脉冲电流对ZA-27合金凝固组织的影响

研究了脉冲电流对ZA-27合金凝固组织的影响。结果表明，在金属液凝固过程中对其施加脉冲电流，能够使合金的凝固组织得到改善，晶粒得到细化，枝晶间距减小。其主要原因是脉冲电流产生的脉冲压力对晶核的形成和长大产生了影响。     

旋转磁场对牺牲阳极镁锰合金液态成形过程中α-Mn偏析的影响

针对牺牲阳极镁锰合金在液态成形过程中α-Mn极易产生偏析,造成牺牲阳极效率严重下降的问题,重点研究了不同强度的旋转磁场对牺牲阳极镁锰合金液态成形过程中α-Mn偏析的影响。实验结果表明:旋转磁场的搅拌作用不仅能明显改善镁锰合金中α-Mn的偏析,还能有效细化镁锰合金的晶粒。随激磁电压的增大,α-Mn偏析得到改善,且晶粒细化更明显。激磁电压为60V时,镁锰合金的硬度值最高,在人造海水中的耐蚀性最好。初步探讨了旋转磁场搅拌作用对牺牲阳极镁锰合金液态成形过程中α-Mn偏析改善机理。分析认为:旋转磁场强烈的搅拌作用使Mn在镁锰合金中分布更均匀,成形过程中晶核增多,冷却速度提高,快速凝固是α-Mn偏析改善及镁锰合金晶粒细化的根本原因。     

电磁搅拌对Cu-6%Ag合金凝固组织及硬度的影响

通过组织观察与硬度测试的方法研究了电磁搅拌对Cu-6%Ag合金凝固组织及硬度的影响。结果表明:施加电磁搅拌后,Cu-6%Ag合金的晶粒细化,初生铜枝晶变短、变粗,共晶组织细化,呈网状,铜枝晶内的银含量降低,铜枝晶的硬度由82HV升高至88HV。     

超声功率对半连续铸造7050铝合金晶粒细化的影响

在7050铝合金半连续铸造过程中引入超声场,研究了超声功率对铸锭凝固组织的影响规律,并探讨了超声细化晶粒的机理。结果表明:在半连续铸造过程中引入超声场后,7050铝合金的凝固组织晶粒明显细化,这主要是由于超声波在铝合金熔体中产生的空化效应和声流效应的影响,并且随着超声功率的提高,合金晶粒细化效果更好。     

外加能场消除钢凝固成形缺陷的研究进展

综述了外加能场(电磁场和超声场)消除钢凝固成形缺陷的研究进展。在钢液凝固过程中施加电磁场主要是借助于电磁力的搅拌作用,达到细化晶粒,减轻疏松、偏析和裂纹的目的;在钢液凝固过程中施加超声场主要是借助于超声波的空化效应和声流效应,实现细化晶粒,减少夹杂物,从而提高钢的力学性能;施加电磁-超声复合能场是消除大尺寸连铸钢坯凝固成形缺陷的新方法,并对其后续研究提出了几个需要考虑的问题。     

不同晶粒细化剂对5083铝合金铸锭晶粒细化对比研究

采用坩埚熔炼炉以及自主设计铸锭冷却系统模拟工业生产半连续铸造技术,通过不添加晶粒细化剂以及添加Al-Ti5-B1和Al-Ti3-C0.15两类晶粒细化剂制备3种5083铝合金铸锭,采用直读光谱分析、室温拉伸、金相研究在不同晶粒细化剂的条件下的力学性能、偏光显微组织、合金元素成分变化规律。研究结果表明：在铸造过程中添加Al-Ti-B或Al-Ti-C晶粒细化剂,通过细化剂中的Ti Al3和Ti B2颗粒能够有效的对铝合金显微组织起到细化作用,且越细小、越弥散,则可形成的非均匀形核核心越多,晶粒细化效果越显著,对比晶粒尺寸可知,Al-Ti5-B1晶粒细化剂效果最佳,Al-Ti3-C0.15晶粒细化剂其次;在合金凝固的过程中,由于不同元素在液相与固相的溶解度差异,从而导致5083合金铸锭中Mg、Mn、Cr、Fe、Si等元素成分差异,虽然添加晶粒细化剂能够促进熔体在凝固过程中的形核从而有一定作用抑制偏析,但晶粒细化剂对5083铝合金的偏析改善不明显;添加晶粒细化剂的铸锭晶粒细小,晶界多,位错集群中位错个数小,应力集中小,从而导致添加晶粒细化剂的5083铸锭室温力学性能优于未添加晶粒细化剂。     

Al—37%Si合金磷变质及电磁搅拌显微组织的研究

对Ａｌ－３７％Ｓｉ合金进行了磷变质及电磁搅拌处理。结果表明，磷变质可使合金的显微组织取得了部分细化效果，初晶硅从粗大板条状为主过渡到较小块状为主，但不能完全消除粗大板条状的初晶硅。电磁搅拌可使合金的显微组织得到明显改善，初晶硅基本上呈块状或细小板条状，且棱角比较圆滑，并在显微组织中有近球形的α相存在。     

多次循环淬火工艺参数对10Ni5CrMoV钢晶粒细化的影响

对10Ni5CrMoV钢在930～1030℃进行不同保温时间、不同次数的循环淬火,采用光学显微镜观察显微组织变化,并探讨了加热温度、保温时间、循环次数对晶粒尺寸的影响,对热处理前后该钢的力学性能和断口形貌进行了分析。结果表明:不同温度下随着保温时间的延长,晶粒尺寸逐渐增大,100 s时最佳;循环次数小于3时晶粒粗大且不均匀,大于3时细化效果增加不明显;随加热温度升高,晶粒尺寸先降后增,950℃最细小;细化晶粒的最佳工艺为加热温度950℃、保温100 s、3次循环淬火,可使晶粒尺寸由253μm细化至63μm,淬回火后钢的强度及塑韧性均有明显提高。     

电磁搅拌对LD10CS铝合金焊接接头晶粒细化效果及其强度改善的研究

通过分析外加磁场Ｈｅ－ＴＩＧ焊接ＬＤ１０ＣＳ铝合金的焊缝组织,发现外加磁场的磁感应强度Ｂ和磁场交变频率ｆ对接头晶粒细化效果的影响最大。磁感应强度Ｂ与磁场交变频率ｆ不能单独选择,必须恰当匹配,而且还必须与焊接规范参数相适应,才能保证获得最佳的晶粒细化。同时,本文在该试验条件下研究了该电磁搅拌方法对铝合金焊接接头强度的影响,以指导磁控电弧焊接生产。     

熔体混合与半固态电磁搅拌复合处理对初生Si相细化的研究

本文分别采用半固态电磁搅拌法和熔体混合结合电磁搅拌技术来制备Al-20%Si合金,研究表明单纯采用电磁搅拌技术制备Al-20%Si时,会产生偏析层,其初生Si平均尺寸在60μm以上;而采用熔体混合+电磁搅拌复合处理可使Al-20%Si合金中的初生Si尺寸降至16μm以下,可消除在单纯电磁搅拌合金边缘出现的粗大的初生Si的偏析层,并且熔体混合处理处理还可以强化过共晶Al-20%Si合金的电磁搅拌效果,可获得良好细化效果.     

COMPUTER SIMULATION OF CONTINUOUS ELECTROMAGNETIC STIRRING FOR MAKING RHEOLOGIC SEMI-SOLID SLURRY OF ZL112Y ALUMINUM ALLOY

To realize the technology of fabricating the rheologic semi-solid slurry of ZL112Y aluminum alloy via continues electromagnetic stirring process, ANSYS software was used to simulate electromagnetic force field and fluid velocity field in the alloy melt in a crucible tube in three coils. In the first section of the paper, eletromagnetic force field and fluid velocity field caused by single coil were simulated. The result of this simulation gives an average velocity of 3.2 cm/s and it is called critical velocity because a fluid velocity over it will cause a fine and spherical structure of solid primary a in a semi-solid melt. And, from this result, a reasonable temperature of semi-solid of the alloy and an electrical current intensity were established. The electrical current intensity of the result of this simulation corresponded to the current intensity used in a practice experiment, in which the primary α was obviously refined and sphericized. Based on this simulation of single coil electromagnetic stirring, in the second section of the paper, eletromagnetic force field and fluid velocity field caused by three coils were simulated. The result of the simulation shows that, 1） there is a semi-solid zone of 32 mm from bottom of the crucible tube to the upper; 2） the electrical current intensities of three coils of 400 A, 600 A, and 400 A, which were set to top range, middle range and bottom range of the tube, respectively, were the optimum parameters of electromagnetic current intensity under the condition of this investigation; and 3） under effect of these electromagnetic current intensity, the fluid velocities of the melt in the tube were 6.3 cm/s in top range, 3.75 cm/s in middle range, and 3.9 cm/s in bottom range of it, respectively.     

镍对高铝锌合金组织和性能的影响

着重研究了金属元素镍对高铝锌合金ZA-27的结晶组织、枝晶成分偏析以及常温和高温机械性能和耐蚀性能的影响。试验结果表明,金属元素镍可以改善ZA-27合金在常温与高温下的机械性能,并且对其耐磨性能和耐热性能均有利。     

马氏体组织Ti-6Al-4V钛合金多向等温锻造组织演变及力学性能强化研究

将铸态Ti-6Al-4V钛合金经过β相区热处理水淬之后获得马氏体组织,经过两步多向等温锻造之后获得了平均晶粒尺寸为1.5 μm的均匀等轴细晶组织,其室温拉伸屈服强度为906 MPa,抗拉强度为954 MPa,伸长率为16.7%,相比铸态Ti-6Al-4V钛合金,其室温力学性能得到了极大提升。研究表明,获得马氏体组织对钛合金晶粒细化有着巨大促进作用。第一步等温锻造之后的钛合金坯料组织并不均匀,存在变形区和“变形死区”,在变形区域内,心部位置应变量最大,组织细化最为明显,从心部到两端应变量逐渐减小,片层组织变形量相应减小;经过90°换向后的第二步等温锻造之后,钛合金坯料组织内的片层组织基本全部细化,形成了均匀的等轴晶组织,从心部到两端,随着应变量的减小,晶粒取向变化相应减小。     

The influences of shear deformation on the evolutions of the extrusion shear for magnesium alloy

A new type of magnesium alloy extrusion-shear (short for ES) composite extrusion technology which combines the characteristics of direct extrusion and two pass equal channel extrusion has been put forward. The experiments of ES process and direct extrusion have been performed, and direct extrusion and ES dies suitable for industrial horizontal extruder have been designed and manufactured. Three-dimensional thermomechanical finite element models and conditions of the ES process and direct extrusion have been established. Extrusion forces and accumulated strains and stresses and temperatures evolution of the ES process have been obtained. The loads of the ES process increase obviously compared with those of direct extrusion. Maximum temperatures during the ES process are higher than those of direct extrusion. The computer simulation analyses of stress state for the billets reveal that part of the billet is exerted in four directions of compressive stress. The ES process could cause cumulative strains and shear stress in magnesium alloy billets than direct extrusion. Therefore, more grain refinements could be achieved. Based on the microstructure observations of center positions for the ES process and direct extrusion rods, grains have been effectively refined with extrusion temperature. It is found that there are many similarities between finite element simulation results and experimental results.     

Effects of electromagnetic stirring and rare earth compounds on the microstructure and mechanical properties of hypereutectic Al–Si alloys

In this paper, the effects of rare earth addition and electromagnetic stirring on the microstructure and the mechanical properties of hypereutectic Al–Si alloys have been reported. Hypereutectic Al–Si alloy was prepared using liquid metallurgy route and modified with the addition of cerium oxide. To control the structure, slurry of hypereutectic Al–Si alloy was subjected to electromagnetic stirring before pouring into the mould. It was observed that the addition of cerium oxide (0.2 wt.%) refined the primary silicon particles and modified the eutectic silicon particles. Further, the electromagnetic stirring of the hypereutectic Al–Si alloy reduced the average size of primary silicon particles, from 152?±?9 to 120?±?6 μm, and the length of β-intermetallic compounds decreased from 314?±?12 to 234?±?10 μm. Similarly, the application of electromagnetic stirring on cerium oxide-modified hypereutectic Al–Si alloy also reduced the average size of primary silicon particles from 98?±?5 to 76?±?4 μm and the average length of β-intermetallic compounds from 225?±?7 to 203?±?5 μm. Mechanical properties namely tensile strength, ductility and hardness of the alloys were improved with electromagnetic stirring and addition of cerium oxide appreciably.     

Dry sliding wear of short glass fibre reinforced zinc–aluminium composites

The present investigation aims to evaluate the wear rate of ZA-27 alloy composites reinforced with short glass fibres from 1 to 5% in steps of 2 wt%. The compocasting method was used to fabricate the composites. A pin-on-disc wear testing machine was used to evaluate the wear rate. The results indicated that the wear rate of the composites was less than that of the matrix alloy, but increased with the increase in load and the sliding distance. It was found that above a critical applied load, there exists a transition from mild to severe wear both in the unreinforced alloy and in the composites, but the transition loads for the composites are much higher than that of the unreinforced alloy, and increases with the increase in weight% of glass fibres. The observations have been explained using scanning electron micrography (SEM) analysis of the worn surfaces and the subsurface of the composites.     

Wear Behavior of Composites Based on ZA-27 Alloy Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles Under Dry Sliding Condition

In present study, the effect of Al₂O₃ particle reinforcement on the sliding behavior of ZA-27 alloy composites was investigated. The composites with 3, 5, and 10 wt% of Al₂O₃ particles were produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer under unlubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of samples were examined by the scanning electron microscopy (SEM). The test results revealed that those composite specimens exhibited significantly lower wear rate than the ZA-27 matrix alloy specimens in all combinations of applied loads and sliding speeds. The difference in the wear resistance of composite with respect to the matrix alloy, increased with the increase of the applied load/sliding speed and Al₂O₃ particle content. The highest degree of improvement of the ZA-27 alloy tribological behavior corresponded with change of the Al₂O₃ particles content from 3 to 5 wt%. At low sliding speed, moderate lower wear rate of the composites over that of the matrix alloy was noticed. This has been attributed to micro cracking tendency of the composites. Significantly reduced wear rate, experienced by the composite over that of the matrix alloy at the higher sliding speeds and loads, could be explained due to enhanced compatibility of matrix alloy with dispersoid phase and greater thermal stability of the composite in view of the presence of the dispersoid. Level of wear rate of tested ZA-27/Al₂O₃ samples pointed to the process of mild wear, which was primarily controlled by the formation and destruction of mechanical mixed layers (MMLs).     

Zn含量对Mg-9Al镁合金显微组织的影响

通过光学显微镜、扫描电镜和万能力学试验机等设备研究了Zn含量对镁合金铸态和半固态显微组织变化的影响。研究表明,随着Zn含量的增加,合金的铸态显微组织得到了细化,合金的半固态组织的晶粒明显细小、圆整。当等温热处理温度为570℃、保温时间为30min时,半固态显微组织最好,其中,Mg-9Al-1Zn合金的颗粒尺寸为74μm,Mg-9Al-3Zn合金的颗粒尺寸为68μm,Mg-9Al-5Zn合金的颗粒尺寸为57μm。     

A study on semisolid processing of A356 aluminum alloy through vacuum-assisted electromagnetic stirring

In this study, a vacuum-assisted electromagnetic stirring system was designed and manufactured in order to minimize the defects such as porosities in the semisolid processing A356 aluminum alloy by electromagnetic stirring (EMS). A sleeve cooling system was manufactured and two different cooling media (air and water) were tested for the stirred and unstirred slurries. For the stirred slurry, the obtained cooling rates were lower than the values for the unstirred slurry in both cooling media. Also the effects of the different cooling types and the thickness of the slurry cup on the microstructural evolution were thoroughly studied. The maximum cooling rate with the least evidence of the liquid segregation for the stirred slurry was achieved in water-cooling condition when the slurry cup of 2 mm thickness was used. At the pouring temperature of 620^o, the optimum EMS stirring current and time were obtained 30 A and 60 s, respectively. The vacuum level with the least presence of the porosity was determined at 50 kPa, while further increase in the vacuum level (decrease in the applied pressure) resulted in increase in the presence of the porosity. The last trend could be attributed to the possible effect of the stirring during the EMS process on the entrainment of bifilms into the semisolid slurry, which is discussed in details.