SIMA制备半固态LY11合金的工艺研究

研究了应变诱发熔化激活法 (SIMA)制备半固态LY11合金过程中的变形温度、变形速度、等温温度和保温时间等工艺参数对LY11合金组织演变的影响。研究结果表明 ,要获得均匀、细小的非枝晶组织 ,必须合理地匹配SIMA工艺参数     

半固态LY11铝合金的组织演变研究

对LY11合金的应变诱发熔化激活法(SIMA)制备工艺进行了研究，定量分析了变形量(ε)、等温温度(Ti)、保温时间(t)等工艺参数和预处理技术对晶粒尺寸、分形维数和晶粒尺寸分布等的影响，讨论了晶粒的大小、形状、尺寸分布的演变规律。结果表明：变形量对晶粒大小、形状的变化影响极大，要获得细小、近球形的晶粒需足够的变形程度；升高等温温度和延长保温时间会促使晶粒长大、球化；所有试样的晶粒尺寸呈正态分布，随着变形量的减小、等温温度的升高和保温时间的延长，峰值点附近晶粒的数目逐渐减小，尺寸逐渐增加；冷、热变形预处理条件对组织演变产生一定的影响，给试样施加变形是SIMA工艺的必要步骤。     

LY11合金的半固态成形研究

研究了变形温度和应变速率对半固态和供应态LY11合金峰值流动应力、稳态流动应力以及微观组织的影响.由试验结果可知:变形温度对LY11合金的峰值应力影响显著,对稳态应力影响较小.应变速率对峰值应力的影响与变形温度有关.变形温度对微观组织的影响是:随着变形温度的升高,半固态LY11合金的近球状晶粒不断长大,供应态LY11合金的不规则细长晶粒逐渐向近球状转变,这种转变有助于改善材料的流动性能.     

Deformation characteristic of semi-solid ZCuSn10 copper alloy during isothermal compression

The compression tests were carried out by Gleeble-1500 thermo-mechanical simulator with samples of semi-solid ZCuSn10 alloy prepared by strain-induced melt activation(SIMA) process. The original microstructure and the deformation temperature of semi-solid ZCuSn10 alloy are different. The strain is 0.2, and the strain rate is 1 s~(-1) for the compression test. The results show that when the semi-solid ZCuSn10 alloy was prepared by SIMA process, the liquid fraction of semi-solid microstructure increases, and the solid grain is smaller,more uniform and more inclined to be round as the rolling pre-deformation increasing. The results also indicate that the deformation resistance of ZCuSn10 alloy in semi-solid state decreases with the deformation temperature increasing or the solid fraction of original microstructure decreasing. The stress–strain curves of the isothermal compression can be divided into quasi-elastic deformation stage and plastic deformation stage, and there are three deformation zones in the samples after isothermal compression, namely the difficult deformation zone, the large deformation zone and the free deformation zone. In the three deformation zones, the main deformation mechanism is flow of liquid incorporating solid particles(FLS)mechanism, plastic deformation of solid particles(PDS)mechanism and liquid flow(LF) combining with FLS mechanism, respectively.     

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.     

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.     

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 ℃。     

Preparation and thixoforging of semisolid billet of AZ80 magnesium alloy

Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed. The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation. Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA. Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape. The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.     

EFFECT OF PREDEFORMATION MANNER ON SEMI-SOLID STRUCTURE OF AZ61 MAGNESIUM ALLOY IN SIMA PROCESS

The effect of predeformation manner, predeformation ratio and isothermal heat-treat parameter on the non-dendrite structure of AZ61 magnesium alloy in SIMA process was studied. Under coequal heat-treat condition, the impact of the hot upsetting pre- deformation on semi-solid microstructure in SIMA process was compared with that of the cold compressive predeformation. The results indicate that non-dendrite microstructure in AZ61 magnesium alloy billets can be obtained by hot or cold upsetting predeformation in SIMA process, although their mechanisms of evolution are different. Increasing hot or cold upsetting predeformation ratio can enhance the effect and quality of the non-dendrite microstructure formed before storage energy up to saturation, but the proper isothermal temperature and holding time should be selected.     

半固态等温处理对Cu-Ca合金组织的影响

通过对比Cu-Ca合金铸态组织,研究了半固态等温处理主要工艺参数对半固态Cu-Ca合金组织的影响,得出了其半固态组织的演变规律。结果表明,在半固态等温处理工艺参数中,影响组织的主要参数为等温温度和保温时间。在一定选择范围内,随着等温温度的升高和保温时间的延长,组织将发生由树枝晶组织到非枝晶组织的一系列转变。研究发现,保温温度为957～967℃,等温时间为45～60min时,合金的球化效果最好,圆整度最高。     

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。     

Structure evolution of AZ61 magnesium alloy in SIMA process

The effect of prior compressive deformation, isothermal temperature and holding time on the structure of AZ61 magnesium alloy fabricated by strain-induced melt activation(SIMA) processing was investigated. The specimens were subjected under deformation ratios of 0%, 22% and 40% and various heat treatment time and temperature regions. The results indicate that the ideal technological parameters of semi-solid AZ61 alloy produced with non-dendrites are recommended as 22% (prior compressive deformation), 595℃ (heat treatment temperature) and 40 min(time). The as-cast AZ61 magnesium alloy isn‘t fit for semi-solid forming.     

7 A04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。     

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.     

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%.     

SIMA法处理AZ61热、冷压形变及半固态等温组织的比较研究

研究镁合金AZ61在SIMA法处理过程中压缩形变条件下,冷或热形变方式、形变率以及相应的等温热处理参数等对组织的影响规律。在同等热处理条件下,进行冷或热形变方式两套实验方案比较研究。结果表明,SI-MA法中,镁合金AZ61预变形采用热变形或冷变形均可得到细小非枝晶组织,虽演变机理不同,但在储存能趋于饱和之前,增加镁合金试样的热形变率或冷形变率,可以使热处理后非枝晶化效果和质量提高,但必须选择适当的等温热处理温度和保温时间。     

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.     

Microstructure development and thixoextrusion of magnesium alloy prepared by repetitive upsetting-extrusion

Thixoextrusion involves processing alloys with a spheroidal microstructure in the semi-solid state. Before thixoextrusion, repetitive upsetting-extrusion (RUE) is introduced into the strain induced metal activation (SIMA) process to predeform AZ80 magnesium alloy. Microstructure evolution of RUE formed AZ80 magnesium alloy during partial remelting is studied at temperatures for times. Tensile mechanical properties of thixoextruded components are determined and compared with those of AZ80 magnesium alloy thixoextruded from starting material produced by casting. The results show that with increasing number of RUE passes solid grain size decreases and the rate of liquation is improved. Prolonged holding time results in grain coarsening and the improvement of degree of spheroidization. The variation of the solid grains with holding time obeys the Lifshitz, Slyozov and Wagner law. Increasing the heating temperature is favorable for the formation of spheroidal solid grains. The tensile properties for AZ80 magnesium alloy thixoextruded from starting material produced by RUE are better than those of AZ80 magnesium alloy thixoextruded from starting material produced by casting.     

半固态LY11合金的压缩变形

研究了变形温度和应变速率对半固态LY11合金变形行为和微观组织的影响.研究结果表明:在液固温度区间变形时,变形温度、应变速率对半固态LY11合金的流变应力峰值影响显著,对稳态流变应力影响较小.对微观组织的影响是:随着变形温度的升高和应变速率的降低,固相晶粒尺寸增大,但仍保持初始的近球状.在半固态合金的压缩过程中,随着工艺参数的变化,占主导地位的变形机制也随之变化.