喷射成形过共晶Al-Si合金的组织特征和磨损行为

采用喷射成形技术制备了过共晶Al-Si耐磨合会,分析了合金的显微组织结构,利用M200磨损试验机对喷射成形和铸造Al-Si合金的耐磨性和磨损失效形式进行了分析比较。结果表明：喷射成形能够显著改变过共晶Al-Si合金中初晶Si相的形态和尺寸,细化合金的基体组织;与普通铸造合金相比,具有更好的耐磨性能。     

二次加热过程中半固态AZ31镁合金的显微组织演变

利用波浪形倾斜板振动技术制备AZ31镁合金半固态坯料,获得较为理想的球形或近球形晶粒组织。结果表明:随二次加热温度的升高和保温时间的延长,半固态组织中的液相体积分数增大,固相逐渐长大并球化;AZ31镁合金580℃和610℃时二次加热组织均不适合半固态触变成形;适合触变成形的二次加热最优工艺为590℃保温40～60 min、或者600℃保温30 min;此条件下获得的平均晶粒直径为58～61μm,固相率为87%(体积分数)左右。晶格扩散机制对二次加热原子扩散起主导作用,是造成合金固相颗粒尺寸变化的根本原因;固液界面张力是造成颗粒形状球形或近球形变化的重要原因。     

喷射成形共晶铝硅合金的成形性研究

本文即针对喷射成形共晶铝硅合金成形性进行研究 ,采用Gleeble15 0 0实验机进行压缩比实验 ,并同时量测流动应力。本研究以涡卷式压缩机用之涡卷转子为载具 ,进行共晶铝硅合金锻件的开发分析。试锻结果确认喷射成形共晶铝硅合金具有近似于 60 61及 40 3 2的成形性 ,在相同锻造条件下 ,涡卷端面平面度与 60 61及 40 3 2并无显著差异     

Microstructure evolution during reheating of extruded Mg-Gd-Y-Zr alloy into semisolid state

The microstructure evolution of an extruded Mg-8.57Gd-3.72Y-0.54Zr (mass fraction, %, GW94) alloy during reheating into the semisolid state was investigated using optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Typical semisolid microstructure with globular solid particles distributed in the liquid matrix is obtained over 600 °C. The solid content of (Gd+Y) in the primary a-Mg particles decreases with increasing the semisolid temperature. With the prolongation of isothermal holding time, the liquid fraction does not change significantly, while the grains grow up and spheroidize. Three methods used to determine the liquid fraction as a function of temperature, namely quantitative metallography on quenched microstructures, cooling curve thermal analysis, and thermodynamic calculations were further compared.     

Mechanical properties of hypereutectic Al-Si alloy by semisolid processing

1　ＩＮＴＲＯＤＵＣＴＩＯＮＨｙｐｅｒｅｕｔｅｃｔｉｃＡｌ Ｓｉａｌｌｏｙｓｏｗｎｅｘｃｅｌｌｅｎｔｗｅａｒｒｅｓｉｓｔａｎｃｅ .Ｈｏｗｅｖｅｒ ,ｔｈｅｓｉｚｅａｎｄｍｉｃｒｏｓｔｒｕｃｔｕｒｅｏｆｐｒｉｍａｒｙｓｉｌｉｃｏｎｈａｖｅ ｇｒｅａｔｅｆｆｅｃｔｏｎｉｔｓ ｐｒｏｐｅｒｔｉｅｓ ,ｔｈｅｎｔｈｅｐｒｅｓｅｎｔｓｔｕｄｉｅｓｍａｉｎｌｙｆｏｃｕｓｏｎｔｈｅｉｍｐｒｏｖｅ ｍｅｎｔｏｆｔｈｅｐｒｉｍａｒｙｓｉｌｉｃｏｎｓｉｚｅａｎｄｍｉｃｒｏｓｔｒｕｃｔｕｒｅｂｙｍｅａｎｓｏｆｍｏｄｉｆｉｃａ…     

Effect of hot extrusion process on microstructure and mechanical properties of hypereutectic Al-Si alloys

The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.     

Microstructure and mechanical properties of hypereutectic Al-Si alloy modified with Cu-P

The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The results indicate that the Cu-P master alloy possesses not only obvious modification effect,but also longevity effect with more than 8 h on the hypereutectic Al-Si alloy.It is shown from thermal calculation,scanning electron microscope（SEM）,and energy dispersive analysis of X-rays（EDAX） that the modification mechanism of Cu-P on primary silicon in the castings is heterogeneous nucleation around AlP particles.The Cu-P master alloy has no or little modifying effect on eutectic silicon,even though it has obvious modification on primary silicon in the castings.This may be because of the fast transformation of eutectic silicon at a very narrow temperature,which will notably weaken the role of AlP particles as heterogeneous nuclei for eutectic silicon.     

Effects of vibration and grain refiner on microstructure of semisolid slurry of hypoeutectic Al-Si alloy

The effects of vibration and grain refiner on the microstructure of semisolid slurry of hypoeutectic Al-Si alloy were studied. The impact of vibration on the convection of liquid was conducted by using a system of water-particle tracer. The 356 melt at temperature of 630-660 ℃ with or without grain refiner Al-5%Ti-1%B was poured into a metal cup as the vibrating vessel, then it was cooled to 590-610 ℃ in the semisolid zone and kept for some time, subsequently vibration with different frequencies was applied. The results show that the primary a（Al） particles become finer and rounder with the increase of vibration frequency. The slurry with primary a（Al） equivalent particle diameter（EPD） of about 90μm and average shape coefficient（ASC） of about 0.5 can be prepared under vibration of 20 Hz. With the combined action of vibration and grain refiner Al-5Ti-B, even smaller and rounder spheroids with EPD of about 85μm and ASC of about 0.6 are obtained.     

Simulation for microstructure evolution of Al-Si alloys in solidification process

The numerical simulation for microstructure evolution of Al-Si alloy in solidification process is carried out with phase field model. The phase field model, solution algorithm and the program of dendrite growth are introduced. The definition of initial condition, boundary condition and the stability condition of differential format are all included. The simulation results show that the evolution of dendrite morphology is as follows： the initial circle nucleus transforms to the rectangle one firstly, then its corners develop to the four trunks and from which the secondary side branches are generated and even the third side branches are produced from secondary ones. The dendrite tip radius decreases quickly at the initial stage and changes slowly at the late stage, which is mainly due to the fact that more and more side branches appear and grow up. The comparisons of dendrite morphology between simulated results and investigations by others are also presented. It is proved that the dendrite morphologies are similar in trunks and arms growth, so the developed phase field program is accurate.     

过共晶铝硅自生梯度复合材料的组织与性能

用电磁分离工艺成功制备了初生Si相体积分数、材料显微硬度和耐磨性沿径向呈梯度分布的棒状复合材料 ,讨论了梯度层的形成过程。微观组织观察和力学性能测试结果表明 :在近外壁区域形成了体积分数高达16 %的细小初生Si相偏聚区 ,此区硬度高 ,耐磨性好 ,中心区为细小和均匀的共晶组织 ,两部分之间为颗粒体积分数渐变的过渡区 ,可使耐磨层与基体的结合强度得到保证     

喷射成形Mg-9Al-xZn合金的微观组织演变

利用喷射成形技术制备AZ91、AZ92和AZ93镁合金沉积柱坯,并对其微观组织演变进行观察.结果表明:铸态普通凝固AZ91合金的晶粒粗大,脆性β-Mg17Al12相连续分布成网状结构;而喷射成形AZ91、AZ92和AZ93合金的组织均匀,晶粒被充分细化,β-Mg17Al12相的网状结构被打破;喷射沉积快速凝固条件下高的冷却速率促进了过饱和α-Mg固溶体组织的形成,使得偏析相减少,形态改善;Zn含量的增加降低了Al在Mg中的溶解极限,促进了β-Mg17Al12相在晶界的析出及α-Mg+β-Mg17Al12离异共晶组织的形成;Zn元素的偏析倾向为激活成分过冷区内的形核质点提供了驱动力,从而阻碍了晶粒长大.     

Influence of La on microstructures of hypereutectic Al-Si alloys

1　INTRODUCTIONThemicrostructureofhypereutecticAl Sialloys ,preparedbyconventionalcastingroutines ,usuallyconsistsofcoarseSicrystals[112 ] ,leadingtothepoorextrudability ,machinability ,strengthandductili ty[1315] .Therefore ,structuralmodificationmustbedonethroughtwo generalways :1)alloyingaddi tions ,and /or ;2 )syntheticalternatives .Accordingtothedimensionalconditionofaneffectivemodifier ,theradiusratiooftheagenttoSishouldbeabout1.6 5 [16 ] ,La ,withtheratioof 1.5 9,ispossiblycon sid…     

喷射沉积高硅铝合金显微组织及形成机理

研究了喷射沉积Ａｌ－２０％Ｓｉ及Ａｌ－３０％Ｓｉ合金坯料的显微组织及形成机理。结果表明,两种合金的喷射沉积态组织为细小的团块状Ｓｉ均匀地分布于基体α上,没有共晶组织出现。形成该组织特征的机理是由于在沉积阶段凝固过程中合金发生了离异共晶,在雾化阶段大的冷却速度下形成的大量Ｓｉ相核心以及在沉积阶段相对较低的冷却速度为这一过程提供了动力学条件。通过自行设计的沉积阶段凝固的模拟实验,对这一机理进行了验证;     

On the modification of hypereutectic Al-Si alloys using rare earth Er

Hypereutectic Al-17.5Si (wt pct) and Al-25Si (wt pct) alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.     

过共晶Al-Si合金熔体中初生硅生长特性

利用等温液淬的方法,研究了Al-18%Si过共晶合金熔体中初生硅的生长行为及机制.结果表明:重熔过程中熔体中未溶解的硅相粒子,在凝固过程中可成为初生硅生长核心,并且未熔颗粒与初生硅形状之间存在明显对应关系; 初生硅的生长机制不是惟一的,既可以以孪晶凹角(TPRE)机制生长,还可以以层状机制生长,初生硅最终形状还要取决于溶质传输等动力学环境; 随着熔体过热温度的升高,凝固组织中初生硅形状由多边形向星形及树枝状转变.     

气雾化过共晶Al-Si合金粉末的形貌、组织和结构

采用扫描电镜、差热分析仪和X射线衍射仪分析粒度对气雾化过共晶Al-Si合金粉末形貌、组织和结构的影响,并计算粉末的过冷度和冷却速度。结果表明：粉末形貌规则性随粒度减小而得到改善,但Si相分布均匀性降低;同时,初晶Si相尺寸逐渐减小,形貌由不规则状转为块状;共晶Si相由不均匀针状转为网络状。随粒度减小,Al基体衍射峰发生宽化和偏移,同时热效应前移。过冷度和冷却速度随粒度减小而增大,这是导致粉末间组织和结构差异的根本原因。     

混合方式对受控扩散凝固过共晶Al-Si合金初生硅相的影响

采用受控扩散凝固技术(CDS)制备Al-15％Si(质量分数)合金,研究混合方式对受控扩散凝固Al- 15％Si合金初生硅相尺寸、形貌和分布的影响.结果表明:受控扩散凝固可以明显细化初生硅相,改善初生硅相形貌和在组织中的分布.其中,液-液混合细化效果比固-液混合细化效果好,特别是通过液态纯铝与液态Al-25％Si合金的液-液混合受控扩散凝固制备得到的凝固组织,其初生硅相平均尺寸仅为14μm,且在组织中分布均匀.     

过共晶铝-硅合金处理技术的研究进展

综述了为改善过共晶铝-硅合金的性能,目前所采用的控制合金中初晶硅尺寸、形态和分布的各种处理方法及其机制,它们包括细化变质、合金熔体过热处理、半固态搅拌、快速凝固、电磁场作用、电脉冲孕育处理等方法。从合金中初晶硅尺寸、形态和分布等方面比较了各种处理方法的优缺点。     

喷射成形AZ91镁合金的显微组织和力学性能

采用喷射成形和沉积坯热轧的方法成功制备了AZ91镁合金,测试了合金的力学性能,分析了合金的强化机理.结果表明:喷射成形的镁合金坯晶粒细小,组织均匀,第二相化合物Mg17Al12数量较少,表现出良好的塑性变形能力,道次变形量在20%左右,两次退火间的总变形量可以达到50%.经80%热轧变形后,合金完全致密化.变形使合金晶粒进一步细化,力学性能显著提高.轧制后合金基体中仍保持很高的固溶度,经T5处理后,合金的力学性能进一步提高.