等温热处理对Mg-Gd-Zn-Zr合金半固态组织的影响

选择稍高于共晶反应温度作为等温热处理温度,对铸态Mg-15Gd-2Zn-0.6Zr合金进行等温热处理,获得了半固态球化组织。研究了热处理温度和保温时间对半固态组织的影响,探讨了半固态组织演变机制及适用于低温等温热处理的半固态Mg-Gd-Zn-Zr合金成分设计。结果表明,液相组织具有低的温度敏感性,其组织演变主要机制为α-Mg表面熔化和α-Mg动态再析出,而固相颗粒球化机制为:α-Mg树枝晶→枝晶臂粗化→枝晶臂合并、不规则多边形化→球化。     

等温热处理对AZ91D+Ce镁合金半固态组织的影响

研究了等温热处理对AZ91D+Ce镁合金半固态组织的影响,获得了较理想的球状或类球状晶粒组织。结果表明,在等温热处理的过程中,加入稀土Ce会阻碍原子向固相粒子聚集和结合,抑制固相颗粒的长大,形成细小圆整的半固态组织。随等温热处理温度的升高,原子活动能力增强,熔化速度加快,液相量增加,固相颗粒尺寸先减小后增大。在等温初始阶段,熔化对初生固相颗粒尺寸起决定作用,使得颗粒尺寸减小。但是,随等温时间的进一步增加,由于合并粗化和Ostwald熟化的作用,固相颗粒开始长大。     

等温热处理过程中铸态AZ91镁合金的微观组织演化

铸态AZ91镁合金加热至液固相温度区间内等温热处理后演变成半固态金属,对淬火组织形态分析的试验表明:在高固相体积分数条件下,网状分布的共晶组织首先熔化,二次枝晶臂消失或熔断脱落并重新沉淀在枝晶主干上,在Gibbs-Thomson效应下,发生Ostwald熟化,固相颗粒由枝晶逐渐演变成球形颗粒,并随着热处理时间的延长发生合并现象,而且热处理温度越高晶粒间合并现象越严重。同时在界面能降低的驱使下,晶粒内部包裹的液滴以两种方式形成:晶粒内富Al、Zn的质点经过熔化、扩散、合并、或者脱落的二次枝晶臂沉淀后搭桥生长形成。     

半固态等温热处理对铸态AZ80镁合金组织的影响

研究了等温热处理温度和保温时间对铸态AZ80镁合金半固态组织演变的影响.研究结果表明:在热处理过程中,随保温时间的延长,初生α相演变过程是,首先由大部分粗大的树枝晶二次枝晶臂合并成为大块状,而后大块状晶粒在晶粒内部及晶界处液相和固液界面的曲率共同作用下熔化分离为小块状,继续保温则圆整化;保温时间相同,等温处理的温度越高,枝晶演变过程越快,保温温度越高或保温时间越长,球状晶粒也容易趋于长大.AZ80镁合金半固态成形所需的最佳工艺条件为加热温度570℃左右,保温时间30min.     

基于消失模铸造的AZ91镁合金组织改性研究

研究了机械振动处理技术对AZ91合金在消失模铸造条件下的组织形貌的影响,以及该铸态组织在半固态等温热处理过程中的组织演变,并探讨了振动细化机理和组织演变机理。结果表明:机械振动能显著地细化AZ91合金的铸态组织;在液固相区570℃等温处理时,其铸态组织都能由枝晶转变为球状晶组织,而且振动处理可获得更加细小并且均匀的球状组织。等温处理时间过长时,两种组织都会发生合并长大。     

添加Al-Ti-B的Mg-20Al-0.8Zn半固态组织的形成机理

利用添加质量分数为0.4%的Al-Ti-B中间合金来改善Mg-20Al-0.8Zn镁合金的铸态组织,研究了该合金在半固态等温处理过程中的组织演变以及非枝晶组织的制备与控制.结果表明,Al-Ti-B能显著减小铸态Mg-20Al-0.8Zn合金的晶粒尺寸,且经过Al-Ti-B细化处理的Mg-20Al-0.8Zn合金在半固态等温热处理过程中可获得更加均匀、细小的球状固相颗粒,固相颗粒的粗化速度较慢.试验得到的半固态组织中固相颗粒的平均尺寸为55～65 μm.试验表明,采用等温处理(450℃+保温90～120 min;465℃+保温90 min或485℃+保温60～90 min)能够得到更适合触变成形的半固态浆料,其半固态浆料的组织更加均匀、晶粒更加细小.     

半固态等温处理制备非枝晶组织YL112压铸铝合金的研究

通过工艺试验和组织分析相结合的办法,对半固态等温处理制备非枝晶组织YL112压铸铝合金进行了初步的研究.研究结果表明:半固态等温热处理能有效地使YLL12压铸铝合金的铸态枝晶组织转变为非枝晶组织,其中提高等温温度有利于合金铸态枝晶组织的熔断和粒状非枝晶组织的形成,而延长保温时间则有利于提高合金粒状非枝晶组织的圆整度.     

等温热处理对ZC61-0.3Cr镁合金半固态组织演变的影响

研究等温热处理温度和保温时间对ZC61-0.3Cr镁合金半固态组织演变的影响。结果表明:在等温热处理过程中,ZC61-0.3Cr合金中的原始树枝晶组织能够转变为半固态非枝晶组织,得到均匀、圆整的球状颗粒。随着保温温度的升高,合金中的原始树枝晶组织经过初始粗化、组织分离和球化演变成半固态非枝晶组织;随着保温时间的延长,晶界处的(α-Mg+MgZn2+CuMgZn)共晶组织优先熔化,合金中的大块状组织逐渐演变为球状组织;但是,保温温度过高或保温时间过长,都会引起球状颗粒的粗化长大。在粗化长大过程中,合并长大机制和Ostwald熟化机制同时存在,共同影响固相颗粒的形貌和尺寸大小。ZC61-0.3Cr镁合金半固态成形所需的最佳工艺条件为(585℃, 30 min);此条件下,其颗粒平均尺寸、形状因子和固相率分别为43μm、1.4和51%。     

添加AI—Ti—B的Mg-20AI-0．8Zn半固态组织的形成机理

利用添加质量分数为0．4％的AI—Ti—B中间合金来改善Mg-20AI-0．8Zn镁合金的铸态组织,研究了该合金在半固态等温处理过程中的组织演变以及非枝晶组织的制备与控制。结果表明,AI-Ti-B能显著减小铸态Mg-20AI-0．8Zn合金的晶粒尺寸,且经过AI-Ti-B细化处理的Mg-20AI-0．8Zn合金在半固态等温热处理过程中可获得更加均匀、细小的球状固相颗粒,固相颗粒的粗化速度较慢。试验得到的半固态组织中固相颗粒的平均尺寸为55～65μm。试验表明,采用等温处理（450℃＋保温90～120min;465℃＋保温90min或485℃＋保温60～90min）能够得到更适合触变成形的半固态浆料,其半固态浆料的组织更加均匀、晶粒更加细小。     

Al-5.8%Cu合金半固态浆料的控制熔化制备法

研究了具有枝晶组织的Al-5.8%Cu合金在控制熔化过程中固相形态的演变,以及加热速率、保温时间对固相形态演变的影响.分析了影响熔化组织中固相形态的因素,提出由枝晶组织直接获得适合半固态成形的球晶组织的控制熔化工艺,并制备了固相颗粒圆整、尺寸较小、分布均匀的半固态浆料.     

Effects of semi-solid isothermal process parameters on microstructure of Mg-Gd alloy

The effects of semi-solid isothermal process parameters on the microstructure evolution of Mg-Gd rare earth alloy produced by strain-induced melt activation(SIMA)were investigated.The formation mechanism of the particles in the process of the isothermal treatment was also discussed.The results show that the microstructure of the as-cast alloy consists ofα-Mg solid solution, Mg5RE and Mg24RE5(Gd,Y,Nd)phase.After being extruded with an extrusion ratio of 14:1 at 380℃,the microstructure of Mg-Gd alloy changes from developed dendrites to near-equiaxed grains.The liquid volume fraction of the semisolid slurry gradually increases with elevating isothermal temperature or prolonging isothermal time during the partial remelting.To obtain an ideal semisolid slurry,the optimal process parameters for the Mg-Gd alloy should be 630℃for isothermal temperature and 30 min for the corresponding time,respectively,where the volume fraction of the liquid phase is 52%.     

Microstructural evolution and tensile mechanical properties of thixoformed AZ91D magnesium alloy with the addition of yttrium

The microstructure evolution of AZ91D magnesium alloy in the semi-solid state has been proposed or reported in previous literature. However, no detailed investigation has been conducted regarding the relationship between the microstructure and tensile mechanical properties of the thixoformed AZ91D magnesium alloy. In this paper, the microstructure of AZ91D alloy with the addition of yttrium was produced by the semi-solid thermal transformation (SSTT) route and the strain-induced melt activation (SIMA) route, respectively. Isothermal holding experiments investigated grain coarsening and the degree of spheroidization as a function of holding time in the semi-solid state. The SSTT route and the SIMA route were used to obtain the semi-solid feedstock for thixoforming. The results show that solid particles of the SSTT alloy are spheroidized to some extent but the previous irregular shape is still obvious in some of them. While the SIMA alloy exhibits ideal, fine microstructure, in which completely spheroidized solid particles contain little entrapped liquid. The microstructure of the SSTT alloy is less spheroidized compared with the SIMA alloy under the similar isothermal holding condition. As the holding time increases, the mean solid particle size of the SSTT alloy decreases initially, then increases, while the mean solid particle size of the SIMA alloy increases monotonously at 560 °C. Compared with the SSTT alloy, the SIMA alloy obtains finer grains under the similar isothermal holding condition. The mechanical properties of the thixoformed AZ91D alloy with the addition of yttrium produced by the SIMA route are better than those of the thixoformed alloy produced by the SSTT route. The ultimate tensile strength, yield strength and elongation for the thixoformed alloy produced by the SIMA route are 303.1 MPa, 147.6 MPa and 13.27%, respectively. The tensile properties for the AZ91D alloy with the addition of yttrium thixoformed from starting material produced by the SIMA route are better than those of the AZ91D alloy with the addition of yttrium thixoformed from starting material produced by the SSTT route.     

The effect of rare earth elements on the kinetics of the isothermal coarsening of the globular solid phase in semisolid AZ91 alloy produced via SIMA process

In the present study, the effects of rare earth (RE) elements on the microstructure and coarsening kinetics of the solid globular particle in the semisolid slurry of AZ91 magnesium alloy have been studied at 570 °C and 580 °C. The results showed that the coarsening kinetics of the solid globular particles in semisolid slurry of AZ91 alloy satisfies the Ostwald ripening theory. It was shown that the coarsening rate of the solid particles decreases by adding RE elements into AZ91 alloy, specially at 580 °C, which results in the smaller particles size. It was attributed to the solid–liquid interfacial energy reduction due to the addition of RE elements.     

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。     

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…     

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。     

Influence of rare earth element Ce and La addition on corrosion behavior of AZ91 magnesium alloy

Two types of AZ91 magnesium alloys containing rare earth element Ce or La were fabricated. Hydrogen evolution and electrochemical tests were carried out to evaluate the corrosion behavior of new AZRE (RE = Ce or La) and AZ91 alloys in 3.5% NaCl solutions (pH 6.50). Various corrosion rate tests indicated that addition of RE obviously enhanced corrosion resistance of AZ91 magnesium alloy. The optimal content of RE was 0.92% for Ce and 0.66% for La. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and low‐angle X‐ray diffraction (XRD) were used to characterize the effect of RE addition on microstructure and corrosion product film of AZ91 magnesium alloy. The refined β phase and formation of γ phase in AZRE alloy were observed by SEM, which resulted in the improvement of corrosion resistance due to the depression of microgalvanic couples. Moreover, the enhanced protective effectiveness of corrosion products was another reason for the improved corrosion resistance.     

Microstructural evolution of equal channel angular pressed AZ91D magnesium alloy during semi-solid isothermal heat treatment

The microstructural evolution of AZ91D magnesium alloy processed by equal channel angular pressing during isothermal heat treatment at 570℃ was investigated. The results indicated that the equal channel angular pressing followed by semi-solid isothermal heat treatment was an effective method to prepare semisolid nondendritic slurry of AZ91D magnesium alloy. During this process, its microstructure change underwent four stages, the initial coarsening stage, the structure separation stage, the spheroidization stage and the final coarsening stage. The microstructural spheroidization effect was the best after being heated for 15 min for the alloy pressed for four passes, and the grain size was the smallest. With the further increase of heating time, the grain size and shape factor increased. When the heating time was kept constant, the grain size and shape factor decreased with the increase of pressing passes.     

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.