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。     

基于ADAM温控系统稀土铝铜合金重熔工艺研究

采用ADAM4000系列模块开发的温度控制系统,实现了温度信号采集、交换和控制。研究了在稀土铝铜合金半固态重熔过程中加热温度和保温时间对合金组织的影响,并对组织演化机制进行了探讨。实验表明,加热温度和保温时间是影响晶粒尺寸和均匀性两个重要的因素。稀土铝铜合金半固态重熔合适工艺参数为:加热温度630℃,保温时间20min。重熔过程中α晶粒合并和Ostwald长大是微观组织变化的主要机制。     

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.     

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。     

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.     

形变诱导法半固态加热工艺参数对LY12合金组织和晶粒尺寸的影响

对LY12合金采用形变诱导法制备半固态合金料坯的组织演变过程进行了观察，对变形率、半固态温度、半固态保温时间对合金半固组织和晶粒尺寸的影响进行了研究。组织演变过程观察表明：用形变诱导法制备该合金半固态坯料的合适的半固态重熔温度为618℃；合金在该温度重熔过程中，形变带状组织首先分解为细小的a多边形晶粒，随保温时间的延长，晶粒尺寸逐渐变大，同时a相逐渐球化；在相同的半固态温度和相同的保温时间下，宏观变形率大的晶粒尺寸要比变形率小的合金组织晶粒尺寸小；变形率大的试样比变形率小的液相出现时间早；在同一宏观变形率下，试校内部微观形变大的部位晶粒尺寸要比形变小的部位晶粒尺寸小。     

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℃.     

半固态Al-4Cu-Mg合金的变形行为及组织演化

以热模拟压缩实验为基础,研究了变形工艺参数(包括变形温度、应变速率和变形程度)对半固态Al-4Cu-Mg合金变形力学行为和微观组织的影响.研究结果表明:半固态Al-4Cu-Mg合金的流变应力峰值对变形温度和应变速率的变化比较敏感;变形温度和应变速率对稳态流动应力影响较小.应变速率对流变应力峰值的影响与变形温度有关.变形工艺参数对微观组织的影响为:随着变形温度的升高和应变速率的减小,α相晶粒平均尺寸增大,半固态Al-4Cu-Mg合金变形后的组织仍保持近球状组织,这与变形过程中固态α相的流动方式有关.     

Ti14合金半固态等温热处理过程中的组织演化规律

研究了Ti14合金在1000和1050 ℃半固态下,不同保温时间微观组织的演化过程,计算不同半固态温度下晶粒的生长指数,并分析半固态温度和保温时间对晶界和晶粒尺寸以及形态的影响规律.结果表明:随着保温时间的延长,晶粒明显长大,晶粒形态趋于圆整,晶界处液相由不连续分布转变为连续分布最终呈网格状;1000和1050 ℃对应的晶粒生长指数分别为0.88和0.97,表明温度的升高加速了微观组织的演化.     

SIMA法制备7A04合金半固态触变组织的演化

研究了二次加热工艺参数对SIMA法制备7A04合金半固态触变组织的演化规律.结果表明:随着加热温度的升高和保温时间的延长,晶粒的形状逐渐趋于球形.当加热温度低于610℃时,晶粒尺寸不断长大,而后逐渐减小.在保温的初始阶段,共晶液相没有完全浸润晶粒边界,晶粒的聚结长大处于主导地位.当保温时间达到4min左右时,共晶液相几乎充满了所有的晶界,Ostwald长大扩散机理处于主导地位.晶粒长大规律符合动力学方程.     

Microstructure and Element Distribution during Partial Remelting of an Al-4Cu-Mg alloy

The effects of the isothermal temperature and holding time on the microstructure and element distribution have been investigated during partial remelting of the semisolid Al-4Cu-Mg alloy. The experimental results show that the optimal process parameter should be chosen at isothermal temperature of 540-580 °C with the holding time of less than 10 min. Coalescence and coarsening of α grains occur at low liquid fraction. At high liquid fraction, coarsening of α grains and melting of small grains were promoted by an increase of the isothermal temperature and the holding time. The coalescence of grains and Ostwald ripening are two main mechanisms of the microstructural evolution during partial remelting. Meanwhile, the higher the isothermal temperature and the longer the holding time, the more segregation of Cu at the grain boundary would be, which conform to the theory of element distribution affected by heating condition.     

Effects of isothermal heat treatment on microstructural evolution of semisolid Al-4Cu-Mg alloy

The authors investigated the effects of the isothermal heat-treatment conditions on the microstructural evolution and composition distribution of semisolid Al-4Cu-Mg alloy during isothermal heat treatment. The experimental results show that the microstructural evolution and composition distribution of semisolid Al-4Cu-Mg alloy are controlled by atom diffusion during the isothermal heat treatment process. Grain growth and spheroidization were promoted with the increase of the isothermal temperature and/or the holding time. Moreover, the higher the isothermal temperature, or the longer the holding time, the more segregation constituent elements occurred to the grain boundaries. The low melting structure at grain boundary is greatly affected by Cu. The microstructural evolution in the isothermal heat-treatment process is as follows: recovery, recrystallization, fragmentation, spheroidization, and coarsening. Such fragmentation, spheroidization, and grain growth of coalescence and Ostwald ripening are involved as main mechanisms in the isothermal heat-treatment process.     

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.     

铝合金半固态变形时的微观组织特征

文章在铝合金半固态压缩实验的基础上,深入研究了不同工艺参数下Al-4Cu-Mg合金半固态压缩时的微观组织形貌及参数变化。研究结果表明,半固态压缩时的微观组织特征受变形工艺参数的影响较大。变形程度越大,晶粒尺寸越小,晶粒圆整度越差。变形程度超过40%,晶粒尺寸急剧减小,变形机制发生了显著变化。随着应变速率的减小,晶粒尺寸增大,晶粒逐渐趋于圆整。在较高的变形温度下,晶粒发生了合并长大。但过高的变形温度引起晶粒尺寸的急剧增大,对变形不利。     

Application of cyclic upsetting-extrusion to semi-solid processing of AZ91D magnesium alloy

The microstructural evolution of AZ91D magnesium alloy prepared by means of the cyclic upsetting-extrusion and partial remelting was investigated. The effects of remelting temperature and holding time on microstructure of semi-solid AZ91D magnesium alloy were studied. Furthermore, tensile properties of thixoextruded AZ91D magnesium alloy components were determined. The results show that the cyclic upsetting-extrusion followed by partial remelting is effective in producing semi-solid AZ91D magnesium alloy for thixoforming. During the partial remelting, with the increase of remelting temperature and holding time, the solid grain size increases and the degree of spheroidization tends to be improved. The tensile mechanical properties of thixoextruded AZ91D magnesium alloy components produced by cyclic upsetting-extrusion and partial remelting are better than those of the same alloy produced by casting.     

Deformation Behavior and Constitutive Equation Coupled the Grain Size of Semi-Solid Aluminum Alloy

Isothermal compression tests on Al-4Cu-Mg alloy were carried out in semi-solid state. Deformation behavior and microstructural evolution are discussed in this paper. Meanwhile, a new constitutive equation, which couples the grain size and liquid volume fraction, has been established for the semi-solid deformation behavior. The results show that the maximum difference between the calculated with the experimental data is less than 15%. The present equation is satisfactory for describing the correlation between the flow stress and microstructure of semi-solid Al-4Cu-Mg alloy. The coupled simulation of the deformation behavior and microstructural evolution during the semi-solid forming would be conducted easily through writing the present equation in a FE code.     

Deformation and microstructure characterization during semi-solid extrusion of Al-4Cu-Mg alloy

Effects of the process parameters, including deformation temperature, punch velocity and extrusion ratio, on the deformation and microstructure characterization during the semi-solid extrusion of Al-4Cu-Mg alloy, were investigated. The experimental results show that the load decreases with an increase of deformation temperature and/or a decrease of punch velocity. When the displacement is more than 4 mm, the load decreases significantly with an increase of the deformation temperature, which is related to the high liquid fraction. The microstructure varies with the process parameters and deformation regions. It can be found that the dynamic recovery occurs during the semi-solid extrusion of Al-4Cu-Mg alloy at lower deformation temperature. Subsequently, the microstructure elongated gradually polygonizes with an increase of deformation temperature. So, the higher deformation temperature should be chosen during the semi-solid extrusion of Al-4Cu-Mg alloy because the grains polygonized and high liquid fractions are beneficial to deformation.     

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.     

Microstructure and tensile properties of AM50A magnesium alloy prepared by recrystallisation and partial melting process

Prior to thixoextrusion, the microstructural evolution of semi-solid AM50A magnesium alloy prepared by the recrystallisation and partial remelting (RAP) route was investigated. The effect of compressive ratio on microstructure of semi-solid AM50A magnesium alloy was studied. Furthermore, tensile properties of thixoextruded components were determined. The results showed that the occurrence of recrystallised grains was closely associated with the location of the first liquid formed above the solidus. With prolonging holding time, deformed microstructure was penetrated, causing fragmentation, which resulted in the decrease of average grain size. Moreover, prolonging holding time was favorable for the improvement of the degree of spheroidization due to the increase in the amount of liquid. With the increase in compressive ratio, the size of solid grain decreased, the degree of spheroidization was improved during partial remelting, and the tensile properties of thixoextruded AM50A components were improved. The tensile properties for AM50A magnesium alloy thixoextruded from starting material produced by the RAP route were better than those of the same alloy produced by die-casting and thixomolding.     

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。