Microstructure characteristics and thermodynamic properties of A357-SiCp/A357 layered composites prepared by semi-solid vacuum stirring suction casting

A357-SiCp/A357 layered composites were prepared using a semi-solid vacuum stirring suction casting method.The microstructures,mechanical properties,and thermal conductivities of the composites fabricated under different suction casting processes were compared.Additionally,the microstructural evolution characteristics and performance enhancement mechanism of the A357-SiCp/A357 layered composites were discussed.The results demonstrate that suction casting at 610°C with a low solid phase ratio can significantly enhance the material density and reduce the agglomeration of SiCp.The A357-SiC_(p)/A357 interface is clear and straight with good bonding.With an increase in the suction casting temperature,the bending resistance and thermal conductivity of the A357-SiC_(p)/A357 layered composites exhibit a trend of significantly increase at first and then slowly decrease owing to casting defects,interface bonding,and SiCp distribution.Compared with SiCp/A357 composites,the bending strength,deflection,and thermal conductivity of the A357-SiCp/A357 layered composites increase from 257 MPa,1.07 mm,and 155.72 W·(m·K)^(-1) to 298 MPa,2.1 mm,and 169.86 W·(m·K)^(-1),respectively.This study provides a reference for improving the rheological casting of aluminum matrix layered composites.

New method of direct chill casting of Al-6Si-3Cu-Mg semisolid billet by annulus electromagnetic stirring

The electromagnetic direct chill （EMDC） casting process is a welt-established production route for aluminum alloy ingot, however, the skin effect restricts the casting diameter. In order to avoid this problem, annulus electromagnetic direct chill （A-EMDC） casting process has been developed. A three-dimension finite element computational model of A-EMDC casting process was established by using ANSYS Magnetic-Nodal programs and FLOTRAN CFD programs. Microstruetures of A-EMDC casting semi-solid Al-6Si-3Cu-Mg alloy billets were investigated. Two pairs of vortexes occur within the crystallizer with opposite direction in A-EMDC. The annulus gap is advantageous to increasing circulate flow, reducing the temperature gradient as well as shallowing liquid sump depth. The microstructure obtained by A-EMDC is globular or rosette-like, and the microstructure is homogeneous in the billet.

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 ℃, 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 ℃ for 5 h and then aged at 155 ℃ 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%.

Effects of casting speed on microstructure and segregation of electromagnetically stirred Aluminum alloy in continuous casting process

Recently, a semi-solid metal processing has been acknowledged as a cost-effective technique to be able to manufacture high quality product for the transportation industry. In this study a hypo-eutectic Al alloy was fabricated by means of an electromagnetic stirrer in continuous casting process and the microstructural change during solidification due to a fluid flow by electromagnetic stirring was examined. Due to the forced fluid flow during solidification a dendritic phase of primary α phase of Al alloy was turned into a globular phase, which can make the Al alloy get a thixotropic behavior in the semi-solid region. In order to establish the quantitative relationship between microstructure and the process parameters, the morphology shape, a silicon distribution and a size of primary α phase were observed according to casting speed in continuous casting machine. The primary α phase was turned into the degenerate dendrites approaching a spherical configuration with increasing casting speed. The fine-grained and equiaxed microstructure appeared at higher casting speed. A segregation behavior of Si element was declined with increasing casting speed and a very uniform distribution of Si element was observed on the billet at a casting speed of 600 mm·min-1. A thickness of the solidifying shell of the billet was shortened with increasing the casting speed.

SPHERICAL MICROSTRUCTURE FORMATION OF THE SEMI-SOLID HIGH CHROMIUM CAST IRON Cr20Mo2

The nondendritic semi-solid slurry preparation of high chromium cast iron Cr20Mo2 has been studied in this paper. The experiments show that the proeutectic austenitic particles are more spherical under a larger stirring power condition, even if the stirring time is shorter, while the proeutectic austenitic particles are not very much spherical under a smaller stirring power condition and some proeutectic austenitic dendrites also exist, even if the stirring time is very long. The experiments also show that when stirred for 5-6 minutes under the test condition, the semi-solid slurry with 40vol.%-50vol.% solid fraction and spherical proeutectic austenite in the size of 50-80μm can be obtained.

The Spatial and Temporal Evolution Behavior of Fluid Flow in Round Strands Continuous Casting Under Intermittently Reversing Direction Electromagnetic Stirring

Liquid metal flow behavior in round strands continuous casting under intermittently reversing direction electromagnetic stirring was measured by ultrasonic Doppler velocity-meter in a physical simulation system in order to investigate the effects of time interval(t_i)of periodically reversed magnetic field on the spatial and temporal flow.The results show that under electromagnetic stirring with direction reserved magnetic field,there's a periodically change of the metal flow velocity and rotation direction with the periodically direction changing of the magnetic field.From both the experimental and mathematical model calculation results,it is found that when t_i is nearly equal to the time required for the metal flow speeding to the maximum velocity from still and decreases to zero again,there is a critical value of the rate of dynamic pressure,which means the wash effect of the liquid metal flow.On this point,rate of dynamic pressure was proposed to be a criterion for optimization the processing of electromagnetic stirring.

液态搅拌铸造SiC_P及SiO_(2(P))增强Al-4wt%Mg基复合材料的界面反应研究

利用分析透射电镜研究了液态搅拌铸造原始态与氧化态ＳｉＣＰ以及ＳｉＯ２（Ｐ）增强Ａｌ－４ｗｔ％Ｍｇ基复合材料的界面反应情况。结果在原始态和氧化态碳化硅颗粒表面观察到细小的ＭｇＯ，石英粒子在高温下与基体中的镁反应生成ＭｇＡｌ２Ｏ４，并运用扩散理论分别解释了其反应机制。

电磁搅拌对液态金属运动及凝固组织的影响

旋转型电磁搅拌在钢的连续铸造、铸件成形与凝固、半固态浆料制备、液态金属电磁净化等工艺过程中的应用受到了材料工作者的高度重视,并不断地取得了电磁搅拌应用技术开发与理论研究的成果。分析了旋转型电磁搅拌作用下液态金属运动特点及电磁力计算,建立了液态金属旋转运动的数学模型,并得到周向速度分布的表达式,研究了旋转型电磁搅拌对连铸坯凝固组织的影响,为在旋转型电磁搅拌应用中工艺参数的优化提供了依据。

液态搅拌铸造SiC_p/ZL101复合材料研究

利用改进的机械搅拌法在液态下将氧化态SiC_p分散进ZL101合金液中,制备了SiC_p/ZL101复合材料。对该复合材料的复合工艺、组织和常规力学性能进行了研究。结果表明,SiC_p/ZL101复合材料中SiC_p分布均匀,与基体结合良好,SiC_p与基体界面上存在Mg和Si的富集。与基体合金相比,SiC_p/ZL101的硬度、抗拉强度和耐磨性,尤其是重载下的耐磨性显著提高,塑性虽然降低,但通过优化工艺可以使之降低得最少。

电磁搅拌对连铸结晶器内钢液流动的影响

为了研究电磁搅拌对连铸结晶器内钢液流动的作用效果,利用有限元数值模拟方法研究并探讨了不同电流频率、电流强度作用下的奥氏体不锈钢S30432小方坯连铸结晶器内磁感应强度、电磁力、流场以及流速的分布和变化情况。研究结果表明:电磁场的主要作用范围集中在电磁搅拌器内部区域,磁感应强度和电磁力随着电流强度的增加而增大,随着电流频率的增加先增大后减小,磁感应强度和电磁力的最大值分别出现在铸坯表面和近表面靠近磁轭的位置;电磁搅拌能够显著增强结晶器内钢液的纵向回流效果,有利于促进夹杂物浮回钢液表面,便于除气除渣净化钢液;电磁搅拌作用的施加,能够降低水口流入钢液的冲击深度,增强钢液在水平方向的流动,扩大钢液高流速区域,有利于钢液内部及表面的换热,从而,提高晶粒细化效果。

电磁搅拌作用下电流强度对结晶器内液面波动的影响

以某钢厂准ф250 mm连铸圆坯结晶器电磁搅拌为研究对象,采用电磁—流体单相耦合的方式及流体体积函数VOF模型,建立描述结晶器电磁搅拌作用下液面波动的数学模型,研究电磁搅拌作用下电流对液面波动的影响。结果表明,,随着电磁搅拌强度增强,液面波动变得剧烈,甚至出现卷渣现象。卷渣现象可通过调整搅拌器安装位置,或者调整浸入式水口深度改善。

超声波辅助液态法制备铝基复合材料的研究进展

简要介绍了超声波在液态法制备颗粒增强铝基复合材料中的作用,高能超声波除了可净化铝熔体及细化晶粒外,还可改善铝基体与增强体的润湿性、提高界面结合强度、促进增强体的分散性和控制反应生成的增强体颗粒尺寸。重点概述了超声波辅助原位反应法和外加法制备颗粒增强铝基复合材料的最新研究进展,总结了当前超声波辅助液态法制备铝基复合材料所遇到的问题,并展望今后的研究方向。

铝及铝合金熔铸新技术

文章介绍了近5~10年来铝及铝合金熔铸方面出现的一些新技术,指出了其基本工作原理和相应的优点,同时将一些正在研发和推广的对铝熔铸行业有较大影响的技术一并简单介绍,为读者在熔铸设备的选择及更新换代上提供参考。

SiC含量对铝基复合材料组织与力学性能的影响

采用半固态-液态搅拌铸造法制备了SiC颗粒增强铝基复合材料。研究了SiC颗粒含量(质量分数分别为0、5%、10%、15%和20%)对铝基复合材料组织及力学性能的影响。结果显示:添加少量SiC颗粒时,SiC颗粒在基体中分散均匀;当SiC质量分数达到15%时,SiC颗粒团聚较严重。随着SiC颗粒含量的增加,复合材料的硬度和抗拉强度先升高后降低。原因是SiC颗粒的位错强化作用,使得铝基复合材料的力学性能得到提升。随着SiC颗粒含量的增加,与界面结合良好的含Mg相数量减少,并且SiC颗粒团聚严重,铝基复合材料的力学性能降低。

一种降低铝锭铸造过程中铝液烧损的混合炉设备配置方法

本文分析了铝锭铸造过程铝液烧损的机理以及导致铝液烧损率高的主要原因,指出造成铝液烧损率高的主要原因是铝液转注以及搅拌方法不当而造成的,提出了一种降低铝液烧损的混合炉设备配置方法。

消除电磁搅拌连铸坯中“白亮带”的试验研究

针对电磁搅拌连铸坯中的“白亮带”问题进行试验研究和理论分析．结果表明：铸坯凝固过程中电磁搅拌引起的钢液运动特点是能否产生“白亮带”的关键．特殊的电磁搅拌方式有效地抑制“白亮带”的产生．

改善弹簧钢55SiCrA-1连铸坯碳偏析的工艺实践

Φ13 mm 55SiCrA-1钢(0.55%C)的生产流程为脱S铁水-80 t BOF-LF-RH-280 mm×325 mm坯连铸-轧制。所生产的Φ13 mm55SiCrA-1钢在冷拉过程中出现异常断裂,金相分析结果表明,盘条心部存在明显的黑点,且中心相邻区域出现负偏析现象。通过优化钢水过热度(15～25℃),二冷比水量(0.25 L/kg),结晶器电磁搅拌电流(300 A)和轻压下量(辊Ⅰ-1 mm,Ⅱ-2.5 mm,Ⅲ-3.5 mm,Ⅳ-3.5 mm和V-2 mm)使碳在铸坯横截面上分布趋于均匀,碳含量范围由原来0.49%～0.63%降至0.52%～0.60%,使冷拔断丝率由原7%降至0.5%。

电磁搅拌作用下水口深度对液面波动的影响

结晶器内液面波动会影响连铸坯的质量,施加电磁搅拌使钢液的液面呈旋转抛物面。电磁搅拌电流过大或拉速过高会造成保护渣卷渣现象,对铸坯质量造成不利的影响。以某钢厂?250 mm连铸圆坯结晶器电磁搅拌为研究对象,采用电磁-流体单相耦合的方式及流体体积函数VOF模型,建立描述结晶器电磁搅拌作用下液面波动的数学模型,研究电磁搅拌作用下浸入式水口深度对液面波动的影响。研究表明,通过增大水口深度,能够改善因电磁搅拌强度过大或拉速过大造成的卷渣现象,减小水口附近的液面波动。

双螺旋流变压铸AZ91D镁合金的研究

液态压铸是镁合金最主要的成形方式,但液态压铸件存在气孔等缺陷,限制了镁合金的进一步推广使用。介绍了采用双螺旋流变制浆技术,对镁合金AZ91D进行了流变压铸研究。首先,将镁合金AZ91D熔体浇入到双螺旋流变制浆机中,然后根据不同工艺参数制备流变镁合金浆料,待制浆结束后,将半固态浆料转移到压铸机内,制得半固态压铸件。采用Micro-Image Analysis&Process(MIAP)软件分析了双螺旋流变制浆工艺参数(搅拌温度、搅拌时间和转速)对镁合金AZ91D的初生相晶粒大小的影响,并研究了镁合金压铸成形性。结果表明:随着搅拌温度的降低,晶粒尺寸变化不是很大;随着搅拌时间延长,镁合金晶粒尺寸逐渐增大;随着搅拌速度的增加,镁合金平均晶粒尺寸减少。镁合金流变压铸件中的初生α相由搅拌中形成的球状晶及压铸过程中二次凝固形成的更为细小的球状晶组成。对比了普通压铸件与流变压铸件热处理后的力学性能,流变压铸件的力学性能得到大幅提高,其原因归结为铸态组织的细小和均匀化。

凝固末端螺旋电磁搅拌对大圆坯裂纹形成的影响

内部裂纹是特殊钢大圆坯常见缺陷之一。电磁搅拌是提高铸坯组织成分均匀性的常用技术手段,其中单绕组螺旋电磁搅拌器不仅结构简单、安装方便而且搅拌效果明显。为了探究凝固末端单绕组螺旋电磁搅拌(F-HEMS)对大圆坯内部钢液流动、凝固传热和裂纹形成的影响,采用试验和数值模拟方法进行研究,发现液相穴内钢液受电磁力作用,沿拉坯方向在电磁搅拌器高度范围内螺旋流动。F-HEMS使连铸坯内零塑性温度(TZD)至黏滞性温度(TLI)区间的温度梯度增大了31.56%~42.27%,使T_(ZD)-T_(LI)区间宽度减小了6.6 mm。受F-HEMS影响,糊状区内的液相分数降低。连铸坯内的温度、Von-Mises应力与弹性等效应变分布均呈层状分布。在应用F-HEMS后,连铸坯T_(ZD)-T_(LI)区间内的Von-Mises应力平均降低了0.11 MPa,弹性等效应变平均降低了0.02百分点。在数值模拟和试验的基础上,提出了一种开裂指数,以预测内部开裂风险。研究发现,应用F-HEMS时的开裂指数比未应用时的小0.158~0.280,证明F-HEMS有降低连铸坯裂纹形成概率的作用。然而,内部裂纹的形成受多种因素的影响,连铸过程中大圆坯的开裂预测仍需改进模拟方法并通过大量试验数据验证。F-HEMS影响连铸大圆坯内部的钢液流动和凝固传热,可降低内部裂纹的形成概率,本研究为工业生产提供了理论依据。