半固态ZL101合金重熔加热时初生相的组织演变

利用低过热度浇注技术制备了半固态ZL101铝合金坯料,研究了半固态温度区间重熔加热时半固态ZL101铝合金坯料的初生相形貌的转变过程。研究结果表明,在半固态两相区保温,半固态ZL101合金的初生相逐渐团球化,该过程随保温温度的升高而加快。半固态ZL101铝合金晶粒的圆度与保温温度和保温时间的关系不大,但晶粒的尺寸随着保温温度和保温时间的增加而增大。半固态ZL101合金试样重熔加热最佳工艺制度为583℃下保温30m in,其晶粒平均等积圆直径为80μm,晶粒平均圆度为0.83。     

低过热度半连续铸造AlMg0.9Si0.6合金重熔工艺的研究

采用光学显微镜及图像分析软件,研究了A1Mg0.9Si0.6合金低过热度半连续铸造坯料在不同加热温度及保温时间下重熔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组织演变及晶粒长大过程.结果表明:重熔加热温度及保温时间共同影响着合金重熔组织的演变进程,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;有效控制AlMg0.9Si0.6合金重熔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浆料组织.     

AlSi7Mg合金低过热度半连续铸造组织的重熔演变

采用光学显微镜及图像分析仪,研究了AlSi7Mg合金低过热度半连续铸造坯料在不同加热温度及保温时间下重熔的微观形貌及尺寸特征,结合差热分析的方法研究了加热过程中组织演变及晶粒长大过程。结果表明,重熔加热温度及保温时间共同影响着合金重熔组织的演变进程,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。有效控制AlSi7Mg合金重熔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浆料组织。     

半固态2A12铝合金部分重熔组织的演变

对低压脉冲磁场技术制备的2A12铝合金半固态坯料进行部分重熔,利用光学显微镜和图像分析仪等,对半固态坯料部分重熔微观组织的演变进行了研究.结果表明,随着加热温度的提高或保温时间的延长,坯料的平均晶粒尺寸增大,重熔液相增加,晶粒的圆整度提高.最佳的部分重熔工艺参数如下:加热温度为620℃左右,保温时间为20～40 min.形成初生α-Al晶粒为均匀的近球形颗粒,平均晶粒尺寸为116～120 μm,液相率在40％左右,适合于半固态触变成形.组织演化机制分析表明,部分重熔的初期阶段,重熔液相较少,晶粒主要通过凝并快速长大;随加热温度的升高和保温时间的延长,重熔液相增加,晶粒主要通过原子扩散慢速长大并发生球化.     

挤压态7075铝合金半固态加热过程中的组织演变

研究了加热温度和保温时间对部分重熔再结晶方法(RAP)制备7075铝合金半固态坯料过程中的组织演变的影响。结果表明,通过在半固态温度区间加热可以将挤压态7075铝合金的纤维组织转变为半固态颗粒状晶粒组织。随着加热温度的提高和保温时间延长,挤压态组织逐渐消失,颗粒状晶粒经再结晶生长并合并长大;颗粒状晶粒的尺寸随加热温度和保温时间的增加而变大。在试验条件下,高温短时间加热比低温长时间下获得的半固态组织更加细小均匀。通过试验得出RAP法制备7075铝合金半固态坯料的优化工艺参数为600℃下保温5min。     

等径道角挤压AZ91D镁合金的半固态组织演变

通过半固态重熔实验,并利用金相显微镜,对等径道角挤压AZ91D镁合金的半固态组织演变进行了研究.结果表明:等径道角挤压后二次加热等温处理是一种适于AZ91D镁合金的制坯方法,加热温度对坯料的组织有很大影响.当保温时间一定时,随着加热温度的升高,先是球化效果越来越好,后来发生晶粒合并长大现象,晶粒尺寸也会逐渐长大,当保温时间为15 min,加热温度为560℃时,二次加热组织最好;当加热温度一定时,随着保温时间的延长,晶粒尺寸有长大的趋势,当加热温度为560℃,保温时间为15 min时组织球化效果最好,晶粒最细小;当加热温度和保温时间一定时,随着挤压次数的增加,二次加热组织的晶粒尺寸减小.     

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。     

Al-4Cu-Mg合金半固态重熔时的组织演变

文章研究了Al-4Cu-Mg合金半固态重熔过程中加热温度和保温时间对微观组织形貌和α晶粒尺寸的影响,并对组织演化机制进行了探讨。实验结果表明,当加热温度较低或保温时间较短时,晶粒尺寸小且均匀性差。由于液相分数少,α晶粒之间粘连严重。随着加热温度的升高或保温时间的延长,α晶粒发生了长大和圆整化。对于Al-4Cu-Mg合金来说,合适的半固态重熔参数为:加热温度为540℃~580℃;保温时间小于10min。在半固态重熔过程中,α晶粒的合并长大和Ostwald长大是其微观组织演化的主要机制,两种晶粒长大机制在重熔过程中所起的作用受液相体积分数的影响。     

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。     

原位内生TiB_2/Al-4Cu复合材料半固态二次加热组织演化

对原位内生TiB2/Al-4Cu复合材料半固态坯料进行二次加热,利用光学显微镜,图像分析仪等手段,对坯料二次加热微观组织的演化进行了研究。结果表明,随着加热温度的升高和保温时间的延长,液相分数增加,α(Al)晶粒发生了长大和圆整化。TiB2/Al-4Cu复合材料合适的半固态重熔参数为:加热温度570～600℃,保温时间小于10min。组织演化机制分析表明,二次加热初期,液相少,晶粒主要通过快速合并长大。随着加热温度的升高和保温时间的延长,液相增加,晶粒主要通过原子扩散缓慢长大并发生球化。     

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.     

脉冲电场下制备AZ91D镁合金部分重熔过程的组织演变

研究利用低压脉冲电场技术制备的AZ91D镁合金在部分重熔过程中的组织演变,考察加热温度和保温时间对不同脉冲电压制备的AZ91D合金初生相形态和尺寸的影响。结果表明:经低压脉冲电场处理后,将AZ91D镁合金进行部分重熔可得到非枝晶的半固态合金,随坯料制备的脉冲电压增加,重熔时初生相变得圆整且尺寸减小,但制备坯料的脉冲电压过高,重熔时初生相尺寸有所增加;脉冲电场处理后的AZ91D镁合金坯料经适当的部分重熔处理可获得具备触变过程所需要的组织状态。     

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.     

Microstructure evolution of semi-solid 2024 alloy during two-step reheating process

A two-step reheating process was proposed and applied to perform reheating experiments on the semi-solid 2024 alloy billet. In this process, the semi-solid billet was firstly heated over liquidus temperature and then isothermally held at solid-liquid zone temperature. Microstructure evolution of the semi-solid billet during two-step reheating was studied by optical microscope and compared with that during isothermal reheating. The results show that the remelting rate of the semi-solid billet during two-step reheating is faster than that during isothermal reheating. Under the same reheating time, the grains of the semi-solid billet reheated by two-step reheating process are finer and rounder than those by isothermal reheating process. The present experimental results indicate that accelerating the formation of liquid phase during the two-step reheating process can restrain the coalescence of grains to a certain extent, and thus refine the grain size and promote the grain spheroidization.     

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。     

SEMI-SOLID MICROSTRUCTURE AND ITS EVOLUTION OF WROUGHT ALUMINUM ALLOY BY DIRECTLY HEATING-ISOTHERMAL TREATMENT

Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the recrystallization microstructure was proposed. The results show that increase in reheating temperature and time can augment the volume fraction of liquid phase and accelerate the grain spheroidization, as a result of which the requirement of semi-solid forming can be satisfied. Due to the higher aberration energy of grain boundary, the melting point is lowered as a result of the easy diffusion of atoms. At higher reheating temperature the grain boundary melts, the growth of the recrystallized grain is inhibited and the grain is refined. The composition of the low melt-point phase along the recrystallized grains was determined using EDS. It can be seen from the experimental results that when the extrusion rod of the wrought aluminum alloy is reheated at 610℃ for 20min, perfect fine equiaxial grains can be obtained, the average grain size is about 66.34μm and the volume fraction of solid phase is about 68%.     

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.     

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。