喷射沉积连续挤压一步成形7075铝合金微观组织研究

采用喷射沉积连续挤压方法制备7075铝合金以消除元素偏析、组织粗大、第二相分布不均和缩孔、缩松等缺陷,并将其微观组织和元素分布情况与铸态合金进行比较。研究表明,喷射沉积连续挤压7075铝合金杂质元素含量低、组织细小、合金元素分布均匀。金相组织观察表明喷射沉积使沉积坯平均晶粒尺寸比铸态合金显著减小,并呈等轴晶形态。经过连续挤压后,基体致密度提高,第二相细化,沿挤压方向均匀分布。TEM组织观察表明,沉积坯在连续挤压过程中发生动态再结晶,平均再结晶晶粒尺寸为3～5μm。回归再时效处理后屈服强度和伸长率达到493 MPa和12.6%,分别超过AMS 4050H航空标准的9.6%和26%。EDS分析结果表明,喷射沉积连续挤压制备的7075合金主元素偏析得到很好抑制,杂质元素O、C的分布更加均匀,有利于合金综合性能提升。     

A Comprehensive Overview on the Latest Progress in the Additive Manufacturing of Metal Matrix Composites: Potential,Challenges, and Feasible Solutions

Nowadays, as an emerging technology, additive manufacturing(AM) has received numerous attentions from researchers around the world. The method comprises layer-by-layer manufacturing of products according to the 3D CAD models of the objects. Among other things, AM is capable of producing metal matrix composites(MMCs). Hence, plenty of works in the literature are dedicated to developing different types of MMCs through AM processes. Hence, this paper provides a comprehensive overview on the latest research that has been carried out on the development of the powder-based AM manufactured MMCs from a scientific and technological viewpoint, aimed at highlighting the opportunities and challenges of this innovative manufacturing process. For instance, it is documented that AM is not only able to resolve the reinforcement/matrix bonding issues usually faced with during conventional manufacturing of MMCs, but also it is capable of producing functionally graded composites and geometrically complex objects. Furthermore, it provides the opportunity for a uniform distribution of the reinforcing phase in the metallic matrix and is able to produce composites using refractory metals thanks to the local heat source employed in the method. Despite the aforementioned advantages, there are still some challenges needing more attention from the researchers. Rapid cooling nature of the process, significantly different coe fficient of expansion of the matrix and reinforcement, processability, and the lack of suitable parameters and standards for the production of defect-free AM MMCs seem to be among the most important issues to deal with in future works.     

热挤压对7055铝合金力学性能及组织的影响

采用挤压铸造成形工艺制备7055高强铝合金,研究了热挤压参数对合金力学性能及微观组织的影响,并与铸态下的力学性能及微观组织进行了对比.结果表明,热挤压态下的7055铝合金的微观组织和力学性能均优于铸态,并且晶粒随着比压的增加趋于细化,抗拉强度随着比压的增加趋于提高.当比压为75 MPa时,在730 ℃温度下进行挤压浇注,经过双级固溶处理和时效后,合金的晶粒明显细化,抗拉强度达到681.4 MPa,伸长率达到7.14%.     

不同轧制压下率铝/钢复合板界面及断裂分析

对液-固双辊铸轧法制备的铝/低碳钢复合板经450℃退火1.5 h后进行三道次轧制处理,每道次轧制处理后复合板压下率分别为25%、35%和45%。利用SEM和EDS观察界面组织并分析元素分布,通过原位拉伸试验观察复合板失效过程,测试其抗拉强度和伸长率。结果发现,退火态复合板界面处存在连续的扩散层,轧制态复合界面处扩散层在压力作用下破碎成块状,且压下率越大,扩散层厚度及其破碎的块状尺寸越小。25%和35%压下率复合板界面处存在明显裂纹及孔洞,45%压下率复合板界面处裂纹消失。退火态复合板A356铝合金侧主裂纹源于共晶Si颗粒和偏析共晶Si颗粒处,45%压下率复合板的主裂纹是由铝基体处的小裂纹迅速扩展而形成。45%压下率复合板具有最好的界面结合品质、良好的协调变形能力,抗拉强度达441 MPa,且伸长率为3.03%。     

挤压变形对Mg-5.5Zn-1.7Nd-0.7Cd-0.5Zr合金组织和性能的影响

采用光学显微镜及透射电镜研究了Mg-5.5Zn-1.7Nd-0.7Cd-0.5Zr镁合金在不同挤压变形条件下的组织和性能。结果表明,在一定的挤压条件下,当挤压温度降低或挤压比增大,晶粒变细小,合金的抗拉强度和屈服强度提高;在温度为340℃,挤压比为16时,合金抗拉强度为334MPa,屈服强度为300MPa,伸长率为13%,力学性能优良,平均晶粒直径为7μm。     

压射比压对流变挤压铸造7075合金组织及性能的影响

采用剪切低温浇注工艺（LSPSF）制备了半固态7075合金浆料,对流变挤压铸造成形铸件的组织和力学性能进行分析,研究了压射比压对7075合金组织及力学性能的影响。结果表明,随着压射比压从50 MPa增大到110 MPa,晶粒平均直径从39.3μm减小到31.6μm;铸件容易发生液相偏析固相率从82%减少到63%,液相偏析有增大倾向,抗拉强度增加,但伸长率先增加后减小;压射比压为80MPa左右时,能生产出综合性能良好的7075合金铸件。     

复合环缝式电磁搅拌对7075铝合金挤压铸造组织及性能的影响

开发了复合环缝式电磁搅拌（Multi-Annular Electromagnetic Stirring,M-AEMS）熔体处理方法,并研制了M-AEMS熔体处理装置。采用该装置对7075铝合金进行了熔体处理,并经挤压铸造直接成形。结果表明,经M-AEMS处理后挤压铸造成形的7075铝合金铸件的平均晶粒尺寸减小且均匀性均明显提高,宏观偏析也得到明显改善,经T6处理后,铸件的力学性能达到锻件水平。     

Effects of Sb Addition on Microstructural Evolution and Mechanical Properties of Mg–9Al–5Sn Alloy

The Mg–9Al–5Sn-xSb(x=0.0,0.3,0.6,1.0,1.5 wt%) alloys were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2. The effects of Sb additions on the microstructure and mechanical properties of the Mg–9 Al–5 Sn alloys were investigated by optical microscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer. The results indicated that the phases α-Mg matrix, Mg_2_Sn, Mg_3Sb_2 and Mg_17 Al_12 exist in the as-cast Sb-containing alloys. Sb addition results in the precipitation of Mg_3Sb_2. The dendritic size of these alloys decreases with the addition of Sb. Both their ultimate tensile strength and yield strength of extruded alloys increase, and their elongation decreases gradually with increasing the content of Sb. The better mechanical properties of the as-extruded alloys were achieved due to the refined grains and the formation of dispersive second phases Mg_3Sb_2.     

挤压变形对粉末冶金Al-Si-Cu合金组织和性能影响

利用金相观察、SEM和XRD等方法研究了生坯挤压并在N2气氛下烧结制备的Al-Si-Cu合金的微观组织,并测试了其力学性能。结果表明,Al-Si-Cu合金生坯经过挤压后,致密度增加,Si和Cu的晶粒均匀分布在Al基体中,无明显界面。其物相组成为α-Al、β-Si、Al2O3、CuAl2和Cu4Si,其中CuAl2和Cu4Si是在挤压后烧结过程中形成。合金力学性能显著提高,其硬度（HV）、抗拉强度和伸长率分别为71.5、400 MPa和13.8%,断口形貌从典型的冰糖状脆性断口转变为含有韧窝的塑性断口。     

AZ61镁合金在不同挤压温度下的组织与力学性能

对变形镁合金AZ61铸态试样和不同温度下的挤压成形试样的微观组织结构、室温力学性能以及拉伸断口进行了研究。结果表明,360℃的热挤压温度不能成形试样,在370、385、400℃下进行热挤压可以得到外形完整、表面光洁的试样;随着挤压温度提高,AZ61挤压试样发生再结晶的晶粒数量显著增加,达到400℃时形成均匀细小的等轴晶组织;370、385、400℃下的挤压试样断口均表现为明显的塑性断裂特征,400℃时挤压试样的抗拉强度达到297.43MPa,屈服强度达到221.42MPa,伸长率为22.39%,具有较好的力学性能。     

EW75-0.7Al合金挤压、时效态的组织及力学性能

通过OM、SEM、硬度及拉伸等测试手段,研究了EW75-0.7Al合金挤压及时效态的组织和力学性能。结果表明,挤压后合金晶粒明显细化,室温力学性能显著提高,抗拉强度为330MPa,屈服强度为242MPa,伸长率为11%。通过对合金进行T5时效处理,确定EW75-0.7Al合金的最佳T5峰时效制度为225℃×12h,经过T5峰时效处理后,合金的室温强度相比挤压态提高约100MPa。T5峰时效态合金在200℃高温下,力学性能下降不明显,在250℃高温下力学性能显著降低。通过分析合金高温下的断裂方式,发现250℃高温下,EW75-0.7Al合金的晶界强度显著降低,且时效析出相与基体的结合能力下降,最终导致合金在该温度下力学性能明显降低。     

稀土对AZ61镁合金变形过程中组织与性能的影响

研究了不同的稀土含量（富Ce和Mg-Nd中间合金）对AZ61镁合金在热挤压变形过程中显微组织和力学性能的影响。结果表明,在加入1%～4%的混合稀土后,铸态AZ61镁合金组织中的β相明显减少,铸态组织晶粒得到细化,大部分的Ce,Nd与Al结合生成高熔点、高稳定性的稀土相Al4Ce或者Al4Ce和Al3Nd稀土混合相,并呈针状、棒状或者不规则块状分布于晶界或晶粒内部,同时各试验合金中均不同程度分布有不规则的块状α-Al8Mn5相;在热挤压过程中,Al4Ce或者Al4Ce和Al3Nd稀土混合相阻碍晶粒或亚晶粒长大,使晶粒较铸态组织变细,合金力学性能随稀土含量的增加有所提升,但由于稀土相较粗大,割裂晶界及晶粒间的结合力,使其性能大幅度下降;铸态AZ61+xRE各试验合金均为脆性断裂机制,挤压态AZ61合金断裂方式属于以韧性为主的韧脆混合断裂,含稀土挤压态合金中分布有塑性特征的韧窝,但主要以解理断裂为主。     

Effect of Extrusion Temperature on the Microstructure and Mechanical Properties of Mg–5Al–2Ca Alloy

In this work, the Mg–5Al–2Ca alloy was extruded at 573, 623 and 673 K, with a ratio of 16:1 and a constant speed of 3 mm/s. Results demonstrate that the Al2Ca particle is formed in Mg–5Al–2Ca alloy. The size, amount and distribution of Al2Ca particles are influenced evidently by extrusion temperature. Unlike previous reports, the intensity of basal texture increases with increasing extrusion temperature, and the reasons are analyzed and given. Even though the average grain size increases as the extrusion temperature increased from 573 to 623 K, the YS, UTS and elongation of asextruded Mg–5Al–2Ca alloy are almost kept the same at 573 and 623 K. The reason is speculated as the balance of grain size, Al2Ca phase and texture at the two temperatures. The work hardening rate depends on extrusion temperature, and the largest θ value of Mg–5Al–2Ca alloy is obtained when the extrusion was performed at 623 K.     

Investigation on microstructure and mechanical properties of diffusion bonded Al/Mg2Si metal matrix composite using copper interlayer

Diffusion bonding of Al/Mg₂Si metal matrix composite (MMC) using Cu interlayer at optimal bonding temperature of 540 °C for various bonding durations was investigated. This metal matrix composite (MMC) containing 15% Mg₂Si particles was produced by in situ technique. Specific diffusion bonding process was introduced as a low vacuum technique. The composition and microstructure of the joined areas were examined by X-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDS). Microhardness and shear tests were conducted to the samples to evaluate the effect of bonding duration on weldability. Several different diffusion layers exist at the bond region depending on the bonding duration. The shear strength of joints increased with bonding duration due to elimination of CuAl₂ brittle diffusion layer.     

Characterization of the High-Strength Mg–3Nd–0.5Zn Alloy Prepared by Thermomechanical Processing

Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications.Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg–3 Nd–0.5 Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400 °C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall–Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall–Petch of extruded Mg–3Nd–0.5 Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall–Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg–3Nd–0.5 Zn alloys.