Development of aluminum rheo-extrusion process using semi-solid slurry at low solid fraction

An aluminum extrusion process is mainly used to fabricate long tubes, beams and rods for various applications. However, this process has a high production cost due to the need for investment of high-pressure machinery. The objective of this work is to develop a new semi-solid extrusion process using semi-solid slurry at low solid fractions. A laboratory extrusion system was used to fabricate aluminum rods with the diameter of 12 mm. The semi-solid metal process used in this study was the gas induced semi-solid (GISS) technique. To study the feasibility of the GISS extrusion process, the effects of extrusion parameters such as plunger speed and solid fraction on the extrudability, microstructure, and mechanical properties of extruded samples were investigated. The results show that the plunger speed and solid fraction of the semi-solid metal need to be carefully controlled to produce complete extruded parts.     

Evolution of microstructure in semi-solid slurries of rheocast aluminum alloy

Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in semi-solid slurries for the control of the rheological behavior in semi-solid state. An experimental apparatus was developed which can capture the grain structure at different times at early stages to understand how the semi-solid structure evolves. In this technique, semi-solid slurry was produced by injecting fine gas bubbles into the melt through a graphite diffuser during solidification. Then, a copper quenching mold was used to draw some semi-solid slurry into a thin channel. The semi-solid slurry was then rapidly frozen in the channel giving the microstructure of the slurry at the desired time. Samples of semi-solid 356 aluminum alloy were taken at different gas injection times of 1, 5, 10, 15, 20, 30, 35, 40, and 45 s. Analysis of the microstructure suggests that the fragmentation by remelting mechanism should be responsible for the formation of globular structure in this rheocasting process.     

铝合金半固态压铸工艺参数及性能研究

应用具有不同厚度的简单板材模具来系统研究压铸工艺参数对A356铝合金半固态压铸件性能的影响,以优化半固态压铸工艺及其参数.试验结果表明,对A356铝合金半固态压铸,其性能随压射压力的增大而提高,当压射压力大于100 MPa,则性能基本上不再提高.压铸速度过小或过大会降低压铸件的性能.另外建压时间、坯料加热温度、模具预热温度以及脱模剂等参数对半固态压铸件性能也有明显的影响.     

半固态流变模锻工艺参数对铝合金制件质量的影响

分析半固态流变模锻技术的工艺过程及其特点,指出影响铝合金性能的工艺参数主要有：浇注温度、模锻比压、模锻速度、保压时间、模具温度。根据有关试验结果,归纳出采用半固态流变模锻工艺生产的铝合金可能出现的缺陷有：裂纹、冷隔、型腔充填不满、皮下针孔、疏松、缩孔、气孔。针对这些缺陷提出了相应的预防措施。     

压铸ADC12铝合金基座的开裂机制分析

利用扫描电镜、金相显微镜、电感耦合等离子发射光谱仪等手段,对压铸ADC12铝合金云台基座开裂失效进行组织及成分分析,并借助弹塑性有限元法分析了云台基座在使用过程中采取急停等操作后的应力分布情况。结果表明,ADC12铝合金在铸造过程中产生大量的缩孔、偏析等缺陷,特别是在弯角部位,存在偏析瘤。这些缺陷,导致合金的力学性能严重下降。此外,在基座底部前后端与高台的交界处存在应力集中。因此,导致压铸ADC12铝合金云台基座的开裂失效。     

Rheo-squeeze casting of semi-solid A356 aluminum alloy slurry

The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630-650 °C, the slurry with spherical primary α(Al) grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α(Al) grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α(Al) grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 155 °C for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300-320 MPa, the yield strength 230-255 MPa, and the elongation 11%-15%.     

半固态合金流变成形技术的研究现状与发展

系统总结了半固态合金流变成形技术的研究进展和工业应用现状.按照半固态浆料的制备方法及制浆与成形之间的关系,分别介绍了机械搅拌式流变铸造、电磁搅拌式流变射铸、倾斜板浇注式流变铸造、液相线铸造(模锻)和Semi-Solid Rheocasting(SSRTM)技术的成形原理、技术特点、设备结构和工业应用现状,分析了其发展前景.     

AlSi7Mg轮毂半固态流变挤压铸造成形数值模拟

利用半固态流变挤压铸造技术代替传统铸造来生产汽车轮毂。基于有限元软件AnyCasting和carreau表观粘度模型,对铝合金轮毂的半固态流变挤压铸造成形过程进行了数值模拟,研究了压射速度、浇注温度和模具预热温度3个主要工艺参数对半固态浆料充型和凝固过程的影响规律,并采用正交试验设计获取了最佳的工艺参数。结果表明,最佳的工艺参数组合为压射速度0.07 m/s、浇注温度595℃和模具预热温度225℃,同时得出半固态浆料的浇注温度对铸件缺陷的影响最大,压射速度其次,模具预热温度最小。     

复杂零件半固态压铸充型过程的计算机仿真

使用二次开发的ANSYS有限元软件，对铝合金半固态压铸复杂件的充型与模具内浇道形貌之间关系进行详细的计算机仿真。首先对仿真模型进行了合理的简化处理，然后分别模拟和分析了压铸速度及浆料粘度等主要工艺参数对压铸件质量的影响，进而对半固态模具的内浇道进行改进。X射线探伤证实，铝合金半固态压铸造模具的内浇道是影响其性能的关键因素，同时也表明，文中提出的简化仿真模型可以较好地仿真铝合金复杂件半固态压铸造过程。     

半固态A356压铸件充型与凝固过程的数值模拟

利用ProCAST软件对A356合金半固态压铸件下壳体进行耦合数值模拟。结果表明,在模具温度为220℃,充型温度为590℃、压射速度为5m/s时,半固态浆料充型平稳,温度场分布均匀,减少了缩孔、缩松等缺陷,为A356合金半固态压铸成形工艺的制定和优化提供了依据。采用此工艺参数,生产出合格铸件。在该件上所需部位可以钻螺纹孔,与其他零件装配使用。通过试验,验证了数值模拟优化工艺参数的合理性。     

半固态金属浆料制备技术的研究进展

总结了30余年来半固态金属浆料制备技术的研究和应用现状,分别介绍了压室浆料制备技术、单螺旋机械搅拌浆料制备技术、双螺旋机械搅拌浆料制备技术、低过热度倾斜板浇注浆料制备技术、低过热度浇注和弱机械搅拌浆料制备技术、连续流变转换浆料制备技术、低过热度浇注和弱电磁搅拌浆料制备技术、蛇形通道浇注浆料制备技术、熔体分散混合浆料制备技术、转桶搅拌浆料制备技术、波浪倾斜板浇注浆料制备技术、旋转倾斜圆筒浆料制备技术、超声振动浆料制备技术、熔体处理和双向电磁搅拌浆料制备技术、低于液相线温度浆料制备技术、偏旋热焓平衡浆料制备技术、气泡搅拌浆料制备技术及其发展前景。     

原位Mg_2Si/AM60镁基复合材料半固态流变压铸成形研究

采用原位合成法制备了Mg_2Si/AM60镁基复合材料,观察了Mg_2Si颗粒的分布情况,并对其半固态流变压铸成形进行了研究.结果表明,Mg_2Si颗粒呈汉字状分布;半固态成形减轻了传统压铸件缩孔、偏析等铸造缺陷;液态压铸微观组织基本形貌以大块枝晶为主.液相不规则分布在枝晶间;半固态流变压铸后微观组织绝大部分为球状或类球状组织.     

Effects of temperature and time on three-dimensional microstructural evolution of semi-solid 2A14 aluminum alloy during short process preparation of semi-solid billets

To shorten the preparation process of semi-solid billets, semi-solid billets of 2A14 aluminum alloy were prepared by wrought aluminum directly semi-solid isothermal treatment (WADSSIT) process. Three-dimension (3D) combined microstructure evolution, namely transverse direction (TD) surface, rolling direction (RD) surface, and normal direction (ND) surface, was studied. Effects of temperature and holding time on average grain size and average shape factor were investigated. The results showed that the optimum conditions for preparation of 2A14 semi-solid billets by this process were 615 °C and 20 min (average grain size of 124 μm and shape factor of 0.81). Electron backscatter diffraction (EBSD) observations indicated that the microstructure was completely recrystallized when it was heated to 600 °C. Grain size was increased with the increase of temperature and grew up slowly with the holding time prolonging. Roundness was increased with increase of holding time but was not sensitive to temperature.     

流变压铸成形镁合金AZ91D的显微组织与性能

采用双螺杆机械搅拌法制备半固态镁合金浆料,对比研究了液态压铸与半固态流变压铸成形镁合金AZ91D的组织与性能,探讨了半固态成形镁合金铸件的热处理强化机制.试验结果表明,流变压铸成形铸件与液态压铸成形铸件在铸态时的力学性能相当;由于半固态成形减轻了铸件内部气孔、偏析等铸造缺陷,因而T4和T6热处理均明显地提高了半固态成形镁合金铸件的力学性能.研究还得出,液态压铸成形镁合金铸件经过固溶处理之后,其抗拉强度和伸长率也有所提高,但是,时效处理明显地恶化了铸件的力学性能.     

Impact strength and structural refinement of A380 aluminum alloy produced through gas-induced semi-solid process and Sr addition

Semi-solid processing of A380 aluminum alloy was performed by gas induced semi-solid (GISS) process. The effects of argon inert gas flow rate, starting temperature and duration of gas purging as key GISS parameters and also modification with Sr on the structural refinements, hardness and impact strength of GISS alloys were investigated. Microstructural evolution shows that there is an important effect of the pouring temperature and Sr addition on the morphology and size of primary α(A1) in the alloy to change from coarse dendritic to fine globular structure. The best sample which has fine grains of 51.18 μm in average size and a high level of globularity of 0.89 is achieved from a GISS processing of Sr modified alloy in which the gas purging started at 610 °C. The impact strength of the GISS optimized samples ((4.67±0.18) J/cm²) shows an increase of about 40% with respect to the as-cast sample due to the globular structure and fibrous Si morphology. Moreover, the hardness of the optimized GISS sample ((89.34±2.85) HB) increases to (93.84±3.14) HB by modification with the Sr and GISS process. The fracture surface of Sr modified alloy is also dominated by complex topography showing typical ductile fracture features.     

倾斜冷却法浆料制备研究现状

介绍了倾斜冷却法制备半固态合金浆料的实验装置、实验方法,以及采用这些实验装置所进行的研究内容,简述了倾斜板法在半固态连铸、半固态挤压、半固态轧制、半固态压铸和半固态锻造中的工业应用研究现状,提出了倾斜冷却法制备浆料的发展前景。     

Effects of processing parameters on microstructure of semi-solid magnesium alloy

In this paper, the effects of pouring temperature of magnesium melt, preheating temperature of the barrel of the screw mixer, and shear rate on the solidified microstructures of semi-solid slurry were investigated by a mechanical stirring semi-solid process. The appropriate processing parameters of slurry preparation were obtained, and the mold filling ability of semi-solid slurry for thin-walled casting was examined. Results indicate that the solid volume fraction of non-dendritic microstructure increases with a decrease in pouring temperature of magnesium melt and the barrel preheating temperature of the screw mixer. Also the grain size of primary α-phase is reduced. Furthermore, the solid volume fraction of semi-solid nondendritic structure decreases with an increase of shear rate. The fine and round granular microstructure with 30～50 μm in size of semi-solid AZ91D magnesium alloy was presented. Finally, a 1.0 mm thin-walled casting with a clear contour and good soundness was successfully made by semi-solid rheo-diecasting.     

充填速度与浇口对半固态AlSi7Mg合金成形过程的影响

确定半固态触变成形的边界条件,在半固态表观粘度耦合于流场的动量方程上,建立半固态AlSi7Mg充型过程的计算模型.对不同充填速度、浇口形状以及浇口设置位置下半固态成形过程进行模拟分析.结果表明:半固态合金的充填速度对流态及成形质量具有明显影响,与压铸相比,半固态浇口形状、设置位置等因素对充填流态影响相对较小,所以半固态工艺设计较为灵活.半固态压铸机的充填流量及充填压力取决于浇口面积、充填速度以及合金种类.充填速度决定半固态浆料流动形态,进而影响半固态制件的成形质量.     

半固态A356合金微观组织特征对充型能力的影响

采用电磁搅拌法制备了具有不同微观组织特征的半固态A356合金浆料,用图像分析软件对浇注前浆料金相试样的初生相微观组织特征进行了测定,利用间接挤压铸造方法铸造阿基米德螺旋线试样,以挤压成形后的螺旋线试样长度衡量充型能力,通过多元回归,建立了半固态A356合金初生相微观组织特征与充型长度之间的数学表达式。结果表明:半固态浆料充型能力不仅与初生相微观组织特征参数有关,微观组织特征参数的交互作用对充型能力的影响也较大。利用该表达式可以对半固态浆料充型能力进行预测,进而指导半固态浆料制备参数设计、间接挤压铸造工艺设计和缺陷预测。     

Microstructure characteristics and mechanical properties of rheoformed wrought aluminum alloy 2024

The microstructure characteristics and mechanical properties of 2024 wrought aluminum alloy produced by a new rheoforming technique under as-cast and optimized heat treatment conditions were investigated. The present rheoforming combined the independently developed rheocasting process, named as LSPSF (low superheat pouring with a shear field) process, and the existing squeeze casting process. The experimental results show that LSPSF can be used to prepare sound semi-solid slurry within 25s to fully meet the production rate of squeeze casting. The primary α (Al) presents in mean equivalent diameter of 69μm and shape factor of 0.76, and features zero-entrapped eutectics. Compared with conventional squeeze casting, the present LSPSF rheoforming can improve the microstructures and mechanical properties. An optimized heat treatment results in substantial reduction of microsegregation and significant improvement of mechanical properties, such as yield strength of 321MPa, ultimate tensile strength of 428MPa and elongation of 12%.