液相线半连续铸造7075Al合金二次加热与触变成形

研究了液相线半连续铸造的7075Al合金半固态浆料在不同温度下的液固相比、二次加热组织、触变成形性,以及热处理前后成形件的力学性能。结果表明,7075Al合金触变成形液相比为30%-50%时对应的温度区间为600-620℃,二次加热可以将液相线半连续铸造7075Al合金锭坯中的蔷薇状和近球状组织转化为球形晶粒组织,适合于半固态加工,组织最佳的条件是加热温度580℃左右,保温时间15-30min,及加热温度600℃左右,保温时间5-15min.加热到600℃,保温15min后7075合金流动性成形性非常好,闭模锻造完全可以半固态成形,未经热处理的7075Al合金成形件强度极限达357.9MPa,T6热处理后强度极限达468MPa。     

A380铝合金半固态坯料二次加热工艺及组织演变

研究了近液相线铸造A380铝合金在563、573及583℃保温5~60min的二次加热工艺条件下的组织演变。结果表明,随着保温温度的升高和保温时间的延长,晶粒平均等积圆直径增加,晶粒圆整度降低,温度越高,变化的趋势越快。半固态坯料加热温度为583℃,保温时间为20min时,能够获得较好的二次加热组织。此时,晶粒平均等积圆直径为49.74μm,晶粒平均圆整度为1.75。     

原位TiC颗粒含量对近液相线铸造7075铝合金二次加热组织的影响

采用原位反应近液相线铸造法制备具有不同原位TiC颗粒含量的TiC_p/7075铝基复合材料,在7075铝合金固-液两相区间(477～635 ℃)的580和600 ℃进行二次加热并保温20 min,水淬固定其半固态组织,应用Image Pro Plus软件测量平均晶粒尺寸及形状因子,研究原位TiC颗粒含量对该合金二次加热组织的影响.结果表明:当原位TiC颗粒质量分数为0～4.4%时,随着原位TiC颗粒质量分数增加,合金铸态组织直接转变为等轴晶组织,且在二次加热过程中,原位TiC颗粒对晶粒的长大行为具有明显的抑制作用;在相同的二次加热条件下,4.4%TiC_p/7075铝基复合材料的平均晶粒尺寸比7075基体合金的减少30～40 μm,更加适合于半固态触变成形.     

液相线半连续铸造112Al合金的组织

液相线半连续铸造是 1种先进的半固态浆制备方法。考察了铸造温度、冷却强度及铸造速度对液相线半连续铸造法制备 112铝合金半固态浆料组织的影响。合金熔体在常规铸造温度 (690℃ )下浇注获得的锭坯边部是粗大的枝晶 ,中间部位组织极不均匀 ;在接近液相线温度以上 (60 5℃ )保温 2 0min后浇注的铸造组织较好 ,中心部位和边部组织的差异较小。在液相线温度 (5 88℃ )保温 2 0min后进行半连续铸造获得的锭坯中心和边部组织元均是均匀、细小的近球形组织。降低一次冷却强度、增大二次冷却强度和减小铸造速度均有利于均匀、细小、等轴的半固态组织的形成。结果表明 ,液相线半连续铸造能有效地制备 112Al合金的半固态浆料     

7075Al合金液相线半连续铸造组织及形成机理

研究了液相线半连续铸造法制备7075Al合金半固态浆料的组织，合金熔体在常规铸造温度（720℃）下浇注获得的锭坯边部是粗大的枝晶，中间部位组织极不均匀；在接近液相线温度（642℃）保温30min后的铸造组织较好，中心部位和边部组织的差异较小，在液相线温度附近（638℃）保温后进行半连续铸造获得的锭坯中心和边部组织均是均匀、细小的近球形组织。一次冷却强度的降低、二次冷却强度的增大和铸造速度的减小有利于均匀、细小的近球形组织的形成，熔体中大量内生形核和固-液界面成分过冷的降低有利于上述组织的形成，结果表明，液相线半连续铸造是一种有效的半固态浆料的制备方法。     

AlSi7Cu5合金斜板近液相线铸造组织分析

研究了斜板近液相线铸造AlSi7Cu5合金微观组织及其二次加热过程中的变化。‘实验表明，冷却方式、浇注模具和浇注方式对合金微观组织有明显的影响。近液相线温度下水冷斜板铜模浇注的AlSi7Cu5合金组织为细小均匀的等轴晶，晶粒平均直径为55．2μm，晶粒平均圆度为2．13。在580℃下恒温25min左右，可得到适合触变成形的二次加热组织。     

近液相线法铸造非枝晶A356合金组织与成形性能

用近液相线半连续铸造法制备出具有等轴晶粒的半固态A356合金坯料，合适的铸造工艺为铸造温度615℃，保温20min,铸造温度120mm/min，冷却水流量0.086m^3/min，在电阻炉加热的条件下，半固态A356合金坯料的重熔加热温度场均匀，合适的加热温度为580-590℃，在模具温度400-600℃的条件下，触变成形汽车发动机用轴瓦盖热处理后的σ值达到290.2MPa，δ5达到12.9%。     

铸造速度对ZL116合金半固态坯料组织的影响

采用近液相线半连续铸造技术制备ZL116合金半固态坯料,研究了铸造速度对半固态坯料微观组织形成的影响,研究表明,ZL116合金采用近液相线半连续铸造工艺,当铸造速度为150~200mm/min时,可获得分布均匀、细小的蔷薇状半固态坯料组织。     

原位反应TiC颗粒对液相线铸造法制备半固态铝合金组织的影响

采用原位反应液相线铸造法制备7075＋X％TiC（体积分数X=0、0．8、1.0、2．0）半固态铝合金坯料,选择590℃对其进行二次加热实验,保温时间分别为5、20、30min,并与液相线铸造7075铝舍金的相同条件下的组织相比．探索原位TiC颗粒对液相线铸造铝舍金组织的影响。结果表明,当原位TiC颗粒达到2％时,舍金铸态组织基本变成等轴晶;二次加热后平均晶粒尺寸随着保温时间的延长具有长大现象,但是随着原位TiC颗粒的含量增加,长大幅度变小,颗粒抑制晶粒长大程度增强。     

TiC_p/7075 Al基复合材料二次加热中晶粒长大规律

采用原位反应近液相线铸造法制备4.4%TiCp/7075Al基复合材料,在600℃保温10～60 min,水淬固定其半固态组织,研究半固态二次加热过程中合金的晶粒长大规律,并与采用同样方法制备的7075基体合金进行对比分析。结果表明,4.4%TiCp/7075Al基复合材料的晶粒粗化速率常数为118.96μm3/s,远小于7075基体合金的晶粒粗化速率常数311.7μm3/s,晶粒长大速率明显减慢。分析其原因,由于原位TiC颗粒的生成,使得4.4%TiCp/7075Al基复合材料的晶粒长大激活能增加约50%,从而对二次加热过程中晶粒迅速长大的行为起到了显著的抑制作用。     

MICROSTRUCTURE AND PROPERTIES OF ZL201 ALLOY OBTAINED BY NEAR-LIQUIDUS ELECTROMAGNETIC CASTING

The microstructures of ZL201 alloy slurry prepared by near-liquidus electromagnetic casting （NLEMC）, electromagnetic casting（EMC）, and near-liquidus casting（NLC） were investigated by means of electron microscopy and image analysis. Mechanical properties of as-cast alloys were determined. The results show that the NLEMC induces a fine, uniform, and equiaxed grain structure with a mean equal-area-circle grain diameter of 32.8μm. The as-cast aUoy has a hardness of HV122.8 and a tensite strength of 368MPa. Both of them are betterthan those of the alloys prepared by EMC and by NLC. The mechanism of grain refinement in the NLEMC alloy slurry was discussed.     

EVOLUTION OF AS—CAST MICROSTRUCTURES OF 356 ALUMINIUM ALLOY CAST BY LIQUIDUS CASTING

A new method (liquidus casting) was used for 356 Al alloy semi-solid slurry making. The structures of 356 Al alloy cast by a Fe mould and semi-continuous casting machine at different temperatures were investigated. How the globular grains form was also discussed. The results show that either being cast by single Fe mould or semi-continuous machine, the micro structures are not conventional dendrites but fine and net-globular grains. The average gram size is smaller than 30?m and suitable enough for thixoforming, meanwhile it can improve the mechanical properties of following products. Under the suitable casting velocity and cooling intensity, most of global grains prolong their global growth and collide with each other before dendritic growth because of the large amount of the nucleation sites.     

Semi-solid extrusion of aluminum alloy ZL116

The semi-solid forward-extruding feasibility of reheated ZL116 alloy cast by the near-liquidus semicontinuous casting process was studied by analyzing the microstructures and properties of forward-extruded bars. The results show that the microstructure of the ZL116 alloy billets cast by near-liquidus semi-continuous casting is mainly made up of homogeneous, fine global- or rosette-shaped grains. The microstructure of the billets, reheated and held at 575℃, contains stable and net-spherical grains which are suitable for semi-solid thixoforming. The semi-solid forward-extruded bars of the ZL116 alloy billet are facially smooth, microstructurally fine and homogeneous. Therefore the feasibility of semi-solid forward-extrusion of ZL116 alloy is thus excellent.     

Microstructures of an AlSi7Mg alloy by near-liquidus casting

Semi-solid ingots of an AlSi7Mg alloy were obtained using the method of near liquidus casting. Their micro- structures exhibit the characteristics of fine, equiaxed, and non-dendrite, which are required for semi-solid forming. The in- fluences of casting temperature, heat preservation time, and cooling rate on the microstructure were also investigated. The results show that in the temperature region near liquidus the grain size becomes small with a decrease in casting temperature. Prolonging the heat preservation time makes grain crassitude at the same temperature. And increasing the cooling rate makes grain fine. The microstructure of the alloy cast with iron mould is finer than that with graphite mould.     

近液相线半连续铸造A356铝合金显微组织

采用近液相线半连续铸造法制备铸造A356铝合金，获得金属半固态加工要求的细小，等轴的“非枝晶”组织，研究了铸造温度、保温时间及冷却速度对该组织的影响规律。结果表明，在液相线附近，降低铸造温度，有利于减小晶粒尺寸；晶粒平均等积圆直径最小可达42．6μm，初始固相体积分数最多可达98．4％，同一温度下，晶粒尺寸随保温时间的延长而粗化；冷却速度快，晶粒尺寸细小；同一铸锭，其中心部位的组织比边缘部位的组织粗大，且分布均匀、等轴特征明显。     

不同铸造方法对7075铝合金热导率及力学性能的影响

采用金属型铸造、液态挤压铸造和半固态挤压铸造方法制备了7075铝合金,研究了不同铸造工艺对7075铝合金热导率与力学性能的影响。结果表明,金属型铸造晶粒粗大,产生枝晶偏析降低塑韧性,抗拉强度及伸长率最小,分别为121 MPa和2.78%,但晶粒粗大使热量传导路径宽,对电子散射几率小,电子的平均自由程较长,热导率相对较高,达到了139.67W/(m·K);液态挤压铸造晶粒细化,抗拉强度和伸长率分别为239MPa和5.75%,但晶粒细小且枝晶臂较多,对电子散射程度大,热导率最低,为120.94W/(m·K);半固态挤压铸造的晶粒致密细小且圆整,抗拉强度及伸长率最高分别达到248MPa和7.46%,且热导率为126.07W/(m·K)。     

Non-dendritic structural 7075 aluminum alloy byliquidus cast and its semi-solid compression behavior

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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.     

Semisolid continuous casting of AS41B magnesium alloy using inclined cooling plate

Abstract

One new casting topic is semisolid casting technology. It requires solid–liquid coexistence in slurry containing fine and globular crystals surrounded by liquid metal. The authors have made such the slurry using an inclined cooling plate and continuously cast AZ91 and AZ31 magnesium alloys. The factors that influence the best slurry with fine and globular crystals are the casting temperature and the length and inclination angle of the cooling plate. This investigation describes the best casting and cooling plate conditions to make semisolid slurry of AS41B magnesium alloy. The best conditions are then applied to produce continuous casting billets of AS41B magnesium alloy using an inclined cooling plate and a horizontal continuous casting machine. A 60 mm diameter AS41B billet was successfully obtained, and globular crystals (average size 57 μm) appear in the microstructures.     

Preparation of AZ91D magnesium alloy semi-solid billet by new strain induced melt activated method

1 Introduction AZ91D magnesium alloy has received more attention due to its high specific strength, specific rigidity and good dimensional stability and so on[1]. Thixoforming is one of the best methods with regard to forming AZ91D magnesium alloy compone…