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…     

镁合金ZK60-RE半固态坯的微观组织演变

采用常规铸造法和等径道角挤压分别制备了镁合金ZK60-RE半固态坯;用金相显微镜研究了2种半固态坯料在等温热处理过程中的微观组织演变。结果表明：与传统铸造方法制备的半固态坯相比,采用等径道角挤压制备的半固态坯的晶粒细小、圆整,适合于半固态成形。在等温热处理过程中,2种坯料晶粒粗化的机制是合并长大和Ostwald长大。铸态坯料晶粒液相来源于非平衡凝固时在晶内产生的共晶组织,以及在随后的合并长大过程中晶粒所包裹的液相。随着保温时间的延长,铸态坯料的晶粒尺寸变化情况是：增大、减小然后又增大;而挤压态坯料的晶粒尺寸呈单一增大趋势。     

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.     

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…     

Mg-Al系镁合金半固态坯料制备及触变挤压研究

采用拉伸试验机、金相显微镜和等径道角挤压等试验方法对Mg-Al系镁合金半固态坯料制备及触变挤压过程进行了研究.结果表明,等径道角挤压工艺对Mg-Al系镁合金有很好的应变诱导效果.经过等径道角挤压的Mg-Al系镁合金力学性能高,晶粒细小.等径道角挤压+等温处理方法制备的Mg-Al系镁合金半固态坯的微观组织晶粒细小,球化程度高,微观组织非常均匀.生产的AZ61、AZ80、AZ91D和AM60镁合金角框零件的微观组织细小,抗拉强度分别达到306.8、308.3、299.8、321.6MPa.伸长率分别达到21.6%、28.4%、14.6%和29.6%.     

等温处理对挤压态AZ80A镁合金半固态组织的影响

采用应变诱发熔化激活法(SIMA)工艺制备了AZ80A镁合金半固态坯料,研究了保温温度和保温时间对半固态组织的影响。结果表明:随着保温温度的升高和保温时间的增加,AZ80A镁合金的平均晶粒尺寸与液相率都呈上升趋势,形状因子呈先增大后减小的趋势。半固态组织由α-Mg晶粒、Al、Zn元素富集形成的晶界处液相和晶内“小液池”组成,其组织演变分为初始晶粒合并长大,晶粒球化、彼此分离,最终合并粗化3个阶段。采用该种方法制备AZ80A镁合金半固态坯料时合适的保温温度为550 ℃、保温时间为45 min,此时半固态组织的平均晶粒尺寸、形状因子和液相率分别为89 μm、0.795和26.7%。     

变形程度对7A04合金半固态触变组织的影响

获得具有触变特性的均匀的、近球形的显微组织是半固态触变成形工艺的基础和关键。以挤压态7A04合金SIMA法生成触变组织为例．研究变形程度对其半固态触变组织的影响。结果表明：在加热前的变形程度对显微组织的影响很大，随着变形程度的增加，晶粒尺寸减小，晶粒形状越趋于球形；当变形程度超过0．3时，晶粒尺寸及其球形化速度逐渐减慢并趋于稳定值。此外，经过冷变形后，晶粒内及晶粒间的偏析减小，晶界易被低熔点液相浸润．更易获得均匀的、近球形的触变组织。     

挤压速度和电磁铸造锭坯对AZ31镁合金板材组织和性能影响

文章研究挤压条件下挤压速度和电磁铸造锭坯对挤压态AZ31镁合金板材组织和性能的影响。研究结果发现,挤压速度比较低时,板材晶粒尺寸小,板材的表面质量比较好;随着挤压速度的降低,抗拉强度、屈服强度和延伸率都有一定的提高。由于镁合金是HCP的晶体结构,同时对挤压速度非常敏感,对变形均匀性影响比较大,因此造成挤压板材的内外晶粒大小不均。在电磁场的作用下,溶质在晶内的固溶度增大,同时晶粒大小也比常规铸造的细小,因此电磁铸造的锭坯经挤压机挤压后,挤压板材的晶粒尺寸比较细小,且强度和塑性都有所提高。     

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.     

A356铝合金半固态成形坯料二次加热工艺的优化

使用多工位电磁感应旋转加热装置对A356圆棒料进行重熔加热。选用不同的加热功率和工位,得到不同的非树枝晶组织,借助晶粒参数(如晶粒平均大小、形状系数、固相率等)对得到的显微组织进行研究,选出综合指标最优的加热工艺,再对该工艺加热的坯料压铸成阶梯试样。通过对阶梯试样性能分析,验证了该工艺的合理性和优越性。结合凝固理论,分析了坯料二次加热的演变规律。     

铝含量对应变诱发法半固态镁合金的影响

结合半固态合金成分设计原则,通过热力学计算,研究了3种成分的半固态镁合金。通过组织观察和流变学参数分析表明,半固态组织的形成速度随铝含量增加而加快,固相粒子变得细小、圆整。分析得出铝元素主要通过两个方面影响半固态组织,一个是液相形核,另一个是再结晶晶粒尺寸。随着铝含量增加,液相形核数量增多,再结晶晶粒尺寸减小,这些都促进了半固态组织的形成和演变,有利于镁合金半固态加工。     

6061铝合金半固态坯料二次加热工艺及组织演变

针对近液相线半连续铸造技术制备的6061铝合金半固态坯料,在不同加热温度及保温时间下进行二次加热,采用光学显微镜及图像分析仪考察试样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的液相形成、组织演变及晶粒长大过程。结果表明,二次加热温度及保温时间共同影响着微观组织演变过程,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。有效地控制二次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组织。     

Structural evolution of LC_4 alloy in making thixotropic billet by SIMA method

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触变模锻成形工艺对镁合金成形件力学性能的影响

采用半固态等温热处理法、近液相线模锻法和等通道角挤压法制备AZ91D—Y镁合金半固态坯料。分别将3种状态的坯料加热到半固态温度区间进行二次重熔后,进行了触变模锻成形。结果表明,在半固态温度为560℃,模锻压力为200MPa的条件下,半固态等温热处理法、近液相线模锻法和等通道角挤压法制备坯料分别保温30,20,15min后触变模锻获得最佳力学性能;随着坯料加热温度的升高,触变模锻成形件力学性能呈现先上升后下降的趋势;增加成形压力有利于触变模锻成形件力学性能的提高;在相同成形条件下,等通道角挤压法制备坯料触变模锻后的力学性能最好,近液相线模锻法次之,半固态等温热处理法较差。     

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。     

Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting

Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like α-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, α-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in cavity, microstructural segregation of unmelted α-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.     

低频电磁场对半连续铸造Al-Mg-Si-Cu合金显微组织的影响

采用低频电磁场半连续铸造工艺制备Al-Mg-Si-Cu铝合金铸锭,研究了低频电磁场对Al-Mg-Si-Cu铝合金铸锭组织的影响。结果表明,施加低频电磁场可以细化Al-Mg-Si-Cu铝合金铸锭的晶粒组织,减轻晶内元素的偏析程度。与常规半连续铸造相比,施加频率为20 Hz、电流为120 A的交变电磁场后,铸锭中的等轴晶组织增多,枝晶状组织减少,晶粒尺寸变得更加细小,铸锭边部和中心平均晶粒尺寸由常规半连续铸造的170和259μm分别降至133和187μm,同时有利于提高溶质元素在晶内的分布,很大程度上减轻了溶质元素的偏析。此外,低频电磁场的电磁振荡使得液穴内部温度场和流动场更趋均匀,溶质元素分配系数增大,结晶区间变小,抑制了树枝晶的生长,促进了Al-Mg-Si-Cu合金半连续铸锭中非枝晶组织的形成和溶质元素的强制固溶,并且抑制了溶质元素的偏析。     

半固态5083铝合金的二次加热组织与触变轧制

采用大挤压比热挤压预变形的SIMA法制备了5083铝合金半固态坯料,研究了在不同加热温度和保温时间条件下二次加热重熔组织的演变规律,以及不同工艺参数对一道次触变轧制后带材力学性能的影响.结果表明,在二次加热过程中,晶粒形状和液相率主要受加热温度影响,而受加热保温时间的影响不大.在一道次触变轧制中,当二次加热温度为600℃,轧制变形量为60％时,可以获得抗拉强度为260.93MPa,伸长率为26.81％的较好综合力学性能的带材.经40％变形量二次冷轧后,带材的抗拉强度提高了70MPa.结合拉伸断口的宏观和微观形貌分析,可知带材的断裂方式为微孔聚集型的韧性断裂.     

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.     

Reheating and thixoforging of ZK60+RE alloy deformed by ECAE

The two-pass equal channel angular extrusion (ECAE) process was introduced into strain-induced melt activation (SIMA) to predeform a ZK60 alloy with rare earth (RE) addition. Microstructure evolution of ECAE-formed ZK60+RE alloy during reheating was investigated. Furthermore, tensile properties of thixoforged components were determined. The results show that the SIMA process can produce ideal microstructures, and spheroidized solid particles with little entrapped liquid can be obtained. With prolonging hold...