed. The results show that decreasing the pouring temperature of A365 alloy melt properly or increasing the shearing rate helps to obtain ideal semi-solid microstructure with the primary particle size of about 70 μm and the shape factor of above 0.8.     

等温温度对轧制SIMA法制备7075合金半固态显微组织的影响

分别采用以同步轧制和异步轧制为预变形方式的应变熔化激活法(SIMA)制备7075铝合金半固态坯料,研究了辊径比和等温保温温度对预变形板材热处理过程中组织演变的影响。结果表明:随等温温度的升高,初生固相晶粒内生成大量液相,固相晶间冷却后出现大量共晶相。在相同的热处理条件下,异步轧制预变形工艺能够比同步轧制预变形工艺获得更多液相,且半固态进程更迅速;获得半固态坯料的优化工艺条件为异步轧制作预变形、等温温度选择610 ℃。     

Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy

The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.     

7A04合金半固态触变模锻的组织演化

研究了SIMA法制备的7A04合金在半固态触变模锻工艺中的组织演化规律.结果表明:在半固态重熔加热过程中,随着加热温度的升高和保温时间的延长,晶粒逐渐球化和长大,且加热温度对重熔加热组织的影响比保温时间大;当将具有此特征的坯料进行半固态触变模锻后,其获得的触变模锻件的显微组织与半固态重熔组织密切相关.当模锻温度达到600℃以上时,模锻件的显微组织变化不大,仍是均匀的近球形的显微组织,而且模锻件各区域的合金成分基本一致.揭示了采用半固态触变模锻工艺可获得形状复杂的高质量制件.     

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 120min, ZA84 magnesium alloy can obtain a non-dendritic microstructure with 14.2%-25.6% liquid fraction and an average size of 56-65μm of the unmelted primary solid particles. With the increasing holding time from 30 to 120min 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. structulseparation and spheroidization. The subsequent coarsening of spheroidal grains is not observed.     

Effect of original microstructures on microstructural evolution of A2017 semi-solid alloy billets during reheating

The microstructural evolution of the A2017 semi-solid alloy billets provided with rheocasting and extruding/extending forming by shearing-cooling-rolling(SCR) technology during reheating in semi-solid state was investigated. The microstructural differences and their generation causes for both billets were also analyzed. The results show that during reheating, the grains of rheocasting billets grow up and spheroidize gradually with the prolongation of isothermal holding time, the eutectic liquid phase at low melting point forms mainly among the grains. However, the grains of the extruding/extending forming billets grow up abnormally through grain coalescence in the initial stage of the reheating, the entrapment of large amount of liquid within grains occurs, and the grain sizes in the reheating billets are coarse and inhomogeneous. Compared with extruding/extending forming billets, rheocasting billets have smaller and uniform grains in reheating microstructure and can rapidly form liquid phase among grains. Therefore, rheocasting billets are more suitable for the semi-solid forming than the extruding/extending forming billets.     

Effect of heat treatment on microstructure and properties of semi-solid squeeze casting AZ91D

Semi-solid AZ91D magnesium alloy billets were prepared by near-liquidus heat holding. Semi-solid squeeze casting was conducted at 575, 585 and 595 ℃, respectively, with 1 mm·s~(-1) squeeze speed. The semisolid squeeze casting AZ91D samples were heat treated by T4(solution at 415 ℃ for 24 h) and T6(solution at 415 ℃ for 24 h + 220 ℃ for 8 h) processes, respectively. The microstructure and mechanical properties of the alloy in different states were investigated by means of OM, SEM and tensile testing machine. The results show that compared to as-cast alloy, the grain size of the semi-solid squeezed AZ91D decreased significantly, and with the increase of semi-solid squeeze temperature, the grain size of AZ91D increased. The grains of the alloy were refined by T4 treatment, and further refined by T6 treatment. T6 treatment greatly improved the tensile strength, elongation, and hardness, but did not significantly improve yield strength. After 575 ℃ squeeze casting and T6 treatment, the ultimate tensile strength(UTS) reached 285 MPa, the elongation reached 13.36%, and the hardness also reached the maximum(106.8 HV), but the yield strength(YS) was only 180 MPa. During the process of semi-solid squeeze casting and heat treatment, the matrix grain was refined and a large number of precipitated and secondary precipitated phases of Mg_(17)Al_(12) appeared. Both the average size of matrix grain and secondary precipitated phase decreased, while the volume fraction of secondary precipitated phase increased. All these resulted in high tensile strength, elongation and hardness.     

蛇形通道浇注制备半固态7075铝合金浆料(英文)

采用蛇形通道浇注技术制备半固态7075铝合金浆料,研究浇注温度和弯道数量对半固态7075铝合金浆料微观组织的影响。结果表明:当浇注温度为680~700°C时,可以制备出质量较好的半固态7075铝合金浆料;在相同浇注温度条件下,随着弯道数量的增加,初生α(Al)的平均晶粒尺寸减小,形状因子提高。在浇注制备半固态7075铝合金浆料过程中,合金熔体在具有一定弧度且封闭的蛇形弯道内流动并多次改变流动方向,具有类似"搅拌"的功能,使得初生晶核逐渐演变为球形或近球形晶粒。     

Effect of Semi-Solid Isothermal Heat Treatment on Microstructure of ZL104 Aluminum Alloy

The feasibility of fabricating ZL104 aluminum alloy with non-dendritic microstructure by 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, are investigated. The research results indicate that it is possible to produce ZL104 alloy with non-dendritic microstructure by a suitable semi-solid isothermal heat treatment. After treated at 580 ℃ for 120 min, the ZL104 alloy can obtain a non-dendritic mic...     

机械振动法制备铝合金半固态浆料的研究

研究了利用机械振动法制备铝合金半固态浆料的新工艺。首先进行水模拟实验，研究机械振动条件下容器中液体的对流运动情况，然后进行振动制备ZL101铝合金半固态浆料实验，获得了初生晶粒细小、圆整度好的半固态浆料。实验选取振动频率（振幅）和保温时间两个参数，研究了它们对晶粒形状系数以及晶粒尺寸的影响规律。结果发现，初生晶粒的形状系数随着保温时间的延长，先是有所增大，然后由于晶粒的合并长大而下降；振动的振幅越大，晶粒越圆整，形状系数越大。初生晶粒的尺寸随着振幅的增大而减小，随着保温时间的延长而增大。