SIMA法制备半固态AM60-2Nd镁合金组织的演变

主要研究了等温温度和等温时间对应变诱导熔化激活法制备的半固态AM60-2Nd合金组织演变的影响。结果表明,在230℃以45%的压缩比压缩变形后,组织呈明显的纤维流线状,针状Al_(11)Nd_3相被拉长、碎断成颗粒状不连续分布在晶界上。随着等温温度的升高或等温时间的延长,固相颗粒圆整度增加,固相率减少。固相颗粒尺寸随等温温度的升高先减小后增大,随时间的延长一直增大。综合考虑,在590℃保温17~20 min或600℃保温15 min可获得最佳的半固态球状组织。在等温处理期间,呈颗粒状弥散分布的Al_(11)Nd_3相在高温下对晶界有明显的钉扎作用,通过阻碍再结晶过程以及减慢Ostwald熟化速度,获得细小的半固态球状组织。     

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0.5%富铈混合稀土AZ91D镁合金半固态组织的形成

半固态浆料的固相颗粒尺寸、形态和分布主要取决于熔化过程中液相的形成与演化过程。采用添加0.5%富铈混合稀土来改善AZ91D镁合金的铸态组织,研究在半固态等温热处理中的组织演变以及非枝晶组织制备与控制的机理。结果表明:稀土合金化处理可促进初生相在等温热处理过程中由枝晶向粒状晶的转变,可获得更加细小、均匀的球状固相颗粒,并且其粗化速度较慢。半固态等温热处理过程中,整个系统处于熔化和结晶的动态平衡,铸态组织中枝晶根部高溶质浓度区或系统的温度、浓度起伏是固相颗粒内液相形成的内在和外在条件。     

半固态等温处理对AM60B镁合金组织的影响

研究了半固态等温处理工艺对金属型AM60B的组织和初生相尺寸及形态的影响.结果表明,在半固态等温热处理过程中,网状分布的共晶组织先发生熔化;随着等温时间的延长,α相发生熔化分离;等温时间过长时,球状颗粒有长大、合并的趋势,等温温度越高,晶粒间的合并现象越严重.结果表明,在595 ℃时保温60～75 min可以获得较好的球状非枝晶组织;经过两步法短时的高温保温,非枝晶转变进程加快,可以得到较细小均匀的非枝晶组织.     

AZ91D镁合金在半固态等温热处理中的组织演变

研究了未变质处理和变质处理的AZ91D镁合金在半固态等温热处理过程中的组织演变,并对其组织演变机理进行了探讨。结果表明：AZ91D镁合金在液－固相区570℃等温处理时,未变质处理的δ相由粗大的树枝晶演变为大块状,随后δ相发生熔化分离,并在半固态等温过程中演变为球状,产生相最小尺寸可达50－80μm;变质处理的初生δ相由等轴晶演变为小块状,随后进一步熔化分离为更细小的斑块,接着逐渐演变为球状组织,初生相最小尺寸可达20－60μm。等温处理时间过长时,两种组织都会发生合并长大。     

等温温度和时间对ZL104铝合金半固态等温热处理组织的影响

研究了半同态等温热处理制备非枝晶组织ZL104铝合金的可行性以及保温温度和时间对合金半固态等温热处理组织的影响.结果表明,通过合适的半固态等温热处理工艺制备非枝品球状组织ZL104铝合金是可能的.在580℃保温下随着保温时间从30 min延长到120 min或在120 min保温下随着从570 oC保温提高到580℃,合金半固态组织巾未熔初生相颗粒的尺寸减小,其球状化趋势逐渐变得更明显.在本文条件下,ZL104合金最佳的半固态等温热处理工艺为580℃×120 min,通过该工艺合金可以获得液相含量为49%和未熔固相颗粒尺寸为115μm的非枝品球状组织,能够满足后续半固态成形的需要.     

Mg-6Zn-1Cu-0.5Ce镁合金的非枝晶组织演变及机理

半固态金属坯料部分重熔是半固态金属触变成形工艺的重要技术环节,采用等温热处理法对Mg-6Zn-1Cu-0.5Ce镁合金在部分重熔过程中的非枝晶组织演变过程和机理进行研究。结果表明:在半固态重熔初始阶段,Mg-6Zn-1Cu-0.5Ce合金沿晶界分布的共晶相逐渐向α-Mg基体中扩散溶解,达到共晶熔化温度后,剩余部分开始熔化。随着保温时间的进一步延长,为了降低系统的界面能,颗粒将发生合并长大。其中,非枝晶颗粒的分离是由液相沿亚晶界浸渗和根部重熔两种机制起主导作用。Mg-6Zn-1Cu-0.5Ce合金的最佳等温热处理工艺为保温温度600℃和保温时间25 min,采用该工艺处理后所得非枝晶颗粒平均尺寸为57μm,形状因子为1.16,固相率为68%。     

等温热处理对Mg-6Zn-3Cu合金半固态组织演变的影响北大核心CSCD

通过半固态等温热处理,研究了重熔温度和保温时间对铸造ZC63镁合金半固态组织演变的影响。结果表明:半固态等温热处理能够将ZC63合金中的枝晶组织转变为球状组织,并可获得更加细小、分布均匀的球状颗粒;重熔温度和保温时间对非枝晶组织演变有着重要的影响,提高保温温度或延长保温时间,可加快原始铸锭重熔进程及组织形态的优化,保温温度过高或保温时间过长,试样会发生严重变形,同时球状颗粒易于粗化和长大;非枝晶组织演变是在熔化和结晶的动态变化中完成,主要的演变机制是在等温热处理过程中晶界处的共晶组织向基体溶解,原始组织的粗化、分离、球化以及球状颗粒的合并与长大。ZC63合金半固态触变成形最适合的等温热处理工艺是600℃×30 min。     

等温热处理对Mg-6Zn-3Cu合金半固态组织演变的影响

通过半固态等温热处理,研究了重熔温度和保温时间对铸造ZC63镁合金半固态组织演变的影响。结果表明:半固态等温热处理能够将ZC63合金中的枝晶组织转变为球状组织,并可获得更加细小、分布均匀的球状颗粒;重熔温度和保温时间对非枝晶组织演变有着重要的影响,提高保温温度或延长保温时间,可加快原始铸锭重熔进程及组织形态的优化,保温温度过高或保温时间过长,试样会发生严重变形,同时球状颗粒易于粗化和长大;非枝晶组织演变是在熔化和结晶的动态变化中完成,主要的演变机制是在等温热处理过程中晶界处的共晶组织向基体溶解,原始组织的粗化、分离、球化以及球状颗粒的合并与长大。ZC63合金半固态触变成形最适合的等温热处理工艺是600℃×30 min。     

Mg-2Zn-0.5Y镁合金半固态等温处理过程中的微观组织演变

本文研究了挤压Mg-2Zn-0.5Y合金在半固态等温处理过程中的微观组织演变规律。结果表明：挤压态的Mg-2Zn-0.5Y合金包含α-Mg,I相和W相三种物相,并且平均晶粒尺寸为7μm。在温度为793K的半固态等温热处理过程中,晶粒不断长大,直到保温时间达到4min时才出现液相。随着等温处理温度和时间的增加,α-Mg固相颗粒不断长大,并且逐步被液相分离;同时,出现在晶界的液相与颗粒内部的液滴都在不断地增多。研究还发现,当固相率较高的时候,晶粒间的合并机制与固相颗粒再熔化机制同时起主导作用;然而当固相率较低的时候,Ostwald熟化机制是主要的粗化机制,同时也可以观察到晶粒间的合并。     

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.     

Effect of La addition on semi-solid microstructure evolution of Mg-7Zn magnesium alloy

Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment. The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated. Meanwhile, the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied. Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure. During the semi-solid thermal transformation, the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time. The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605 °C for 30 min is the optimal. The average size of solid particles, shape factor, and solid fraction are 42 µm, 1.45 and 61.8%, respectively. At the same time, a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.

     

Effect of Semi-Solid Isothermal Heat Treatment on Microstructure of ZL104 Aluminum Alloy

The feasibility of fabricating ZL104 aluminum alloy with non-dendritic microstructure by 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, are investigated. The research results indicate that it is possible to produce ZL104 alloy with non-dendritic microstructure by a suitable semi-solid isothermal heat treatment. After treated at 580 ℃ for 120 min, the ZL104 alloy can obtain a non-dendritic mic...     

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。     

Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy

The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.     

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.     

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…     

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。     

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 ℃。