加热工艺对AZ91D镁合金部分重熔组织的影响

提出半固态金属坯料先在液相线以上温度适当加热再降低温度至两相区温度继续等温保温的二次加热工艺。采用该工艺对晶粒细化AZ91D镁合金坯料进行部分重熔,研究了其组织演变规律,并与等温二次加热工艺进行比较。结果表明,与等温二次加热工艺相比,坯料先在液相线以上温度适当加热再降低温度至两相区温度继续保温,坯料重熔速度明显加快,相同加热时间时,晶粒更加细小和圆整。组织演变机理分析表明,加快液相形成速度可适当抑制晶粒的合并,降低晶粒长大速度,并促进晶粒球化。     

半固态2024合金部分重熔新工艺与组织演变

提出半固态坯料先在液相线以上某温度适当等温加热,然后再降低温度至两相区继续等温保温的两步法部分重熔新工艺.采用该工艺对低过热度浇注半固态2024合金坯料进行部分重熔试验,利用光学显微镜和金相图像分析系统,研究了坯料组织演变规律,并与两相区等温部分重熔工艺进行了比较.结果表明,采用两步法部分重熔工艺.由于坯料升温速度加快和熔化过热温度提高,抑制了晶间共晶相的溶解扩散,晶间液相形成速度明显加快,对晶粒合并长大具有一定的抑制作用,并加速晶粒球化,坯料部分重熔后,晶粒更加细小和圆整.     

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.     

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.     

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。     

半固态铝合金重熔组织演变的研究

通过自行研制开发的新型半固态连续机械搅拌设备,制备了半固态铝合金,并对半固态坯料在半固态温度区间重熔加热,研究不同重熔温度、时间下半固态组织的变化规律.研究表明:保温温度越高,晶粒长大和球化速度加快,保温时间越短;随着保温时间延长,晶粒逐渐长大和球化,液相份数增加.半固态铝合金Y112重熔加热适宜温度区间为565～575℃.     

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。     

Preparation of semi-solid billet of magnesium alloy and its thixoforming

Preparation of semi-solid billet of magnesium alloy and thixoforming was investigated by applying equal channel angularextrusion to magnesium alloy.The results show that mechanical properties of AZ91D alloy at room temperature,such as yieldstrength(YS),ultimate tensile strength(UTS)and elongation,are enhanced greatly by four-pass equal channel angularextrusion(ECAE)at 573 K and microstructure of AZ91D alloy is refined to the average grain size of 20μm.Through using ECAE asstrain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment,semi-solid billet with finespheroidal grains of 25μm can be prepared successfully.Compared with common SIMA,thixoformed satellite angle framecomponents using semi-solid billet prepared by new SIMA have higher mechanical properties at room temperature and hightemperature of 373 K.     

热压制工艺回收AZ91D镁合金屑的半固态组织演变(英文)

以从机械加工现场直接收集的AZ91D镁合金屑料为原料,采用热压制工艺再生制备半固态加工所需的坯料,研究二次加热过程中的半固态组织演变。结果表明,半固态组织演变可分为三个阶段:Mg17Al12相的溶解和Al原子的扩散,高溶质含量区域的熔化和固相颗粒的生成,固相颗粒的球化和长大。同时,在固相颗粒内部形成大量的嵌入式液滴。这种嵌入式液滴的数量和尺寸随着保温时间的变化而变化。随着保温时间的延长,固、液两相最终达到动态平衡,固相率不再发生变化。由于界面能降低和界面张力的作用使固相颗粒尺寸逐渐增大,并且越来越圆整。     

半固态铝合金AlSi6Mg2的二次加热工艺研究

针对半固态AlSi6Mg2合金的二次加热，实验优化了线圈和坯料的尺寸，保证了坯料加热过程中各个部位的温度均匀性；制定出单工位感应加热和六工位连续加热的二次加热工艺，在六工位连续操作过程中每个坯料加热11．5min，平均每2．3min提供一个加热完成的坯料，在工艺流程上实现了二次加热和半固态压铸的很好衔接。分析了二次加热过程中的组织演变．最终得到从坯料外形到内部组织都适合于半固态压铸的坯料。     

ZL101合金半固态二次加热

采用半固态合金二次加热，对半固态坯料施加合理的二次加热路径，重新获得适于后续加工的具有近球状固相颗粒均匀分布的半固态组织。采用功率为20kW，频率为30kHz的高频感应加热装置，研究了采用再熔融加热法制备的ZL101半固态合金坯料的二次加热过程。结果表明：为了获得适于最终成形的半固态组织，有必要把半固态坯料二次加热过程分为几个加热速率不同的加热阶段，然后在半固态温度区间某一需要加工温度下进行适度保温。通过实验给出了ZL101合金半固态坯料二次加热条件，并讨论了二次加热条件对半固态组织演化的影响。     

径向锻复合单向压缩变形式再结晶熔融法制备半固态坯料的研究

采用径向锻复合单向压缩变形式再结晶熔融(RFCUC-RAP)法和径向锻复合多向压缩变形式再结晶熔融(RFCMC-RAP)法对铝合金6063挤压棒料进行处理。对比分析了合金在直接半固态等温处理(SSIT)法、RFCUC-RAP法及RFCMC-RAP法三种工艺下微观组织的演化过程。结果表明：相比于直接SSIT法,采用RFCUC-RAP法和RFCMC-RAP法制备出的铝合金6063半固态坯料的晶粒尺寸明显减小,晶粒形状也有所改善。同时,由于变形过程相对简单,RFCUC-RAP法比RFCMC-RAP法更有优势,是一种有效的制备高质量半固态坯料的方法。     

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。     

半固态加工Al-Zn-Mg合金的组织演化

选用SIMA法制备的LC4合金及液相线凝固法制备的LC9合金为原料，研究了半固态加工Al-Zn-Mg合金的组织演化。由于这两种方法制备半固态坯料的机理完全不同，因此这两种材料加工后的组织演化规律截然不同：LC4合金的晶粒尺寸由于聚结而长大，而LC9合金的显微组织没有明显的变化。借助于扫描电镜和能谱分析，对半固态加工前后的显微组织进行成分分析，结果表明晶界处由共晶区、低熔点的富Cu区和杂质区三部分组成，且LC9合金的再加热组织的液相薄膜厚度大于CL4合金的；半固态加工后制件各部分的成分基本一致，证明半固态加工形成过程中材料的流动方式为层流。     

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

1Introduction Thixoforming is one of the best methods regarding manufacture of Mg-Al-Zn alloy components because of its low resistance of deformation compared with solid metal forging and high mechanical properties of formed components compared with liqui…     

触变模锻成形工艺对镁合金成形件力学性能的影响

采用半固态等温热处理法、近液相线模锻法和等通道角挤压法制备AZ91D—Y镁合金半固态坯料。分别将3种状态的坯料加热到半固态温度区间进行二次重熔后,进行了触变模锻成形。结果表明,在半固态温度为560℃,模锻压力为200MPa的条件下,半固态等温热处理法、近液相线模锻法和等通道角挤压法制备坯料分别保温30,20,15min后触变模锻获得最佳力学性能;随着坯料加热温度的升高,触变模锻成形件力学性能呈现先上升后下降的趋势;增加成形压力有利于触变模锻成形件力学性能的提高;在相同成形条件下,等通道角挤压法制备坯料触变模锻后的力学性能最好,近液相线模锻法次之,半固态等温热处理法较差。     

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.     

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.     

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%.     

Microstructure Evolution of Semi-Solid 7075 Aluminum Alloy During Reheating Process

Microstructural evolution of semi-solid 7075 Al alloy manufactured by strain-induced melt activation (SIMA) process was investigated. The effects of different processing parameters, such as isothermal temperature and holding time on the semi-solid microstructures (the liquid volume fraction, average grain size, and degree of spheroidization of the solid particles) during partial remelting have been investigated on 7075 Al alloy that was extruded by an extrusion ratio of 20 before remelting. Experiments of remelting were carried out in the range of 560-610 °C for 10, 20, and 30 min holding time and then the specimens were quenched in cold water. Microstructure of quenched samples were observed under optical microscope and then analyzed via image analysis. The results showed that high semi-solid isothermal temperature would increase the liquid volume fraction and accelerate the spherical processing of the solid particles. Furthermore at long holding time, the globular grains coarsened slightly and the average grains size are increased. The experimental results showed that the optimum process parameters, should be chosen at isothermal temperature of 580 °C with the holding time, <30 min.